Red Hat Enterprise Linux 6

Edition 1

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###### Abstract
This document describes the different features and utilities that make Red Hat Enterprise Linux 6 an ideal enterprise platform for application development. It focuses on Eclipse as an end-to-end integrated development environment (IDE), but also includes command-line tools and other utilities outside Eclipse.

Preface
1. Document Conventions
1.1. Typographic Conventions
1.2. Pull-quote Conventions
1.3. Notes and Warnings
2. Getting Help and Giving Feedback
2.1. Do You Need Help?
2.2. We Need Feedback!
1. Introduction to Eclipse
1.1. Understanding Eclipse Projects
1.2. Help In Eclipse
1.3. Development Toolkits
2. The Eclipse Integrated Development Environment (IDE)
2.1. User Interface
2.2. Useful Hints
2.2.2. libhover Plug-in
3. Collaborating
3.1. Concurrent Versions System (CVS)
3.1.1. CVS Overview
3.1.2. Typical scenario
3.1.3. CVS Documentation
3.2. Apache Subversion (SVN)
3.2.1. Installation
3.2.2. SVN repository
3.2.3. Importing Data
3.2.4. Working Copies
3.2.5. Committing changes
3.2.6. SVN Documentation
3.3. Git
3.3.1. Installation
3.3.2. Initial Setup
3.3.3. Git repository
3.3.4. Untracked files
3.3.5. Unmodified files
3.3.6. Modified Status
3.3.7. Staged files
3.3.8. Remote repositories
3.3.9. Commit logs
3.3.10. Fixing problems
3.3.11. Git documentation
4. Libraries and Runtime Support
4.1. Version Information
4.2. Compatibility
4.2.1. API Compatibility
4.2.2. ABI Compatibility
4.2.3. Policy
4.2.5. Core Libraries
4.2.6. Non-Core Libraries
4.3. Library and Runtime Details
4.3.1. The GNU C Library
4.3.2. The GNU C++ Standard Library
4.3.3. Boost
4.3.4. Qt
4.3.5. KDE Development Framework
4.3.6. NSS Shared Databases
4.3.7. Python
4.3.8. Java
4.3.9. Ruby
4.3.10. Perl
5. Compiling and Building
5.1. GNU Compiler Collection (GCC)
5.1.1. GCC Status and Features
5.1.2. Language Compatibility
5.1.3. Object Compatibility and Interoperability
5.1.4. Backwards Compatibility Packages
5.1.5. Previewing RHEL6 compiler features on RHEL5
5.1.6. Running GCC
5.1.7. GCC Documentation
5.2. Distributed Compiling
5.3. Autotools
5.3.1. Autotools Plug-in for Eclipse
5.3.2. Configuration Script
5.3.3. Autotools Documentation
5.4. Eclipse Built-in Specfile Editor
6. Debugging
6.1. Installing Debuginfo Packages
6.2. GDB
6.2.1. Simple GDB
6.2.2. Running GDB
6.2.3. Conditional Breakpoints
6.2.4. Forked Execution
6.2.6. Alternative User Interfaces for GDB
6.2.7. GDB Documentation
6.3. Variable Tracking at Assignments
6.4. Python Pretty-Printers
7. Profiling
7.1. Profiling In Eclipse
7.2. Valgrind
7.2.1. Valgrind Tools
7.2.2. Using Valgrind
7.2.3. Valgrind Plug-in for Eclipse
7.2.4. Valgrind Documentation
7.3. OProfile
7.3.1. OProfile Tools
7.3.2. Using OProfile
7.3.3. OProfile Plug-in For Eclipse
7.3.4. OProfile Documentation
7.4. SystemTap
7.4.1. SystemTap Compile Server
7.4.2. SystemTap Support for Unprivileged Users
7.4.3. SSL and Certificate Management
7.4.4. SystemTap Documentation
7.5. Performance Counters for Linux (PCL) Tools and perf
7.5.1. Perf Tool Commands
7.5.2. Using Perf
7.6. ftrace
7.6.1. Using ftrace
7.6.2. ftrace Documentation
8. Documentation Tools
8.1. Publican
8.1.1. Commands
8.1.2. Create a New Document
8.1.3. Files
8.1.4. Building a Document
8.1.5. Packaging a Publication
8.1.6. Brands
8.1.7. Building a Website
8.1.8. Documentation
8.2. Doxygen
8.2.1. Doxygen Supported Output and Languages
8.2.2. Getting Started
8.2.3. Running Doxygen
8.2.4. Documenting the Sources
8.2.5. Resources
A. Revision History
Index

# Preface

This book describes the some of the more commonly-used programming resources in Red Hat Enterprise Linux 6. Each phase of the application development process is described as a separate chapter, enumerating tools that accomplish different tasks for that particular phase.
Note that this is not a comprehensive listing of all available development tools in Red Hat Enterprise Linux 6. In addition, each section herein does not contain detailed documentation of each tool. Rather, this book provides a brief overview of each tool, with a short description of updates to the tool in Red Hat Enterprise Linux 6 along with (more importantly) references to more detailed information.
In addition, this book focuses on Eclipse as an end-to-end integrated development platform. This was done to highlight the Red Hat Enterprise Linux 6 version of Eclipse and several Eclipse plug-ins.

## 1. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to specific pieces of information.
In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts set. The Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not, alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later includes the Liberation Fonts set by default.

### 1.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These conventions, and the circumstances they apply to, are as follows.
Mono-spaced Bold
Used to highlight system input, including shell commands, file names and paths. Also used to highlight keycaps and key combinations. For example:
To see the contents of the file my_next_bestselling_novel in your current working directory, enter the cat my_next_bestselling_novel command at the shell prompt and press Enter to execute the command.
The above includes a file name, a shell command and a keycap, all presented in mono-spaced bold and all distinguishable thanks to context.
Key combinations can be distinguished from keycaps by the hyphen connecting each part of a key combination. For example:
Press Enter to execute the command.
Press Ctrl+Alt+F2 to switch to the first virtual terminal. Press Ctrl+Alt+F1 to return to your X-Windows session.
The first paragraph highlights the particular keycap to press. The second highlights two key combinations (each a set of three keycaps with each set pressed simultaneously).
If source code is discussed, class names, methods, functions, variable names and returned values mentioned within a paragraph will be presented as above, in mono-spaced bold. For example:
File-related classes include filesystem for file systems, file for files, and dir for directories. Each class has its own associated set of permissions.
Proportional Bold
This denotes words or phrases encountered on a system, including application names; dialog box text; labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:
Choose SystemPreferencesMouse from the main menu bar to launch Mouse Preferences. In the Buttons tab, click the Left-handed mouse check box and click to switch the primary mouse button from the left to the right (making the mouse suitable for use in the left hand).
To insert a special character into a gedit file, choose ApplicationsAccessoriesCharacter Map from the main menu bar. Next, choose SearchFind… from the Character Map menu bar, type the name of the character in the Search field and click . The character you sought will be highlighted in the Character Table. Double-click this highlighted character to place it in the Text to copy field and then click the button. Now switch back to your document and choose EditPaste from the gedit menu bar.
The above text includes application names; system-wide menu names and items; application-specific menu names; and buttons and text found within a GUI interface, all presented in proportional bold and all distinguishable by context.
Mono-spaced Bold Italic or Proportional Bold Italic
Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or variable text. Italics denotes text you do not input literally or displayed text that changes depending on circumstance. For example:
To connect to a remote machine using ssh, type ssh username@domain.name at a shell prompt. If the remote machine is example.com and your username on that machine is john, type ssh john@example.com.
The mount -o remount file-system command remounts the named file system. For example, to remount the /home file system, the command is mount -o remount /home.
To see the version of a currently installed package, use the rpm -q package command. It will return a result as follows: package-version-release.
Note the words in bold italics above — username, domain.name, file-system, package, version and release. Each word is a placeholder, either for text you enter when issuing a command or for text displayed by the system.
Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example:
Publican is a DocBook publishing system.

### 1.2. Pull-quote Conventions

Terminal output and source code listings are set off visually from the surrounding text.
Output sent to a terminal is set in mono-spaced roman and presented thus:
books        Desktop   documentation  drafts  mss    photos   stuff  svn
books_tests  Desktop1  downloads      images  notes  scripts  svgs
Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows:
package org.jboss.book.jca.ex1;

import javax.naming.InitialContext;

public class ExClient
{
public static void main(String args[])
throws Exception
{
InitialContext iniCtx = new InitialContext();
Object         ref    = iniCtx.lookup("EchoBean");
EchoHome       home   = (EchoHome) ref;
Echo           echo   = home.create();

System.out.println("Created Echo");

System.out.println("Echo.echo('Hello') = " + echo.echo("Hello"));
}
}

### 1.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

## Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note should have no negative consequences, but you might miss out on a trick that makes your life easier.

## Important

Important boxes detail things that are easily missed: configuration changes that only apply to the current session, or services that need restarting before an update will apply. Ignoring a box labeled 'Important' will not cause data loss but may cause irritation and frustration.

## Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

## 2. Getting Help and Giving Feedback

### 2.1. Do You Need Help?

If you experience difficulty with a procedure described in this documentation, visit the Red Hat Customer Portal at http://access.redhat.com. Through the customer portal, you can:
• search or browse through a knowledgebase of technical support articles about Red Hat products.
• submit a support case to Red Hat Global Support Services (GSS).
• access other product documentation.
Red Hat also hosts a large number of electronic mailing lists for discussion of Red Hat software and technology. You can find a list of publicly available mailing lists at https://www.redhat.com/mailman/listinfo. Click on the name of any mailing list to subscribe to that list or to access the list archives.

### 2.2. We Need Feedback!

If you find a typographical error in this manual, or if you have thought of a way to make this manual better, we would love to hear from you! Please submit a report in Bugzilla: http://bugzilla.redhat.com/ against the product Red_Hat_Enterprise_Linux.
When submitting a bug report, be sure to mention the manual's identifier: doc-Developer_Guide
If you have a suggestion for improving the documentation, try to be as specific as possible when describing it. If you have found an error, please include the section number and some of the surrounding text so we can find it easily.

## Chapter 1. Introduction to Eclipse

Eclipse is a powerful development environment that provides tools for each phase of the development process. It is integrated into a single, fully configurable user interface for ease of use, featuring a pluggable architecture which allows for extension in a variety of ways.
Eclipse integrates a variety of disparate tools into a unified environment to create a rich development experience. The Valgrind plug-in, for example, allows programmers to perform memory profiling (normally done through the command line) through the Eclipse user interface. This functionality is not exclusive only to Eclipse.
Being a graphical application, Eclipse is a welcome alternative to developers who find the command line interface intimidating or difficult. In addition, Eclipse's built-in Help system provides extensive documentation for each integrated feature and tool. This greatly decreases the initial time investment required for new developers to become fluent in its use.
The traditional (i.e. mostly command-line based) Linux tools suite (gcc, gdb, etc) and Eclipse offer two distinct approaches to programming. Most traditional Linux tools are far more flexible, subtle, and (in aggregate) more powerful than their Eclipse-based counterparts. These traditional Linux tools, on the other hand, are more difficult to master, and offer more capabilities than are required by most programmers or projects. Eclipse, by contrast, sacrifices some of these benefits in favor of an integrated environment, which in turn is suitable for users who prefer their tools accessible in a single, graphical interface.

## 1.1. Understanding Eclipse Projects

Eclipse stores all project and user files in a designated workspace. You can have multiple workspaces and can switch between each one on the fly. However, Eclipse will only be able to load projects from the current active workspace. To switch between active workspaces, navigate to File > Switch Workspace > /path/to/workspace. You can also add a new workspace through the Workspace Launcher wizard; to open this wizard, navigate to File > Switch Workspace > Other.

For information about configuring workspaces, refer to Reference > Preferences > Workspace in the Workbench User Guide (Help Contents).
A project can be imported directly into Eclipse if it contains the necessary Eclipse metafiles. Eclipse uses these files to determine what kind of perspectives, tools, and other user interface configurations to implement.
As such, when attempting to import a project that has never been used on Eclipse, it may be necessary to do so through the New Project wizard instead of the Import wizard. Doing so will create the necessary Eclipse metafiles for the project, which you can also include when you commit the project.

The Import wizard is suitable mostly for projects that were created or previously edited in Eclipse, i.e. projects that contain the necessary Eclipse metafiles.

## 1.2. Help In Eclipse

Eclipse features a comprehensive internal help library that covers nearly every facet of the Integrated Development Environment (IDE). Every Eclipse documentation plug-in installs its content to this library, where it is indexed accordingly. To access this library, use the Help menu.

To open the main Help menu, navigate to Help > Help Contents. The Help menu displays all the available content provided by installed documentation plug-ins in the Contents field.

The tabs at the bottom of the Contents field provides different options for accessing Eclipse documentation. You can navigate through each "book" by section/header or by simply searching via the Search field. You can also bookmark sections in each book and access them through the Bookmarks tab.
The Workbench User Guide documents all facets of the Eclipse user interface extensively. It contains very low-level information on the Eclipse workbench, perspectives, and different concepts useful in understanding how Eclipse works. The Workbench User Guide is an ideal resource for users with little to intermediate experience with Eclipse or IDEs in general. This documentation plug-in is installed by default.
The Eclipse help system also includes a dynamic help feature. This feature opens a new window in the workbench that displays documentation relating to a selected interface element. To activate dynamic help, navigate to Help > Dynamic Help.

The rightmost window in Figure 1.6, “Dynamic Help” displays help topics related to the Outline view, which is the selected user interface element.

## 1.3.  Development Toolkits

Red Hat Enterprise Linux 6 supports the primary Eclipse development toolkits for C/C++ (CDT) and Java (JDT). These toolkits provide a set of integrated tools specific to their respective languages. Both toolkits supply Eclipse GUI interfaces with the required tools for editing, building, running, and debugging source code.
Each toolkit provides custom editors for their respective language. Both CDT and JDT also provide multiple editors for a variety of file types used in a project. For example, the CDT supplies different editors specific for C/C++ header files and source files, along with a Makefile editor.
Toolkit-supplied editors provide error parsing for some file types (without requiring a build), although this may not be available on projects where cross-file dependencies exist. The CDT source file editor, for example, provides error parsing in the context of a single file, but some errors may only be visible when a complete project is built. Other common features among toolkit-supplied editors are colorization, code folding, and automatic indentation. In some cases, other plug-ins provide advanced editor features such as automatic code completion, hover help, and contextual search; a good example of such a plug-in is libhover, which adds these extended features to C/C++ editors (refer to Section 2.2.2, “libhover Plug-in” for more information).
User interfaces for most (if not all) steps in creating a project's target (inary, file, library, etc) are provided by the build functionalities of each toolkit. Each toolkit also provides Eclipse with the means to automate as much of the build process as possible, helping you concentrate more on writing code than building it. Both toolkits also add useful UI elements for finding problems in code preventing a build; for example, Eclipse sends compile errors to the Problems view. For most error types, Eclipse allows you to navigate directly to an error's cause (file and code segment) by simply clicking on its entry in the Problems view.
As is with editors, other plug-ins can also provide extended capabilities for building a project — the Autotools plug-in, for example, allows you to add portability to a C/C++ project, allowing other developers to build the project in a wide variety of environments (for more information, refer to Section 5.3, “Autotools”).
For projects with executable/binary targets, each toolkit also supplies run/debug functionalities to Eclipse. In most projects, "run" is simply executed as a "debug" action without interruptions. Both toolkits tie the Debug view to the Eclipse editor, allowing breakpoints to be set. Conversely, triggered breakpoints open their corresponding functions in code in the editor. Variable values can also be explored by clicking their names in the code.
For some projects, build integration is also possible. With this, Eclipse automatically rebuilds a project or installs a "hot patch" if you edit code in the middle of a debugging session. This allows a more streamlined debug-and-correct process, which some developers prefer.
The Eclipse Help menu provides extensive documentation on both CDT and JDT. For more information on either toolkit, refer to the Java Development User Guide or C/C++ Development User Guide in the Eclipse Help Contents.

## Chapter 2. The Eclipse Integrated Development Environment (IDE)

The entire user interface in Figure 2.1, “Eclipse User Interface (default)” is referred to as the Eclipse workbench. It is generally composed of a code Editor, Project Explorer window, and several views. All elements in the Eclipse workbench are configurable, and fully documented in the Workbench User Guide (Help Contents). Refer to Section 2.2, “Useful Hints” for a brief overview on customizing the user interface.
Eclipse features different perspectives. A perspective is a set of views and editors most useful to a specific type of task or project; the Eclipse workbench can contain one or more perspectives. Figure 2.1, “Eclipse User Interface (default)” features the default perspective for C/C++.
Eclipse also divides many functions into several classes, housed inside distinct menu items. For example, the Project menu houses functions relating to compiling/building a project. The Window menu contains options for creating and customizing perspectives, menu items, and other user interface elements. For a brief overview of each main menu item, refer to Reference > C/C++ Menubar in the C/C++ Development User Guide or Reference > Menus and Actions in the Java Development User Guide.
The following sections provide a high-level overview of the different elements visible in the default user interface of the Eclipse integrated development environment (IDE).

## 2.1. User Interface

The Eclipse workbench provides a user interface for many features and tools essential for every phase of the development process. This section provides an overview of Eclipse's primary user interface.

Figure 2.1, “Eclipse User Interface (default)” displays the default workbench for C/C++ projects. To switch between available perspectives in a workbench, press Ctrl+F8. For some hints on perspective customization, refer to Section 2.2, “Useful Hints”. The figures that follow describe each basic element visible in the default C/C++ perspective.

The Editor is used to write and edit source files. Eclipse can autodetect and load an appropriate language editor (e.g. C Editor for files ending in .c) for most types of source files. To configure the settings for the Editor, navigate to Window > Preferences > language (e.g. Java, C++) > Code Style.

The Project Explorer View provides a hierarchical view of all project resources (binaries, source files, etc.). You can open, delete, or otherwise edit any files from this view.
The button in the Project Explorer View allows you to configure whether projects or working sets are the top-level items in the Project Explorer View. A working set is a group of projects arbitrarily classified as a single set; working sets are handy in organizing related or linked projects.

The Outline window provides a condensed view of the code in a source file. It details different variables, functions, libraries, and other structural elements from the selected file in the Editor, all of which are editor-specific.

Some functions and plugged-in programs in Eclipse send their output to the Console view. This view's button allows you to switch between different consoles.

The Tasks view allows you to track specially-marked reminder comments in the code. This view shows the location of each task comment and allows you to sort them in several ways.

Most Eclipse editors track comments marked with //FIXME or //TODO tags. Tracked comments—i.e. task tags—are different for source files written in other languages. To add or configure task tags, navigate to Window > Preferences and use the keyword task tags to display the task tag configuration menus for specific editors/languages.

The Problems view displays any errors or warnings that occurred during the execution of specific actions such as builds, cleans, or profile runs. To display a suggested "quick fix" to a specific problem, select it and press Ctrl+1.

## 2.2. Useful Hints

Many Eclipse users learn useful tricks and troubleshooting techniques throughout their experience with the Eclipse user interface. This section highlights some of the more useful hints that users new to Eclipse may be interested in learning. The Tips and Tricks section of the Workbench User Guide contains a more extensive list of Eclipse tips.

### 2.2.1. The quick access menu

One of the most useful Eclipse tips is to use the quick access menu. Typing a word in the quick access menu will present a list of Views, Commands, Help files and other actions related to that word. To open this menu, press Ctrl+3.

In Figure 2.10, “Quick Access Menu”, clicking Views > Project Explorer will select the Project Explorer window. Clicking any item from the Commands, Menus, New, or Preferences categories to run the selected item. This is similar to navigating to or clicking the respective menu options or taskbar icons. You can also navigate through the quick access menu using the arrow keys.
It is also possible to view a complete list of all keyboard shortcut commands; to do so, press Shift+Ctrl+L.

To configure Eclipse keyboard shortcuts, press Shift+Ctrl+L again while the Keyboard Shortcuts list is open.

To customize the current perspective, navigate to Window > Customize Perspective. This opens the Customize Perspective menu, allowing the visible tool bars, main menu items, command groups, and short cuts to be configured.
The location of each view within the workbench can be customized by clicking on a view's title and dragging it to a desired location.

Figure 2.13, “Customize Perspective Menu” displays the Tool Bar Visibility tab. As the name suggests, this tab allows you to toggle the visibility of the tool bars (Figure 2.14, “Toolbar”).

The following figures display the other tabs in the Customize Perspective Menu:

The Menu Visibility tab configures what functions are visible in each main menu item. For a brief overview of each main menu item, refer to Reference > C/C++ Menubar in the C/C++ Development User Guide or Reference > Menus and Actions in the Java Development User Guide.

Command groups add functions or options to the main menu or tool bar area. Use the Command Group Availability tab to add or remove a Command group. The Menubar details and Toolbar details fields display the functions or options added by the Command group to either Main Menu or Toolbar Area, respectively.

The Shortcuts tab configures what menu items are available under the following submenus:
• File > New
• Window > Open Perspective
• Window > Show View

### 2.2.2. libhover Plug-in

The libhover plug-in for Eclipse provides plug-and-play hover help support for the GNU C Library and GNU C++ Standard Library. This allows developers to refer to existing documentation on glibc and libstdc++ libraries within the Eclipse IDE in a more seamless and convenient manner via hover help and code completion.
For C++ library resources, libhover needs to index the file using the CDT indexer. Indexing parses the given file in context of a build; the build context determines where header files come from and how types, macros, and similar items are resolved. To be able to index a C++ source file, libhover usually requires you to perform an actual build first, although in some cases it may already know where the header files are located.
The libhover plug-in may need indexing for C++ sources because a C++ member function name is not enough information to look up its documentation. For C++, the class name and parameter signature of the function is also required to determine exactly which member is being referenced. This is because C++ allows different classes to have members of the same name, and even within a class, members may have the same name but with different method signatures.
In addition, C++ also has type definitions and templated classes to deal with. Such information requires parsing an entire file and its associated include files; libhover can only do this via indexing.
C functions, on the other hand, can be referenced in their documentation by name alone. As such, libhover does not need to index C source files in order to provide hover help or code completion. Simply choose an appropriate C header file to be included for a selection.

#### 2.2.2.1.  Setup and Usage

Hover help for all installed libhover libraries is enabled by default, and it can be disabled per project. To disable or enable hover help for a particular project, right-click the project name and click Properties. On the menu that appears, navigate to C/C++ General > Documentation. Check or uncheck a library in the Help books section to enable or disable hover help for that particular library.

Disabling hover help from a particular library may be preferable, particularly if multiple libhover libraries overlap in functionality. For example, the newlib library (whose libhover library plug-in is supported in Red Hat Enterprise Linux 6) contains functions whose names overlap with those in the GNU C library (provided by default); having libhover plugins for both newlib and glibc installed would mean having to disable one.
When multiple libhover libraries libraries are enabled and there exists a functional overlap between libraries, the Help content for the function from the first listed library in the Help books section will appear in hover help (i.e. in Figure 2.18, “Enabling/Disabling Hover Help”, glibc). For code completion, libhover will offer all possible alternatives from all enabled libhover libraries.
To use hover help, simply hover the mouse over a function name or member function name in the C/C++ Editor. After a few seconds, libhover will display library documentation on the selected C function or C++ member function.

To use code completion, select a string in the code and press Ctrl+Space. This will display all possible functions given the selected string; click on a possible function to view its description.

## Chapter 3. Collaborating

Effective revision control is essential to all multi-developer projects. It allows all developers in a team to create, review, revise, and document code in a systematic and orderly manner. Red Hat Enterprise Linux 6 supports three of the most popular open-source revision control systems: CVS, SVN, and Git. The tools for these revision control systems provide access to a wide range of publically available open-source code, as well as the capability to set up individual internal code repositories.
The following section provides a brief overview and references to relevant documentation for each tool.

## 3.1. Concurrent Versions System (CVS)

Concurrent Versions System (CVS) is a centralized version control system based on RCS format with a client-server architecture. It was the first version control system and the predecessor for Subversion (SVN).

### 3.1.1. CVS Overview

This section discusses the various elements of CVS, both the good and the bad.
CVS was developed when network connectivity was unreliable and would often drop out. This meant that if several files were committed at once and the network dropped out, the commit would fail. This can still occur now if a network is unreliable but is less common with modern networking infrastructure. If it happens, the CVS administrator has two options to resolve the problem. The first is to use the admin command to remove stall locked files and back out the changed files. The second option is to reissue the commit command.
CVS uses one central location for making back-ups, which is useful for an unstable network. It allows the enforcement of a commit policy through manually prepared triggers (automated tests, builds, Access Control Lists (ACLs), integration with a bug tracking system) due to centralized architecture. This offers one central location for making back-ups.
To create more detailed commits to the backup, CVS can also expand keywords that are marked by the at-sign (@) to record commit details (committer name, commit message, commit time, for example) into a committed file.
In order to keep track of these commits, CVS uses a server to track the changes for each file separately and in reverse time order. By doing so, the latest version is stored directly and can be retrieved quickly, where older versions must be recomputed by the server. Each changed, committed file is tracked separately with an independent revision identifier. This can make it difficult to discover which files have been changed by the commit when multiple changed files are committed. To counter this, users need to tag the repository state whenever a need exists to refer back and view the changes.
The CVS repository can be accessed by two methods. If the repository is on the same machine as the client (:local: access method) then the client spawns the server on its behalf. If the repository is on a remote machine, the server can be started with rsh/SSH (CVS_RHS environment variable) by a client or by an inet daemon (/etc/xinetd.d/cvs) and different authentication methods (:gserver: access method integrates Kerberos authentication, for example) can be used.
Finally, for security a client-server approach is used with CVS. This means that the client is dependent on connectivity to the server and cannot perform any operation (committing, or reading the commit log) without permission to access the server.

### 3.1.2. Typical scenario

This is a sequence of commands demonstrating CVS repository creation in the $CVSROOT directory (using an absolute path to signal :local: access method), importing sources from $SOURCES, checking them out from the repository into $WORKDIR, modifying some files, and committing the changes. ###### Procedure 3.1. Using CVS 1. Initialize CVS storage. $ mkdir "$CVSROOT"$ cvs -d "$CVSROOT" init  This creates the CVSROOT subdirectory under $CVSROOT with repositories configuration.
2. Import code from $SOURCES directory into CVS as $REPOSITORY, tagged with $VENDOR_TAG and $RELEASE_TAG with a commit $MESSAGE. $ cd "$SOURCES"$ cvs -d "$CVSROOT" import -m "$MESSAGE" "$REPOSITORY" \ "$VENDOR_TAG" "$RELEASE_TAG"  The $SOURCES content should be imported into CVS under $CVSROOT/$REPOSITORY. It is possible to have more repositories in one CVS storage, though this example just uses the one. The $VENDOR_TAG and $RELEASE_TAG are tags for implicit repository branches.
3. Different developers can now check the code out into $WORKDIR. $ cd "$WORKDIR"$ cvs -d "$CVSROOT" checkout "$REPOSITORY"


## Check out directory

Do not check out into the original $SOURCES. This could cause data corruption on the client side and CVS will print errors on various CVS invocations. 4. The latest version of the CVS repository has been transfered into the $REPOSITORY subdirectory. The developer can also check out multiple repositories from one server.
$cd$REPOSITORY

5. To schedule adding a new $FILE use: $ vi "$FILE"$ cvs add "$FILE"  6. The developer can modify an $EXISTING_FILE.
$vi "$EXISTING_FILE"

7. Finally, the developer can commit these changes with a $COMMIT_MESSAGE. $ cvs commit -m "$COMMIT_MESSAGE"  It is possible to export the $CVSROOT value as a CVSROOT environment variable and the cvs tool will respect it. This can free the developer from needing to repetitively supply the -d "$CVSROOT" option. The value is stored in the CVS helper subdirectory at initial check-out, and the CVS tool takes the value from there automatically. ### 3.1.3. CVS Documentation The CVS manual page can be accessed with man cvs. There is also a local FAQ page located in /usr/share/doc/cvs-*/FAQ. CVS information pages are available at http://ximbiot.com/cvs/manual/. The CVS home page is located at http://www.nongnu.org/cvs/. ## 3.2. Apache Subversion (SVN) Subversion is a version control system that manages files and directories, the changes made to them, and can recover and examine them in case of a fault. It was created to match CVS's features and preserve the same development model, and to address any problems often encountered with CVS. This allowed CVS users to convert to SVN with minimal effort. This section will cover the installation of SVN and provide details on the everyday uses of SVN. ### 3.2.1. Installation SVN can be installed with a binary package, directly from source code, or from the console. The easiest way to install SVN would be through the console with the command yum install subversion. Selecting this option ensures that only Red Hat certified packages are used and removes the need to manually update them. Finally, SVN can be installed from source code, though this can be quite complex. From the SVN website, download the latest released source code and follow the instructions in the install file. ### 3.2.2. SVN repository In order to begin using SVN, first a new repository needs to be created. SVN has no way to determine the difference between projects; it is up to the user to administer the file tree and place the project in separate directories as they prefer. Use the following commands to create the repository: # mkdir /var/svn # svnadmin create /var/svn/repos # ls /var/svn/repos/ conf db format hooks locks README.txt  This command will create the new directory /var/svn/repos with the required database files. The SVN repository is accessed with a URL. Usually these use the standard syntax of http:// but it is not limited by this. It also accepts the following URL forms: file:/// Direct repository access (on local disk) http:// Access with WebDAV protocol to Subversion-aware Apache server https:// Same as http:// but with SSL encryption svn:// Access via custom protocol to an svnserver server svn+ssh:// Same as svn:// but through an SSH tunnel. ## Spaces in the URL If the URL contains spaces place quotation marks around it to ensure the shell treats it as a single argument. Otherwise the URL will be invalid. ### 3.2.3. Importing Data Assuming that a project consisting of multiple files has already been created, organize them so that they are all in one directory. It is recommended that you use three top-level directories named branches, tags, and trunk. This is not required by SVN but it is a popular convention. The trunk directory should contain the projects files, and the branches and tags directories should remain empty. For example: myproject/branches/ myproject/tags/ myproject/trunk foo.c bar.c Makefile Once the information has been organized appropriately it is time to import it into the SVN repository. This is done with the svn import command. For example: $ svn import /path/to/mytree \
http://host.example.com/svn/repo/myproject  \
-m "Initial import"
Adding 	myproject/foo.c
Adding	myproject/bar.c
Adding	myproject/subdir
Adding	myproject/subdir/quux.h

Committed revision 1.
$ As can be seen, SVN creates the required directories based on how the file tree is set up. It can now be viewed at the URL created, or by the command: $ svn list http://host.example.com/svn/repo/myproject

### 3.2.4. Working Copies

Now that the first revision of the project has been checked into the repository, it can be edited and worked on. To do this, a working copy needs to be created. This is done with the svn checkout command. For example:
$svn checkout http://host.example.com/svn/repo/trunk A trunk/README A trunk/INSTALL A trunk/src/main.c A trunk/src/header.h ... Checked out revision 8810.$

A directory with a working copy of the project is now created on the local machine. It is also possible to specify where the local directory a project is checked out to with the following command:
$svn checkout http://host.example.com/svn/repo/trunk my-working-copy If the local directory specified does not exist, SVN will create it. ## .svn subdirectory Every directory in the working copy contains a subdirectory called .svn. Being an administrative directory, it will not usually appear with a list command. This is an important file and should not be deleted or changed. Subversion uses this directory to manage the working copy and tampering with it will cause errors and instability. If the directory is accidentally deleted the best way to fix it is to delete the entire containing directory (a normal system delete, not svn delete) and run svn update from a parent directory. The deleted directory will be recreated, including the missing or changed .svn directory. This can cause a loss of data. Although the working copy is now ready to edit, keep in mind that whenever the file tree changes, these changes must be sent to the repository as well. This is done with a variety of commands. svn add filename Newly created files or directories, including the files they contain, are flagged to be added to the repository. The next commit will add them to the repository where they can be accessed and viewed by all. svn delete filename Files or directories, including the files they contain, are flagged to be deleted from the repository. The next commit will remove them. However, the deleted files can still be accessed in previous revisions through SVN. svn copy filename1 filename2 Creates a new file, filename2, which is an exact copy of filename1. It then schedules filename2 for addition on the next commit. Note that svn copy does not create intermediate directories unless the --parents option is passed. svn move filename1 filename2 This is the same as svn copy filename1 filename2 followed by svn delete filename1. A copy is made, and then filename1 is scheduled to be deleted on the next commit. Note that svn move does not create intermediate directories unless the --parents option is passed. svn mkdir directory This command both creates the specified directory and then schedules it to be added to the repository on the next commit. Sometimes it is impractical to check out an entire working copy in order to do some simple changes. In these circumstances it is possible to perform svn mkdir, svn copy, svn move, and svn delete directly on the repository URL. The downside of using this is that with a working copy the changes can be checked before publishing them to ensure that is actually the way they were intended. ### 3.2.5. Committing changes Once the edits are complete and have been verified to work correctly, it is time to publish them so others can view the changes. For each file in the working copy, SVN records two pieces of information: • The file's working revision that the current working file is based on • A timestamp recording when the local copy was last updated by the repository. Using this information, SVN sorts the working copy on the local system into four categories: Unchanged; current The file in the working directory is unchanged and matches the copy in the repository, meaning no changes have been committed since the initial check out. Both svn commit and svn update will do nothing. Locally changed; current The file in the working directory has been edited but has not yet been committed to the repository, and the repository version has not been changed since the initial checkout. Running svn commit will update the repository with the changes in the working directory; running svn update will do nothing. Unchanged; out of date The file in the working directory has not been edited, but the version in the repository has, meaning that the working copy is now out of date. Running svn commit will do nothing; running svn update will merge the changes in the repository with the local working copy. Locally changed; out of date The file in both the working directory and the repository has been changed. If svn commit is run first, an 'out-of-date' error will occur. Update the file first. Running svn update will attempt to merge the changes in the repository with those on the working copy. If there are conflicts SVN will provide options for the user to decide on the best course of action to resolve them. Running svn status will display all of the files in the working tree that do not match the current version in the repository, coded by a letter. ? item The file is not recognized by SVN; that is it is in the working copy, but has not yet been added to the repository, or been scheduled for any action. A item The file is scheduled for addition to the repository and will be added on the next commit. C item The file is in conflict with a change made on the repository. This means that someone has edited and committed a change to the same section of the file currently changed in the working copy, and SVN does not know which is 'correct'. This conflict must be resolved before the changes are committed. D item The file is scheduled for deletion on the next commit. M item The file has been modified and the changes will be updated on the next commit. If the --verbose (-v) is passed with svn status, the status of every item in the working copy will be displayed, even those that have not been changed. For example: $ svn status -v
44	30	sally	INSTALL
M	44	20	harry	bar.c
44	18	ira	stuff
44	35	harry	stuff/trout.c
D	44	19	ira	stuff/fish.c
44	21	sally	stuff/things
A	 0	 ?	 ?	stuff/things/bloo.h
44	36	harry	stuff/things/gloo.c

Along with the letter codes, this shows the working revision, the revision in which the item was last changed, who changed it, and the item changed respectively .
It can also be useful to see which items have been modified in the repository since the last time a checkout was performed. This is done by passing the --show-updates (-u) with svn status. An asterisk (*) will be displayed between the letter status and the working revision number on any files that will be updated when performing an svn commit.
Another way to view changes made is with the svn diff command. This displays changes in a unified diff format, describing changes as 'snippets' of a file's content where each line is prefixed with a character: a space for no change, a minus sign (-) for a line removed, and a plus sign (+) for an added line.
Occasionally a conflict will occur. SVN provides the three most common responses (postpone, diff-full, and edit) and a fourth option to list all the options and what they each do. The options available are:
(p) postpone
Mark the conflict to be resolved later.
(df) diff-full
Display the differences between the base revision and the conflicted file in unified diff format.
(e) edit
Change merged file in an editor.
(r) resolved
Accept the merged version of the file.
(mf) mine-full
Accept my version of the entire file, ignoring the most recent changes in the repository.
(tf) theirs-full
Accept their version of the entire file, ignoring the most recent changes in the local working copy.
(l) launch
Launch an external tool to resolve conflict (this requires set up of the chosen external tool beforehand).
(h) help
Displays the list of options as detailed here.
Finally, provided the project has been changed locally and any conflicts have been resolved, the changes can be successfully committed with the svn commit command, appending the option -m:
$svn commit filename -m "Fixed a typo in filename" Sending filename Transmitting file data . Committed revision 57.$

The most updated version is now available for anyone with access to the repository to update their versions to the newest copy.

### 3.2.6. SVN Documentation

The command svn --help provides information on the available commands to be used in conjunction with SVN and svn subcommand --help provides more detailed information on the specified subcommand.
The official SVN book is available online at http://svnbook.red-bean.com/
The official SVN website is located at http://subversion.apache.org/

## 3.3. Git

Git is a version control system that was not written to improve on CVS and SVN but rather in retaliation to them. Git was created with four design points in mind:
1. Not like CVS and SVN. Torvalds, the creator of Git, does not like these programs and wanted to make something that was unlike them.
2. Support a BitKeeper-like workflow. The way a project is managed ideally follows the same process as BitKeeper, while keeping its own design and not becoming a BitKeeper clone.
3. Strong safeguards against accidental or malicious corruption.
4. Very high performance.
To accomplish this, Git approaches how it handles data differently to its predecessors.
This section will go through the most common processes in a day's use of Git.
Previously the version controls covered (CVS and SVN) treated data as changes to a base version of each file. Instead, Git treats its data changes as separate snapshots of what the files look like and stores a reference to that file (though if the file remains unchanged, Git will simply store a link to the previous identical version rather than copy another file). This creates a kind of new mini-filesystem. The image below compares these concepts visually:

Git is particularly fast, something that is aided by not needing to constantly connect to a remote repository. The snapshot nature of Git and how all versions are stored on the local file system means that nearly everything can be done without connecting to any kind of network and the history of the project is available locally.
To fulfill Torvalds' integrity requirement, everything in Git is check-summed before being stored and then referred to by that check-sum. This means the contents cannot be changed without Git's knowledge and information cannot be lost in transit or corrupted. A SHA-1 hash mechanism (a forty-character hexadecimal sting) is used for this.
In addition, there is very little in Git that cannot be undone. This is aided by the three main states a file can reside in.
Committed
Data is safely stored on the local database, and unchanged.
Modified
The file has been changed but not yet committed to the database.
Staged
A modified file has been marked to be committed in its current version.

### 3.3.1. Installation

Git can be installed either from source or from the console. If the user is confident enough then the recommendation is to install from source, as the binary installers don't always have the most up-to-date version available.
To install Git from source code, use the following procedure:
###### Procedure 3.2. To install Git from source code
1. Install the libraries Git depends on: curl, zlib, openssl, expat, and libiconv.
$sudo yum install curl-devel expat-devel gettext-devel \ openssl-devel zlib-devel gcc  2. Download the latest snapshot from the Git web site, located here: http://git-scm.com/download. 3. Compile and install. $ tar -zxf git-1.7.6.1.tar.gz
$cd git-1.7.2.2$ make prefix=/usr/local
$sudo make prefix=/usr/local install  4. It is now possible to get updates for Git, from Git. $ git clone git://git.kernel.org/pub/scm/git/git.git
Installing Git with a binary installer from the console is as simple as using the following command.
$yum install git ### 3.3.2. Initial Setup After installing there are a few steps to personalize Git and get it ready for use. These only need to be set up once and Git will remember the settings, however if they need to be changed in the future just run the commands again. These changes are made by altering variables stored in three different places: 1. The /etc/gitconfig file contains variables for every user on the system and all their repositories. It holds the base settings and passing --system to git config sets it to read and write from this file. 2. The ~/.gitconfig file is specific to the user. Passing --global tells Git to read and write to this file, overriding the settings made in the first point. 3. The config file in the Git directory (.git/config) of the repository currently being used. This is specific to this repository only and override the settings in both the first and the second point. Before the first commit, enter some details into Git by supplying the name and email address that will appear with change. For example, if the user's name is John Q. Smith, use the following commands: $ git config --global user.name "John Smith"
$git config --global user.email "jsmith@example.com"  As explained above, by passing the --global option this only needs to be set once, but can be overridden for specific repositories. By default, whenever an editor is needed, Git launches Vi or Vim. However, if this is not preferred it is possible to change this to another editor. To do so, use the following command: git config --global core.editor EditorName The diff tool is often used to view the changes in various files, useful for double checking things before committing them. Git currently accepts the following meld diff tool. Use the following command to set the preferred diff tool: $ git config --global merge.tool DiffTool
Finally, it is useful to check these settings to ensure they are correct. To do this run:
$git config --list user.name=John Smith user.email=jsmith@example.com  If there are different settings in different files, Git will list them all, with the last value for the active one. It is also possible for Git to check the specific response to a variable by using the git config {key} command. For example: $ git config user.name
John Smith

### 3.3.3. Git repository

The Git repository is where the metadata and object database is stored for a project. This is where the project is pulled from in order to get a local clone of a repository on a local system.
There are two options for obtaining a Git repository. The first is for when a directory already exists and there is the need to initialize a Git repository. The second is cloning a repository that already exists.
To clone an existing repository (for example, to contribute to) then run the following command:
$git clone git://location/of/git/repository.git Note that the command is git clone as opposed to git checkout as it might be for a version control system similar to CVS and SVN. This is because Git receives a copy of every file in the project's entire history, as opposed to only the most recent files as with other version control systems. The above command creates a directory where the name is the last component of the URL, but with any .git suffix removed. However, the clone command can use any other name simply by appending the desired directory name to the end: $ git clone git://location/of/git/repository.git my_git_repo
Finally, even though this command uses the git:// protocol, it is also possible to use http:// or https:// as appropriate.
To create a new Git repository ready to create data for, first navigate to the project's directory and type:
$git init This creates a skeleton of a Git repository, containing all the necessary files ready for content to be created and added. Now that either a skeleton Git repository is set up or a local clone copied and ready on the local system it is time to look at the rest of the Git cycle. This image shows how the Git cycle works and will be explained in further detail in the following sections. ### 3.3.4. Untracked files Untracked files are those that Git does not recognize. This will occur if a file is newly created or for all files in a new project. The status of a file can be shown with the git status command. For a newly started project there will be files in the untracked status. $ git status
# On branch master
# Untracked files:
#	(use "git add <file>..." to include in what will be committed)
#		filename
nothing added to commit but untracked files present (use "git add" to track)

As the status helpfully says, the files will not be included unless Git is told to include them with the git add command.
$git add filename The command git add filename will add that specific file first to the unmodified section. Use git add . to add all files in the current directory (including any sub-directories), or for example git add *.[ch] to add all .c and .h files in the current directory. ### 3.3.5. Unmodified files The unmodified status is where those files that have not changed are kept. Git is aware of them and is tracking them so that when an edit is made they are transferred to the modified status. Also, after a commit, the files are returned to this state. It is also possible to remove files from this state to stop Git from tracking them. This will remove them locally as well. To do so run: $ git rm filename
rm 'filename'
$git status # On branch master # # Changes to be committed: # (use "git reset HEAD <file>..." to unstage) # # deleted: filename #  ## Removing a file Note, that if a file is unmodified, git rm filename will remove the entire file. It is only when a file has uncommitted changes that git rm filename will give a diagnostic and not remove it. To remove a file despite the uncommitted changes, use the  --force or -f option. To stop Git from tracking a file without removing it locally, use the --cached option, then commit the removal. $ git rm --cached filename
$git commit -m'remove file message'  ### 3.3.6. Modified Status A copy is on the local system ready to edit. As soon as any changes are made Git recognizes the file as modified and moves it to the modified status. Running git status will show this: $ git status
# On branch master
# Changed but not updated:
#	(use "git add <file>..." to update what will be committed)
#
#		modified:	filename
#

The file has been changed but as of yet it will not be committed (after all, more changes can still be made and it may not be ready to be committed). As the output helpfully points out, using the git add filename command again will push the modified file to the staged status, ready to be committed.
$git add filename$ git status
# On branch master
# Changes to be committed:
#	(use "git reset HEAD <file>..." to unstage)
#
#		new file:	filename
#

This process can become a little more complex if a staged file needs to have one final edit before it is committed as it will appear in both the staged status and the modified status. If this occurs then a status will look like this:
$git status # On branch master # Changes to be committed: # (use "git reset HEAD <file>..." to unstage) # # modified: filename1 # # Changed but not updated: # (use "git add <file>..." to unstage) # # modified: filename1 #  This is where the Git snapshots are highlighted; there is a snapshot of a file ready to be committed and another snapshot in the modified status. If a commit is run then only the snapshot of the staged status will be committed, not the corrected version. Running git add again will resolve this and the modified snapshot of the file will merge with the snapshot on the staged status, ready to commit the new changes. ### 3.3.7. Staged files The staged status is where the snapshot of all files that are ready to be committed reside. All files in this status will be committed when the command is given. #### 3.3.7.1. Viewing changes Before committing the snapshots on the staged status, it is a good idea to check the changes made to ensure that they are acceptable. This is where the command git diff comes in. $ git diff
diff --git a/filename b/filename
index 3cb747f..da65585 100644
--- a/filename
+++ b/filename
@@ -36,6 +36,10 @@ def main
@commit.parents[0].parents[0].parents[0]
end

+	some code
+		some more code
+	a comment
+	another change
-	a mistake
Running the git diff command with no parameters, as above, compares the working directory to what is in the staged status, displaying changes made but not yet committed.
It is also possible to compare the changes between the staged status and what the last commit was by using the --cached option.
$git diff --cached diff --git a/filename b/filename new file mode 100644 index 0000000..03902a1 -- /dev/null +++ b/filename @@ -0,0 +1,5 @@ +file + by name1, name2 + http://path/to/file + + added information to file ## Alternate command In versions 1.6.1 and later of Git it is also possible to use the --staged option instead of --cached. #### 3.3.7.2. Committing changes After checking that all the staged files are correct and ready, it is time to commit the changes. $ git commit
The above command will launch the chosen editor set in the initial setup, or if this was not set up it defaults to Vim.
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch master
# Changes to be committed:
#	(use "git reset HEAD <file>..." to unstage)
#
#		new file:	filename2
#		modified:	filename1
~
~
~
".git/COMMIT_EDITMSG" 10L, 283C

As can be seen, the last status report is also included in the editor, though because of the hash (#) it will not be visible in the actual commit log. For more information on what is being committed, pass the -v option with git commit. The commit message can be entered here, or it can be entered in the command line with the -m option:
$git commit -m "commit message" [master]: created 4156dc4f: "commit message" 2 files changed, 3 insertions(+), 1 deletions (-) create mode 100644 filename The commit message provides some information: the branch committed to (master in this case), what SHA-1 checksum the commit has (4156dc4f), how many files were changed, and some statistics about what was changed within them. ## Skipping the staging status It is possible to skip the staging area which can be useful, but holds the risk of committing something that was not ready to be committed yet. This is done by passing the -a option with git commit. $ git status
# On branch master
#
# Changed but not updated:
#
#	modified:	filename
#
$git commit -a -m 'commit message' [master 16e15c7] commit message 1 files changed, 5 insertions(+), 2 deletions(-)  ### 3.3.8. Remote repositories In order to share a project with the world, it needs to be pushed to a remote repository, hosted on a network or on the internet. To be able to push to a remote directory, first one must be made. To do so, run the command git add [shortname] [URL] $ git remote add shortname git://path/to/new/repo
The shortname can now be used in lieu of the URL when referring to the remote repository.
Now a repository is added it is possible to print a list of remote repositories. This is done with the git remote command, passing the -v option to display the associated URL as well as just the shortname if desired. Even without adding a new remote repository, if the project was cloned it will list at least the repository it was cloned from.
$git remote -v repo-name git://path/to/new/remote-repository origin git://path/to/original/remote-repository If even this is not enough information running the git show [remote-repository] will list the URL as well as the branches Git is tracking for this particular repository. In order to fetch data from remote repositories (for example, if someone working on the project has pushed new information to them), use the following command: $ git fetch [remote-name]
This pulls down any and all information from this particular remote host that differs from what is on the local copy. Alternatively, running git pull will do the same from the repository the original copy was cloned from.
In order to share a project with a wider audience it needs to be pushed to a remote repository.
$git push remote-repository branch-name This command pushes the specified branch to the specified repository, but only if the user has write access. In the case of a conflict, pull the new work down first to incorporate it into the local version before pushing it to the remote repository. Finally to rename a repository, run the git remote rename original-name new-name. Keep in mind that this will also change the remote branch names as well. Removing a repository is similar: git remote rm remote-name. ### 3.3.9. Commit logs After working with a repository for some time, making several changes and commits, a need may arise to view the logs of these changes. This is done with the git log command. When this is run with no arguments, it lists each commit in reverse chronological order, presenting the time and date of the commit, the SHA-1 checksum, the author's name and email, and the commit message. It is possible to include the diff report in these logs, and limit the output by a set number of entries. For example, running git log -p -2 will list the normal log information in addition to the diff reports for the two most recent entries. To include some statistics at the end of each commit entry, use the git log --stat. This command will include a list of modified files, how many files were changed, and how many lines were added and removed, followed by a summary of this information, after the commit message. Along with these useful options, there are a number of others which can be passed with this command: --shortstat Similar to the --stat option, but this displays only the changed, insertions, and deletions in a commit. --name-only Lists only the files modified after the commit information. --name-status Lists the files modified along with the changed, insertions, and deletions. --abbrev-commit Only displays the first few characters of the SHA-1 checksum, instead of all forty. --relative-date Displays the date relative to the current date. For example, instead of reading Tue July 10:53:11 2011 -0700, it will print 2 weeks ago. --graph Display Prints an ASCII graph of the branch and merge history beside the log output. --since=[date] Prints the log since a specified date; that is, everything after the date. The date can be entered in a variety of different formats, be it a specific date (2010-08-23, for example) or a relative date ("1 year 3 days 4 minutes ago", for example). --until=[date] Similar to the --since option, this will print the log up until the specified date; that is, everything before the date. --author name Lists only those commits with the specified name in the author field. --committer name Lists only those commits with the specified name in the committer field. ### 3.3.10. Fixing problems There may come a time when mistakes are made and something needs to be removed or undone. This section will cover some of the ways these errors can be fixed. ## Data loss This is one of the few areas in Git where data can be lost forever. If an undo is performed and then discovered it should not have been, it is highly likely that it is now impossible to recover the lost data. Proceed with caution. This occurs most often when a commit is pushed too early, committing something that is not yet ready, or making a mistake in the commit message. This can be fixed by committing over the top of the latest commit using the --amend option. $ git commit --amend
If the files on the staged status are different from those in the latest commit, the commit will run normally except it will override the original. If the files are the same, then the option will be provided to change the commit message, again, overriding the previous commit.
It is also possible to unstage a staged file. This can sometimes be required if git add * was used when the intention was to have two (or more) separate commits. The git status command provides a hint on how to do this as well:
#	(use "git reset HEAD <file>..." to unstage)
So to follow its advice, use the command git reset HEAD filename and the file is now reverted to the modified status rather than the staged status.
To revert a file back to what it looked like at the last commit, the git status command comes to the rescue again in the unstaged status:
#	(use "git checkout -- <file>..." to discard changes in working directory)
Following these instructions with the git checkout -- filename reverts the file. To reiterate the above warning however, this will cause data loss; only use it when it is certain this version of the file is no longer wanted.

### 3.3.11. Git documentation

The main Git man page can be viewed with man git. This also provides the commands to access other man pages such as gittutorial(7), Everyday Git[1], and gitglossary(7).
The official Git homepage can be accessed at http://git-scm.com/ where more documentation is available and can be downloaded.
The following is a list of websites containing more detailed Git information.

## Chapter 4. Libraries and Runtime Support

Red Hat Enterprise Linux 6 supports the development of custom applications in a wide variety of programming languages using proven, industrial-strength tools. This chapter describes the runtime support libraries provided in Red Hat Enterprise Linux 6.

## 4.1. Version Information

The following table compares the version information for runtime support packages in supported programming languages between Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 5, and Red Hat Enterprise Linux 4.
This is not an exhaustive list. Instead, this is a survey of standard language runtimes, and key dependencies for software developed on Red Hat Enterprise Linux 6.
###### Table 4.1. Language and Runtime Library Versions
Package Name Red Hat Enterprise 6 Red Hat Enterprise 5 Red Hat Enterprise 4
glibc 2.12 2.5 2.3
libstdc++ 4.4 4.1 3.4
boost 1.41 1.33 1.32
java 1.5 (IBM), 1.6 (IBM, OpenJDK, Oracle Java) 1.4, 1.5, and 1.6 1.4
python 2.6 2.4 2.3
php 5.3 5.1 4.3
ruby 1.8 1.8 1.8
httpd 2.2 2.2 2.0
postgresql 8.4 8.1 7.4
mysql 5.1 5.0 4.1
nss 3.12 3.12 3.12
openssl 1.0.0 0.9.8e 0.9.7a
libX11 1.3 1.0
firefox 3.6 3.6 3.6
kdebase 4.3 3.5 3.3
gtk2 2.18 2.10 2.04

## compat-glibc package

The compat-glibc RPM is included with Red Hat Enterprise Linux 6, but it is not a runtime package and therefore not needed for running anything. It is solely a development package, containing header files and dummy libraries for linking. This allows compiling and linking packages to run in older Red Hat Enterprise Linux versions (using compat-gcc-* against those headers and libraries). Running rpm -qpi compat-glibc-* will provide some information on how to use this package.

## 4.2. Compatibility

Compatibility specifies the portability of binary objects and source code across different instances of a computer operating environment. Officially, Red Hat supports current release and two consecutive prior versions. This means that applications built on Red Hat Enterprise Linux 4 and Red Hat Enterprise Linux 5 will continue to run on Red Hat Enterprise Linux 6 as long as they comply with Red Hat guidelines (using the symbols that have been white-listed, for example).
Red Hat understands that as an enterprise platform, customers rely on long-term deployment of their applications. For this reason, applications built against C/C++ libraries with the help of compatibility libraries continue to be supported for seven years, or ten years with an extended subscription.
For further information regarding this, refer to Red Hat Enterprise Linux supported releases accessed at https://access.redhat.com/support/policy/updates/errata/ and the general Red Hat Enterprise Linux compatibility policy, accessed at https://www.redhat.com/f/pdf/rhel/RHEL6_App_Compatibility_WP.pdf.
There are two types of compatibility:
Source Compatibility
Source compatibility specifies that code will compile and execute in a consistent and predictable way across different instances of the operating environment. This type of compatibility is defined by conformance with specified Application Programming Interfaces (APIs).
Binary Compatibility
Binary Compatibility specifies that compiled binaries in the form of executables and Dynamic Shared Objects (DSOs) will run correctly across different instances of the operating environment. This type of compatibility is defined by conformance with specified Application Binary Interfaces (ABIs).

### 4.2.1. API Compatibility

Source compatibility enables a body of application source code to be compiled and operate correctly on multiple instances of an operating environment, across one or more hardware architectures, as long as the source code is compiled individually for each specific hardware architecture.
Source compatibility is defined by an Application Programming Interface (API), which is a set of programming interfaces and data structures provided to application developers. The programming syntax of APIs in the C programming language are defined in header files. These header files specify data types and programmatic functions. They are available to programmers for use in their applications, and are implemented by the operating system or libraries. The syntax of APIs are enforced at compile time, or when the application source code is compiled to produce executable binary objectcode.
APIs are classified as:
• De facto standards ­ not formally specified but implied by a particular implementation.
• De jure standards ­ formally specified in standards documentation.
In all cases, application developers should seek to ensure that any behavior they depend on is described in formal API documentation, so as to avoid introducing dependencies on unspecified implementation specific semantics or even introducing dependencies on bugs in a particular implementation of an API. For example, new releases of the GNU C library are not guaranteed to be compatible with older releases if the old behavior violated a specification.
Red Hat Enterprise Linux by and large seeks to implement source compatibility with a variety of de jure industry standards developed for Unix operating environments. While Red Hat Enterprise Linux does not fully conform to all aspects of these standards, the standards documents do provide a defined set of interfaces, and many components of Red Hat Enterprise Linux track compliance with them (particularly glibc, the GNU C Library, and gcc, the GNU C/C++/Java/Fortran Compiler). There are and will be certain aspects of the standards which are not implemented as required on Linux.
A key set of standards that Red Hat seeks to conform with are those defined by the Austin Common Standards Revision Group (“The Austin Group”).
The Austin Group is a working group formed in 1998 with the aim of unifying earlier Unix standardization efforts including ISO/IEC 9945­1 and 9945­2, IEEE Standards 1003.1 and 1003.2 (POSIX), and The Open Group's Single Unix Specification. The goal of The Austin Group is to unify the POSIX, ISO, and SUS standards into a single set of consistent standards. The Austin Group includes members from The Open Group, ISO, IEEE, major Unix vendors, and the open source community. The combined standards issued by The Austin Group carry both the IEEE POSIX designation and The Open Group's Technical Standard designation, and in the future the ISO/IEC designation. More information on The Austin Group is available at http://www.opengroup.com/austin.
Red Hat Enterprise Linux characterizes API compatibility four ways, with the most compatible APIs scored with the smallest number in the following list:
1. No changes. Consumer should see no visible changes.
2. Additions only. New structures, fields, header files, and exported interfaces may be added. Otherwise no visible changes allowed.
3. Additions and Deprecations allowed. Structs, headers, fields, exported interfaces may be marked as deprecated or if previously marked as deprecated the headers, fields, exported interfaces, etc may be removed. Deprecated items may still exist as part of a compatibility layer in versioned libraries for ABI compatibility purposes, but are no longer available in APIs.
4. Anything goes. No guarantees whatsoever are made.
In the following sections, these API classification levels will be detailed for select components of Red Hat Enterprise Linux.

### 4.2.2. ABI Compatibility

Binary compatibility enables a single compiled binary to operate correctly on multiple instances of an operating environment that share a common hardware architecture (whether that architecture support is implemented in native hardware or a virtualization layer), but a different underlying software architecture.
Binary compatibility is defined by an Application Binary Interface (ABI). The ABI is a set of runtime conventions adhered to by all tools which deal with a compiled binary representation of a program. Examples of such tools include compilers, linkers, runtime libraries, and the operating system itself. The ABI includes not only the binary file formats, but also the semantics of library functions which are used by applications.
Similar to the case of source compatibility, binary compatibility ABIs can be classified into the following:
• De facto standards, which are not formally specified but implied by a particular implementation.
• De jure standards, which are formally specified in standards documentation.
Red Hat Enterprise Linux by and large seeks to implement binary compatibility with a de jure industry standard developed for GNU/Linux operating environments, the Linux Standard Base (LSB). Red Hat Enterprise Linux 6 implements LSB version 4.
Red Hat Enterprise Linux characterizes ABI compatibility four ways, with the most compatible ABIs scored with the smallest number in the following list:
1. No changes made. Consumer should see no changes.
2. Versioned additions only, no removals. New structures, fields, header files, and exported interfaces may be added as long as additional techniques are used to effectively version any new symbols. Applicable mechanisms for versioning external symbols include the use of compiler visibility support (via pragma, annotation, or suitable flag), use of language-specific features, or use of external link maps. Many of these techniques can be combined.
3. Incompatible, but a separate compatibility library is packaged so that previously linked binaries can run without modification. Use is mutually exclusive: either the compatibility package is used, or the current package is used.
4. Anything goes. Incompatible, with no recourse.
In the following sections, these ABI classification levels will be detailed for select components of Red Hat Enterprise Linux.

### 4.2.3. Policy

#### 4.2.3.1. Compatibility Within A Major Release

One of the core goals of the Red Hat Enterprise Linux family of products is to provide a stable, consistent runtime environment for custom application development. To support this goal, Red Hat seeks to preserve application binary compatibility, configuration file compatibility, and data file compatibility for all Red Hat Enterprise Linux 6 package updates issued within a major release. For example, a package update from Red Hat Enterprise Linux 6 Update 1 to Red Hat Enterprise Linux Update 2, or a package update that fixes an identified security vulnerability, should not break the functionality of deployed applications as long as they adhere to standard Application Binary Interfaces (ABIs) as previously discussed.

#### 4.2.3.2. Compatibility Between Major Releases

Red Hat Enterprise Linux also provides a level of compatibility across major releases, although it is less comprehensive than that provided within a major release. With the qualifications given below, Red Hat Enterprise Linux 6 provides runtime compatibility support for applications built for Red Hat Enterprise Linux 5 and Red Hat Enterprise Linux 4.
For example, applications that are are compiled with header files and linked to a particular version of glibc, the GNU C Library, are intended to continue to work with later versions of glibc. For the case of glibc, this is accomplished by providing versioned symbols, whose syntax and semantics are preserved in subsequent releases of the library even if a new, otherwise incompatible implementation is added. For other core system components, such as all 2.x releases of the GTK+ toolkit, backwards compatibility is ensured simply by limiting changes, which preserve the syntax and semantics of the defined APIs. In many cases, multiple versions of a particular library may be installed on a single system at the same time to support different versions of an API. An example is the inclusion of both Berkeley Database (db) version 4.7.25 and a compatibility version 4.3.29 in Red Hat Enterprise Linux 6, each with its own set of headers and libraries.
Red Hat provides compatibility libraries for a set of core libraries. However, Red Hat does not guarantee compatibility across major releases of the distribution for dynamically linked libraries outside of the core library set unless versions of the Dynamic Shared Objects (DSOs) the application expects are provided (either as part of the application package or separate downloads). To ensure compatibility across major releases, application developers are encouraged to limit their dynamically linked library dependencies to those in the core library set, or to provide an independent version of the required non­ core libraries packaged with their application (which in turn depend only on core libraries). As a rule, Red Hat recommends against statically linking libraries into applications. For more information on why we recommend against static linking, see Section 4.2.4, “Static Linking”
Red Hat also reserves the right to remove particular packages between major releases. Red Hat provides a list of deprecated packages that may be removed in future versions of the product in the Release Notes for each major release. Application developers are advised to avoid using libraries on the deprecated list. Red Hat reserves the right to replace specific package implementations in future major releases with alternative packages that implement similar functionality.
Red Hat does not guarantee compatibility of configuration file formats or data file formats between major releases of the distribution, although individual software packages may in fact provide file migration or compatibility support.

#### 4.2.3.3. Building for forward compatibility across releases

Ideally, rebuild and repackage applications for each major release. This allows full advantage of new optimizations in the compiler, as well as new features available in the latest tools, to be taken.
However, there are times when it is useful to build one set of binaries that can be deployed on multiple major releases at once. This is especially useful with old code bases that are not compliant to the latest revision of the language standards available in more recent Red Hat Enterprise Linux releases.
Therefore it is advised to refer to the Red Hat Enterprise Linux 6 Application Compatibility Specification for guidance. This document outlines Red Hat policy and recommendations regarding backwards compatibility, particularly for specific packages.
For example, if you would like to build a package that can be deployed in RHEL4, RHEL5, and RHEL6 with one set of binaries, here are some general guidelines:
• The main point to keep in mind is that you must build on the lowest common denominator. In this case, RHEL4.
• Compatibility libraries must be available in subsequent releases (RHEL5 and RHEL6 in this case). For more details on compatibility libraries, see Section 5.1.4, “Backwards Compatibility Packages”.
Please note, that Red Hat only guarantees this forward compatibility between releases for the past 2 Enterprise Linux releases. That is, building on RHEL4 is guaranteed to work on RHEL5 and RHEL6, provided you have the appropriate compatibility libraries on the latest two releases. Building on RHEL5 is guaranteed to work on RHEL6 and the next release thereafter.

Static linking is emphatically discouraged for all Red Hat Enterprise Linux releases. Static linking causes far more problems than it solves, and should be avoided at all costs.
The main drawback of static linking is that it is only guaranteed to work on the system on which it was built, and even then only until the next release of glibc or libstdc++ (in the case of C++). There is no forward or backward compatibility with a static build. Furthermore, any security fixes (or general-purpose fixes) in subsequent updates to the libraries will not be available unless the affected statically linked executables are re-linked.
A few more reasons why static linking should be avoided are:
• Larger memory footprint.
• Slower application startup time.
• Reduced glibc features with static linking.
• Dynamic loading of shared objects outside of glibc is not supported.

### 4.2.5. Core Libraries

Red Hat Enterprise Linux maintains a core set of libraries where the APIs and ABIs are preserved for each architecture across major releases (eg between Red Hat Enterprise Linux 5 and 6). This will help developers produce software that is compatible with a variety of Red Hat Enterprise Linux versions. Limit applications to linking against this set of libraries to take advantage of this feature.
The list of core libraries maintained by Red Hat Enterprise Linux includes the following. Each package is annotated with a compatibility number for ABI and ABI. The API numbers correspond to characterizations described in Section 4.2.1, “API Compatibility”. The ABI numbers correspond to characterizations described in Section 4.2.2, “ABI Compatibility”.
###### Table 4.2. Core Library Compatibility
Package Name Files Previous RHEL Version Notes
5 4
API ABI API ABI
glibc libc, libm, libdl, libutil, libcrypt 2 2 3 2 See notes for RHEL 2 and 3.
libstdc++ libstdc++ 2 2 3 2 See notes for RHEL 3.
zlib libz 1 ? 1 ?
ncurses-libs libncurses 1 ? 1 ?
nss libnss3, libssl3 ? ?
gtk2 libgdk-x11-2.0, libgdk_pixbuf-2.0, libgtk-x11-2.0 2 ? ?
glib2 libglib-2.0, libgmodule-2.0, libgthread-2.0, 2 ? ?

If an application can not limit itself to the interfaces of these core libraries, then to ensure compatibility across major releases, the application should bundle the additional required libraries as part of the application itself. In that case, the bundled libraries must themselves use only the interfaces provided by the core libraries.

### 4.2.6. Non-Core Libraries

Red Hat Enterprise Linux also includes a wide range of libraries whose APIs and ABIs are not guaranteed to be preserved between major releases. Compatibility of these libraries is, however, provided within a major release of the distribution. Applications are free to use these non­core libraries, but to ensure compatibility across major releases, application vendors should provide their own copies of these non­core libraries, which in turn should depend only on the core libraries listed in the previous section.
Each package is annotated with a compatibility number for API and ABI. The API numbers correspond to characterizations described in Section 4.2.1, “API Compatibility”. The ABI numbers correspond to characterizations described in Section 4.2.2, “ABI Compatibility”.
###### Table 4.3. Non-Core Library Compatibility
Package Name Files Previous RHEL Version
5 4
API ABI API ABI
boost libboost_filesystem, libboost_threads 4 4 4 4
openssl libssl, libcrypto 4 3 4 4

## 4.3. Library and Runtime Details

### 4.3.1. The GNU C Library

The glibc package contains the GNU C Library. This defines all functions specified by the ISO C standard, POSIX specific features, some Unix derivatives, and GNU-specific extensions. The most important set of shared libraries in the GNU C Library are the standard C and math libraries.
The GNU C Library defines its functions through specific header files, which you can declare in source code. Each header file contains definitions of a group of related facilities; for example, the stdio.h header file defines I/O-specific facilities, while math.h defines functions for computing mathematical operations.

#### 4.3.1.1. GNU C Library Updates

The Red Hat Enterprise Linux 6 version of the GNU C Library features the following improvements over its Red Hat Enterprise Linux 5 version:
• bo_CN
• bo_IN
• shs_CA
• ber_DZ
• ber_MA
• en_NG
• fil_PH
• fur_IT
• fy_DE
• ha_NG
• ig_NG
• ik_CA
• iu_CA
• li_BE
• li_NL
• nds_DE
• nds_NL
• pap_AN
• sc_IT
• tk_TM
• preadv
• preadv64
• pwritev
• pwritev64
• malloc_info
• mkostemp
• mkostemp64
• Added new Linux-specific interfaces, namely:
• epoll_pwait
• sched_getcpu
• accept4
• fallocate
• fallocate64
• inotify_init1
• dup3
• epoll_create1
• pipe2
• signalfd
• eventfd
• eventfd_read
• eventfd_write
• Added new checking functions, namely:
• asprintf
• dprintf
• obstack_printf
• vasprintf
• vdprintf
• obstack_vprintf
• fread
• fread_unlocked
• open*
• mq_open
For a more detailed list of updates to the GNU C Library, refer to /usr/share/doc/glibc-version/NEWS . All changes as of version 2.12 apply to the GNU C Library in Red Hat Enterprise Linux 6. Some of these changes have also been backported to Red Hat Enterprise Linux 5 versions of glibc.

#### 4.3.1.2. GNU C Library Documentation

The GNU C Library is fully documented in the GNU C Library manual; to access this manual locally, install glibc-devel and run info libc. An upstream version of this book is also available here:

### 4.3.2. The GNU C++ Standard Library

The libstdc++ package contains the GNU C++ Standard Library, which is an ongoing project to implement the ISO 14882 Standard C++ library.
Installing the libstdc++ package will provide just enough to satisfy link dependencies (i.e. only shared library files). To make full use of all available libraries and header files for C++ development, you must install libstdc++-devel as well. The libstdc++-devel package also contains a GNU-specific implementation of the Standard Template Library (STL).
For Red Hat Enterprise Linux 4, 5, and 6, the C++ language and runtime implementation has remained stable and as such no compatibility libraries are needed for libstdc++. However, this is not the case for Red Hat Enterprise Linux 2 and 3. For Red Hat Enterprise Linux 2 compat-libstdc++-296 needs to be installed. For Red Hat Enterprise Linux 3 compat-libstdc++-33 needs to be installed. Neither of these are installed by default so need to be added separately.

#### 4.3.2.1.  GNU C++ Standard Library Updates

The Red Hat Enterprise Linux 6 version of the GNU C++ Standard Library features the following improvements over its Red Hat Enterprise Linux 5 version:
• Added support for elements of ISO C++ TR1, namely:
• <tr1/array>
• <tr1/complex>
• <tr1/memory>
• <tr1/functional>
• <tr1/random>
• <tr1/regex>
• <tr1/tuple>
• <tr1/type_traits>
• <tr1/unordered_map>
• <tr1/unordered_set>
• <tr1/utility>
• <tr1/cmath>
• Added support for elements of the upcoming ISO C++ standard, C++0x. These elements include:
• <array>
• <chrono>
• <condition_variable>
• <forward_list>
• <functional>
• <initalizer_list>
• <mutex>
• <random>
• <ratio>
• <regex>
• <system_error>
• <thread>
• <tuple>
• <type_traits>
• <unordered_map>
• <unordered_set>
• Added support for the -fvisibility command.
• __gnu_cxx::typelist
• __gnu_cxx::throw_allocator
For more information about updates to libstdc++ in Red Hat Enterprise Linux 6, refer to the C++ Runtime Library section of the following documents:

#### 4.3.2.2.  GNU C++ Standard Library Documentation

To use the man pages for library components, install the libstdc++-docs package. This will provide man page information for nearly all resources provided by the library; for example, to view information about the vector container, use its fully-qualified component name:
man std::vector
This will display the following information (abbreviated):
std::vector(3)                                                  std::vector(3)

NAME
std::vector -

elements in any order.

SYNOPSIS
Inherits std::_Vector_base< _Tp, _Alloc >.

Public Types
typedef _Alloc allocator_type
typedef __gnu_cxx::__normal_iterator< const_pointer, vector >
const_iterator
typedef _Tp_alloc_type::const_pointer const_pointer
typedef _Tp_alloc_type::const_reference const_reference
typedef std::reverse_iterator< const_iterator >

The libstdc++-docs package also provides manuals and reference information in HTML form at the following directory:
file:///usr/share/doc/libstdc++-docs-version/html/spine.html
The main site for the development of libstdc++ is hosted on gcc.gnu.org.

### 4.3.3. Boost

The boost package contains a large number of free peer-reviewed portable C++ source libraries. These libraries are suitable for tasks such as portable file-systems and time/date abstraction, serialization, unit testing, thread creation and multi-process synchronization, parsing, graphing, regular expression manipulation, and many others.
Installing the boost package will provide just enough libraries to satisfy link dependencies (i.e. only shared library files). To make full use of all available libraries and header files for C++ development, you must install boost-devel as well.
The boost package is actually a meta-package, containing many library sub-packages. These sub-packages can also be installed in an a la carte fashion to provide finer inter-package dependency tracking. The meta-package includes all of the following sub-packages:
• boost-date-time
• boost-filesystem
• boost-graph
• boost-iostreams
• boost-math
• boost-program-options
• boost-python
• boost-regex
• boost-serialization
• boost-signals
• boost-system
• boost-test
• boost-thread
• boost-wave
Not included in the meta-package are packages for static linking or packages that depend on the underlying Message Passing Interface (MPI) support.
MPI support is provided in two forms: one for the default Open MPI implementation [1] , and another for the alternate MPICH2 implementation. The selection of the underlying MPI library in use is up to the user and depends on specific hardware details and user preferences. Please note that these packages can be installed in parallel, as installed files have unique directory locations.
For Open MPI:
• boost-openmpi
• boost-openmpi-devel
• boost-graph-openmpi
• boost-openmpi-python
For MPICH2:
• boost-mpich2
• boost-mpich2-devel
• boost-graph-mpich2
• boost-mpich2-python
If static linkage cannot be avoided, the boost-static package will install the necessary static libraries. Both thread-enabled and single-threaded libraries are provided.

The Red Hat Enterprise Linux 6 version of Boost features many packaging improvements and new features.
Several aspects of the boost package have changed. As noted above, the monolithic boost package has been augmented by smaller, more discrete sub-packages. This allows for more control of dependencies by users, and for smaller binary packages when packaging a custom application that uses Boost.
In addition, both single-threaded and multi-threaded versions of all libraries are packaged. The multi-threaded versions include the mt suffix, as per the usual Boost convention.
Boost also features the following new libraries:
• Foreach
• Statechart
• TR1
• Typeof
• Xpressive
• Asio
• Bitmap
• Circular Buffer
• Function Types
• Fusion
• GIL
• Interprocess
• Intrusive
• Math/Special Functions
• Math/Statistical Distributions
• MPI
• System
• Accumulators
• Exception
• Units
• Unordered
• Proto
• Flyweight
• Scope Exit
• Swap
• Signals2
• Property Tree
Many of the existing libraries have been improved, bug-fixed, and otherwise enhanced.

#### 4.3.3.2. Boost Documentation

The boost-doc package provides manuals and reference information in HTML form located in the following directory:
file:///usr/share/doc/boost-doc-version/index.html
The main site for the development of Boost is hosted on boost.org.

### 4.3.4. Qt

The qt package provides the Qt (pronounced "cute") cross-platform application development framework used in the development of GUI programs. Aside from being a popular "widget toolkit", Qt is also used for developing non-GUI programs such as console tools and servers. Qt was used in the development of notable projects such as Google Earth, KDE, Opera, OPIE, VoxOx, Skype, VLC media player and VirtualBox. It is produced by Nokia's Qt Development Frameworks division, which came into being after Nokia's acquisition of the Norwegian company Trolltech, the original producer of Qt, on June 17, 2008.
Qt uses standard C++ but makes extensive use of a special pre-processor called the Meta Object Compiler (MOC) to enrich the language. Qt can also be used in other programming languages via language bindings. It runs on all major platforms and has extensive internationalization support. Non-GUI Qt features include SQL database access, XML parsing, thread management, network support, and a unified cross-platform API for file handling.
Distributed under the terms of the GNU Lesser General Public License (among others), Qt is free and open source software. The Red Hat Enterprise Linux 6 version of Qt supports a wide range of compilers, including the GCC C++ compiler and the Visual Studio suite.

Some of the improvements the Red Hat Enterprise Linux 6 version of Qt include:
• Advanced Graphics Effects: options for opacity, drop-shadows, blur, colorization, and other similar effects
• Animation and State Machine: create simple or complex animations without the hassle of managing complex code
• Gesture and multi-touch support
• Support for new platforms
• Windows 7, Mac OSX 10.6, and other desktop platforms are now supported
• Added support for mobile development; Qt is optimized for the upcoming Maemo 6 platform, and will soon be ported to Maemo 5. In addition, Qt now supports the Symbian platform, with integration for the S60 framework.
• Added support for Real-Time Operating Systems such as QNX and VxWorks
• Improved performance, featuring added support for hardware-accelerated rendering (along with other rendering updates)
• Updated cross-platform IDE
For more details on updates to Qt included in Red Hat Enterprise Linux 6, refer to the following links:

#### 4.3.4.2. Qt Creator

Qt Creator is a cross-platform IDE tailored to the needs of Qt developers. It includes the following graphical tools:
• An advanced C++ code editor
• Integrated GUI layout and forms designer
• Project and build management tools
• Integrated, context-sensitive help system
• Visual debugger

#### 4.3.4.3. Qt Library Documentation

The qt-doc package provides HTML manuals and references located in /usr/share/doc/qt4/html/. This package also provides the Qt Reference Documentation, which is an excellent starting point for development within the Qt framework.
You can also install further demos and examples from qt-demos and qt-examples. To get an overview of the capabilities of the Qt framework, refer to /usr/bin/qtdemo-qt4 (provided by qt-demos).
For more information on the development of Qt, refer to the following online resources:

### 4.3.5. KDE Development Framework

The kdelibs-devel package provides the KDE libraries, which build on Qt to provide a framework for making application development easier. The KDE development framework also helps provide consistency across the KDE desktop environment.

#### 4.3.5.1. KDE4 Architecture

The KDE development framework's architecture in Red Hat Enterprise Linux 6 uses KDE4, which is built on the following technologies:
Plasma
Plasma replaces KDesktop in KDE4. Its implementation is based on the Qt Graphics View Framework, which was introduced in Qt 4.2. For more information about Plasma, refer to http://techbase.kde.org/Development/Architecture/KDE4/Plasma.
Sonnet
Sonnet is a multilingual spell-checking application that supports automatic language detection, primary/backup dictionaries, and other useful features. It replaces kspell2 in KDE4.
KIO
The KIO library provides a framework for network-transparent file handling, allowing users to easily access files through network-transparent protocols. It also helps provides standard file dialogs.
KJS/KHTML
KJS and KHTML are fully-fledged JavaScript and HTML engines used by different applications native to KDE4 (such as konqueror).
Solid
Solid is a hardware and network awareness framework that allows you to develop applications with hardware interaction features. Its comprehensive API provides the necessary abstraction to support cross-platform application development. For more information, refer to http://techbase.kde.org/Development/Architecture/KDE4/Solid.
Phonon
Phonon is a multimedia framework that helps you develop applications with multimedia functionalities. It facilitates the usage of media capabilities within KDE. For more information, refer to http://techbase.kde.org/Development/Architecture/KDE4/Phonon.
Telepathy
Telepathy provides a real-time communication and collaboration framework within KDE4. Its primary function is to tighten integration between different components within KDE. For a brief overview on the project, refer to http://community.kde.org/Real-Time_Communication_and_Collaboration.
KDE4 also features an easy-to-use Qt-based framework for adding online help capabilities to applications. Such capabilities include tooltips, hover-help information, and khelpcenter manuals. For a brief overview on online help within KDE4, refer to http://techbase.kde.org/Development/Architecture/KDE4/Providing_Online_Help.
KXMLGUI
KXMLGUI is a framework for designing user interfaces using XML. This framework allows you to design UI elements based on "actions" (defined by the developer) without having to revise source code. For more information, refer to http://developer.kde.org/documentation/library/kdeqt/kde3arch/xmlgui.html.
Strigi
Strigi is a desktop search daemon compatible with many desktop environments and operating systems. It uses its own jstream system which allows for deep indexing of files. For more information on the development of Strigi, refer to http://www.vandenoever.info/software/strigi/.
KNewStuff2
KNewStuff2 is a collaborative data sharing library used by many KDE4 applications. For more information, refer to http://techbase.kde.org/Projects/KNS2.

#### 4.3.5.2. kdelibs Documentation

The kdelibs-apidocs package provides HTML documentation for the KDE development framework in /usr/share/doc/HTML/en/kdelibs4-apidocs/. The following links also provide details on KDE-related programming tasks:

### 4.3.6. NSS Shared Databases

The NSS shared database format, introduced on NSS 3.12, is now available in Red Hat Enterprise 6. This encompasses a number of new features and components to improve access and usability.
Included, is the NSS certificate and key database which are now sqlite-based and allow for concurrent access. The legacy key3.db and cert8.db are also replaced with new SQL databases called key4.db and cert9.db. These new databases will store PKCS #11 token objects, which are the same as what is currently stored in cert8.db and key3.db.
Having support for shared databases enables a system-wide NSS database. It resides in /etc/pki/nssdb where globally trusted CA certificates become accessible to all applications. The command rv = NSS_InitReadWrite("sql:/etc/pki/nssdb"); initializes NSS for applications. If the application is run with root privileges, then the system-wide database is available on a read and write basis. However, if it is run with normal user privileges it becomes read only.
Additionally, a PEM PKCS #11 module for NSS allows applications to load into memory certificates and keys stored in PEM-formatted files (for example, those produced by openssl).

#### 4.3.6.1. Backwards Compatibility

The binary compatibility guarantees made by NSS upstream are preserved in NSS for Red Hat Enterprise Linux 6. This guarantee states that the NSS 3.12 is backwards compatible with all older NSS 3.x shared libraries. Therefore, a program linked with an older NSS 3.x shared library will work without recompiling or relinking, and any applications that restrict the use of NSS APIs to the NSS Public Functions remain compatible with future versions of the NSS shared libraries.
Red Hat Enterprise Linux 5 and 4 run on the same version of NSS as Red Hat Enterprise Linux 6 so there are no ABI or API changes. However, there are still differences as NSS's internal cryptographic module in Red Hat Enterprise Linux 6 is the one from NSS 3.12, whereas Red Hat Enterprise Linux 5 and 4 still use the older one from NSS 3.15. This means that new functionality that had been introduced with NSS 3.12, such as the shared database, is now available with Red Hat Enterprise Linux 6's version of NSS.

#### 4.3.6.2. NSS Shared Databases Documentation

Mozilla's wiki page explains the system-wide database rationale in great detail and can be accessed here.

### 4.3.7. Python

The python package adds support for the Python programming language. This package provides the object and cached bytecode files needed to enable runtime support for basic Python programs. It also contains the python interpreter and the pydoc documentation tool. The python-devel package contains the libraries and header files needed for developing Python extensions.
Red Hat Enterprise Linux also ships with numerous python-related packages. By convention, the names of these packages have a python prefix or suffix. Such packages are either library extensions or python bindings to an existing library. For instance, dbus-python is a Python language binding for D-Bus.
Note that both cached bytecode (*.pyc/*.pyo files) and compiled extension modules (*.so files) are incompatible between Python 2.4 (used in Red Hat Enterprise Linux 5) and Python 2.6 (used in Red Hat Enterprise Linux 6). As such, you will need to rebuild any extension modules you use that are not part of Red Hat Enterprise Linux.

The Red Hat Enterprise Linux 6 version of Python features various language changes. For information about these changes, refer to the following project resources:
Both resources also contain advice on porting code developed using previous Python versions.

#### 4.3.7.2. Python Documentation

For more information about Python, refer to man python. You can also install python-docs, which provides HTML manuals and references in the following location:
file:///usr/share/doc/python-docs-version/html/index.html
For details on library and language components, use pydoc component_name. For example, pydoc math will display the following information about the math Python module:
Help on module math:

NAME
math

FILE

DESCRIPTION
mathematical functions defined by the C standard.

FUNCTIONS
acos[...]
acos(x)

Return the arc cosine (measured in radians) of x.

acosh[...]
acosh(x)

Return the hyperbolic arc cosine (measured in radians) of x.

asin(...)
asin(x)

Return the arc sine (measured in radians) of x.

asinh[...]
asinh(x)

Return the hyperbolic arc sine (measured in radians) of x.

The main site for the Python development project is hosted on python.org.

### 4.3.8. Java

The java-1.6.0-openjdk package adds support for the Java programming language. This package provides the java interpreter. The java-1.6.0-openjdk-devel package contains the javac compiler, as well as the libraries and header files needed for developing Java extensions.
Red Hat Enterprise Linux also ships with numerous java-related packages. By convention, the names of these packages have a java prefix or suffix.

#### 4.3.8.1.  Java Documentation

For more information about Java, refer to man java. Some associated utilities also have their own respective man pages.
You can also install other Java documentation packages for more details about specific Java utilities. By convention, such documentation packages have the javadoc suffix (e.g. dbus-java-javadoc).
The main site for the development of Java is hosted on http://openjdk.java.net/. The main site for the library runtime of Java is hosted on http://icedtea.classpath.org.

### 4.3.9. Ruby

The ruby package provides the Ruby interpreter and adds support for the Ruby programming language. The ruby-devel package contains the libraries and header files needed for developing Ruby extensions.
Red Hat Enterprise Linux also ships with numerous ruby-related packages. By convention, the names of these packages have a ruby or rubygem prefix or suffix. Such packages are either library extensions or Ruby bindings to an existing library.
Examples of ruby-related packages include:
• ruby-flexmock
• rubygem-flexmock
• rubygems
• ruby-irb
• ruby-libguestfs
• ruby-libs
• ruby-qpid
• ruby-rdoc
• ruby-ri
• ruby-saslwrapper
• ruby-static
• ruby-tcltk
For information about updates to the Ruby language in Red Hat Enterprise Linux 6, refer to the following resources:
• file:///usr/share/doc/ruby-version/NEWS
• file:///usr/share/doc/ruby-version/NEWS-version

#### 4.3.9.1. Ruby Documentation

For more information about Ruby, refer to man ruby. You can also install ruby-docs, which provides HTML manuals and references in the following location:
file:///usr/share/doc/ruby-docs-version/
The main site for the development of Ruby is hosted on http://www.ruby-lang.org. The http://www.ruby-doc.org site also contains Ruby documentation.

### 4.3.10. Perl

The perl package adds support for the Perl programming language. This package provides Perl core modules, the Perl Language Interpreter, and the PerlDoc tool.
Red Hat also provides various perl modules in package form; these packages are named with the perl-* prefix. These modules provide stand-alone applications, language extensions, Perl libraries, and external library bindings.

Red Hat Enterprise Linux 6.0 ships with perl-5.10.1. If you are running an older system, rebuild or alter external modules and applications accordingly in order to ensure optimum performance.
For a full list of the differences between the Perl versions refer to the following documents:

#### 4.3.10.2. Installation

Perl's capabilities can be extended by installing additional modules. These modules come in the following forms:
Official Red Hat RPM
The official module packages can be installed with yum or rpm from the Red Hat Enterprise Linux repositories. They are installed to /usr/share/perl5 and either /usr/lib/perl5 for 32bit architectures or /usr/lib64/perl5 for 64bit architectures.
Modules from CPAN
Use the cpan tool provided by the perl-CPAN package to install modules directly from the CPAN website. They are installed to /usr/local/share/perl5 and either /usr/local/lib/perl5 for 32bit architectures or /usr/local/lib64/perl5 for 64bit architectures.
Third party module package
Third party modules are installed to /usr/share/perl5/vendor_perl and either /usr/lib/perl5/vendor_perl for 32bit architectures or /usr/lib64/perl5/vendor_perl for 64bit architectures.
Custom module package / manually installed module
These should be placed in the same directories as third party modules. That is, /usr/share/perl5/vendor_perl and either /usr/lib/perl5/vendor_perl for 32bit architectures or /usr/lib64/perl5/vendor_perl for 64bit architectures.

## Warning

If an official version of a module is already installed, installing its non-official version can create conflicts in the /usr/share/man directory.

#### 4.3.10.3. Perl Documentation

The perldoc tool provides documentation on language and core modules. To learn more about a module, use perldoc module_name. For example, perldoc CGI will display the following information about the CGI core module:
NAME
CGI - Handle Common Gateway Interface requests and responses

SYNOPSIS
use CGI;

my $q = CGI->new; [...] DESCRIPTION CGI.pm is a stable, complete and mature solution for processing and preparing HTTP requests and responses. Major features including processing form submissions, file uploads, reading and writing cookies, query string generation and manipulation, and processing and preparing HTTP headers. Some HTML generation utilities are included as well. [...] PROGRAMMING STYLE There are two styles of programming with CGI.pm, an object-oriented style and a function-oriented style. In the object-oriented style you create one or more CGI objects and then use object methods to create the various elements of the page. Each CGI object starts out with the list of named parameters that were passed to your CGI script by the server. [...]  For details on Perl functions, use perldoc -f function_name. For example, perldoc -f split wil display the following information about the split function: split /PATTERN/,EXPR,LIMIT split /PATTERN/,EXPR split /PATTERN/ split Splits the string EXPR into a list of strings and returns that list. By default, empty leading fields are preserved, and empty trailing ones are deleted. (If all fields are empty, they are considered to be trailing.) In scalar context, returns the number of fields found. In scalar and void context it splits into the @_ array. Use of split in scalar and void context is deprecated, however, because it clobbers your subroutine arguments. If EXPR is omitted, splits the$_ string.  If PATTERN is also omitted, splits on whitespace (after skipping any leading whitespace).  Anything matching PATTERN is taken to be a delimiter separating the fields.  (Note that the delimiter may be longer than one character.)

[...]

Current PerlDoc documentation can be found on perldoc.perl.org.
Core and external modules are documented on the Comprehensive Perl Archive Network.

[1] MPI support is not available on IBM System Z machines (where Open MPI is not available).

## Chapter 5.  Compiling and Building

Red Hat Enterprise Linux 6 includes many packages used for software development, including tools for compiling and building source code. This chapter discusses several of these packages and tools used to compile source code.

## 5.1. GNU Compiler Collection (GCC)

The GNU Compiler Collection (GCC) is a set of tools for compiling a variety of programming languages (including C, C++, ObjectiveC, ObjectiveC++, Fortran, and Ada) into highly optimized machine code. These tools include various compilers (like gcc and g++), run-time libraries (like libgcc, libstdc++, libgfortran, and libgomp), and miscellaneous other utilities.

### 5.1.1. GCC Status and Features

GCC for Red Hat Enterprise Linux 6 is based on the 4.4.x release series and includes several bug fixes, enhancements, and backports from upcoming releases (including the GCC 4.5). However, GCC 4.5 was not considered sufficiently mature for an enterprise distribution when RHEL6 features were frozen.
This standardization means that as updates to the 4.4 series become available (4.4.1, 4.4.2, ect), they will be incorporated into the compiler included with RHEL6 as updates. Red Hat may import additional backports and enhancements from upcoming releases outside the 4.4 series that won't break compatibility within the Enterprise Linux release. Occasionally, code that was not compliant to standards may fail to compile or its functionality may change in the process of fixing bugs or maintaining standards compliant behavior.
Since the previous release of Red Hat Enterprise Linux, GCC has had three major releases: 4.2.x, 4.3.x, and 4.4.x. A selective summary of the expansive list of changes follows.
• The inliner, dead code elimination routines, compile time, and memory usage codes are now improved. This release also features a new register allocator, instruction scheduler, and software pipeliner.
• Version 3.0 of the OpenMP specification is now supported for the C, C++, and Fortran compilers.
• Experimental support for the upcoming ISO C++ standard (C++0x) is included. This has support for auto/inline namespaces, character types, and scoped enumerations. To enable this, use the compiler options -std=c++0x (which disables GNU extensions) or -std=gnu++0x.
For a more detailed list of the status of C++0x improvements, refer to:
• GCC now incorporates the Variable Tracking at Assignments (VTA) infrastructure. This allows GCC to better track variables during optimizations so that it can produce improved debugging information (i.e. DWARF) for the GNU Project Debugger, SystemTap, and other tools. For a brief overview of VTA, refer to Section 6.3, “Variable Tracking at Assignments”.
With VTA you can debug optimized code drastically better than with previous GCC releases, and you do not have to compile with -O0 to provide a better debugging experience.
• Fortran 2008 is now supported, while support for Fortran 2003 is extended.
For a more detailed list of improvements in GCC, refer to:
In addition to the changes introduced via the GCC 4.4 rebase, the Red Hat Enterprise Linux 6 version of GCC also features several fixes and enhancements backported from upstream sources (i.e. version 4.5 and beyond). These improvements include the following (among others):
• Improved DWARF3 debugging for debugging optimized C++ code.
• Fortran optimization improvements.
• More accurate instruction length information for ix86, Intel 64 and AMD64, and s390.
• Intel Atom support
• POWER7 support
• C++ raw string support, u/U/u8 string literal support

### 5.1.2. Language Compatibility

Application Binary Interfaces specified by the GNU C, C++, Fortran and Java Compiler include:
• Calling conventions. These specify how arguments are passed to functions and how results are returned from functions.
• Register usage conventions. These specify how processor registers are allocated and used.
• Object file formats. These specify the representation of binary object code.
• Size, layout, and alignment of data types. These specify how data is laid out in memory.
• Interfaces provided by the runtime environment. Where the documented semantics do not change from one version to another they must be kept available and use the same name at all times.
The default system C compiler included with Red Hat Enterprise Linux 6 is largely compatible with the C99 ABI standard. Deviations from the C99 standard in GCC 4.4 are tracked online.
In addition to the C ABI, the Application Binary Interface for the GNU C++ Compiler specifies the binary interfaces needed to support the C++ language, such as:
• Name mangling and demangling
• Creation and propagation of exceptions
• Formatting of run-time type information
• Constructors and destructors
• Layout, alignment, and padding of classes and derived classes
• Virtual function implementation details, such as the layout and alignment of virtual tables
The default system C++ compiler included with Red Hat Enterprise Linux 6 conforms to the C++ ABI defined by the Itanium C++ ABI (1.86).
Although every effort has been made to keep each version of GCC compatible with previous releases, some incompatibilities do exist.
##### ABI incompatibilities between RHEL6 and RHEL5
The following is a list of known incompatibilities between the Red Hat Enterprise Linux 6 and 5 toolchains.
• Passing/returning structs with flexible array members by value changed in some cases on Intel 64 and AMD64.
• Passing/returning of unions with long double members by value changed in some cases on Intel 64 and AMD64.
• Passing/returning structs with complex float member by value changed in some cases on Intel 64 and AMD64.
• Passing of 256-bit vectors on x86, Intel 64 and AMD64 platforms changed when -mavx is used.
• There have been multiple changes in passing of _Decimal{32,64,128} types and aggregates containing those by value on several targets.
• Packing of packed char bitfields changed in some cases.
##### ABI incompatibilities between RHEL5 and RHEL4
The following is a list of known incompatibilities between the Red Hat Enterprise Linux 5 and 4 toolchains.
• There have been changes in the library interface specified by the C++ ABI for thread-safe initialization of function-scope static variables.
• On Intel 64 and AMD64, the medium model for building applications where data segment exceeds 4GB, was redesigned to match the latest ABI draft at the time. The ABI change results in incompatibility among medium model objects.
The compiler flag -Wabi can be used to get diagnostics indicating where these constructs appear in source code, though it will not catch every single case. This flag is especially useful for C++ code to warn whenever the compiler generates code that is known to be incompatible with the vendor-neutral C++ ABI.
Excluding the incompatibilities listed above, the GCC C and C++ language ABIs are mostly ABI compatible. The vast majority of source code will not encounter any of the known issues, and can be considered compatible.
Compatible ABIs allow the objects created by compiling source code to be portable to other systems. In particular, for Red Hat Enterprise Linux, this allows for upward compatibility. Upward compatibility is defined as the ability to link shared libraries and objects, created using a version of the compilers in a particular RHEL release, with no problems. This includes new objects compiled on subsequent RHEL releases.
The C ABI is considered to be stable, and has been so since at least RHEL3 (again, barring any incompatibilities mentioned in the above lists). Libraries built on RHEL3 and later can be linked to objects created on a subsequent environment (RHEL4, RHEL5, and RHEL6).
The C++ ABI is considered to be stable, but less stable than the C ABI, and only as of RHEL4 (corresponding to GCC version 3.4 and above.). As with C, this is only an upward compatibility. Libraries built on RHEL4 and above can be linked to objects created on a subsequent environment (RHEL5, and RHEL6).
To force GCC to generate code compatible with the C++ ABI in RHEL releases prior to RHEL4, some developers have used the -fabi-version=1 option. This practice is not recommended. Objects created this way are indistinguishable from objects conforming to the current stable ABI, and can be linked (incorrectly) amongst the different ABIs, especially when using new compilers to generate code to be linked with old libraries that were built with tools prior to RHEL4.

## Warning

The above incompatibilities make it incredibly difficult to maintain ABI shared library sanity between releases, especially when developing custom libraries with multiple dependencies outside of the core libraries. Therefore, if shared libraries are developed, it is highly recommend that a new version is built for each Red Hat Enterprise Linux release.

### 5.1.3. Object Compatibility and Interoperability

Two items that are important are the changes and enhancements in the underlying tools used by the compiler, and the compatibility between the different versions of a language's compiler.
Changes and new features in tools like ld (distributed as part of the binutils package) or in the dynamic loader (ld.so, distributed as part of the glibc package) can subtly change the object files that the compiler produces. These changes mean that object files moving to the current release of Red Hat Enterprise Linux from previous releases may loose functionality, behave differently at runtime, or otherwise interoperate in a diminished capacity. Known problem areas include:
• ld --build-id
In RHEL6 this is passed to ld by default, whereas RHEL5 ld doesn't recognize it.
• as .cfi_sections support
In RHEL6 this directive allows .debug_frame, .eh_frame or both to be emitted from .cfi* directives. In RHEL5 only .eh_frame is emitted.
• as, ld, ld.so, and gdb STB_GNU_UNIQUE and %gnu_unique_symbol support
In RHEL6 more debug information is generated and stored in object files. This information relies on new features detailed in the DWARF standard, and also on new extensions not yet standardized. In RHEL5, tools like as, ld, gdb, objdump, and readelf may not be prepared for this new information and may fail to interoperate with objects created with the newer tools. In addition, RHEL5 produced object files do not support these new features; these object files may be handled by RHEL6 tools in a sub-optimal manner.
An outgrowth of this enhanced debug information is that the debuginfo packages that ship with system libraries allow you to do useful source level debugging into system libraries if they are installed. Refer to Section 6.1, “Installing Debuginfo Packages” for more information on debuginfo packages.
Object file changes, such as the ones listed above, may interfere with the portable use of prelink.

### 5.1.4. Backwards Compatibility Packages

Several packages are provided to serve as an aid for those moving source code or executables from older versions of Red Hat Enterprise Linux to the current release. These packages are intended to be used as a temporary aid in transitioning sources to newer compilers with changed behavior, or as a convenient way to otherwise isolate differences in the system environment from the compile environment.

## Note

Please be advised that Red Hat may remove these packages in future Red Hat Enterprise Linux releases.
The following packages provide compatibility tools for compiling Fortran or C++ source code on the current release of Red Hat Enterprise Linux 6 as if one was using the older compilers on Red Hat Enterprise Linux 4:
• compat-gcc-34
• compat-gcc-34-c++
• compat-gcc-34-g77
The following package provides a compatibility runtime library for Fortran executables compiled on Red Hat Enterprise Linux 5 to run without recompilation on the current release of Red Hat Enterprise Linux 6:
• compat-libgfortran-41
Please note that backwards compatibility library packages are not provided for all supported system libraries, just the system libraries pertaining to the compiler and the C/C++ standard libraries.
For more information about backwards compatibility library packages, refer to the Application Compatibility section of the Red Hat Enterprise Linux 6 Migration Guide.

### 5.1.5. Previewing RHEL6 compiler features on RHEL5

On Red Hat Enterprise Linux 5, we have included the package gcc44 as an update. This is a backport of the RHEL6 compiler to allow users running RHEL5 to compile their code with the RHEL6 compiler and experiment with new features and optimizations before upgrading their systems to the next major release. The resulting binary will be forward compatible with RHEL6, so one can compile on RHEL5 with gcc44 and run on RHEL5, RHEL6, and above.
The RHEL5 gcc44 compiler will be kept reasonably in step with the GCC 4.4.x that we ship with RHEL6 to ease transition. Though, to get the latest features, it is recommended RHEL6 is used for development. The gcc44 is only provided as an aid in the conversion process.

### 5.1.6. Running GCC

To compile using GCC tools, first install binutils and gcc; doing so will also install several dependencies.
In brief, the tools work via the gcc command. This is the main driver for the compiler. It can be used from the command line to pre-process or compile a source file, link object files and libraries, or perform a combination thereof. By default, gcc takes care of the details and links in the provided libgcc library.
The compiler functions provided by GCC are also integrated into the Eclipse IDE as part of the CDT. This presents many advantages, particularly for developers who prefer a graphical interface and fully integrated environment. For more information about compiling in Eclipse, refer to Section 1.3, “ Development Toolkits”.
Conversely, using GCC tools from the command-line interface consumes less system resources. This also allows finer-grained control over compilers; GCC's command-line tools can even be used outside of the graphical mode (runlevel 5).

#### 5.1.6.1. Simple C Usage

Basic compilation of a C language program using GCC is easy. Start with the following simple program:
##### hello.c
#include <stdio.h>

int main ()
{
printf ("Hello world!\n");
return 0;
}

The following procedure illustrates the compilation process for C in its most basic form.
###### Procedure 5.1. Compiling a 'Hello World' C Program
1. Compile hello.c into an executable with:
gcc hello.c -o hello
Ensure that the resulting binary hello is in the same directory as hello.c.
2. Run the hello binary, i.e. hello.

#### 5.1.6.2. Simple C++ Usage

Basic compilation of a C++ language program using GCC is similar. Start with the following simple program:
##### hello.cc
#include <iostream>

using namespace std;

int main(void)
{
cout << "Hello World!" << endl;
return 0;
}

The following procedure illustrates the compilation process for C++ in its most basic form.
###### Procedure 5.2. Compiling a 'Hello World' C++ Program
1. Compile hello.cc into an executable with:
g++ hello.cc -o hello
Ensure that the resulting binary hello is in the same directory as hello.cc.
2. Run the hello binary, i.e. hello.

#### 5.1.6.3. Simple Multi-File Usage

To use basic compilation involving multiple files or object files, start with the following two source files:
##### one.c
#include <stdio.h>
void hello()
{
printf("Hello world!\n");
}

##### two.c
extern void hello();

int main()
{
hello();
return 0;
}

The following procedure illustrates a simple, multi-file compilation process in its most basic form.
###### Procedure 5.3. Compiling a Program with Multiple Source Files
1. Compile one.c into an executable with:
gcc -c one.c -o one.o
Ensure that the resulting binary one.o is in the same directory as one.c.
2. Compile two.c into an executable with:
gcc -c two.c -o two.o
Ensure that the resulting binary two.o is in the same directory as two.c.
3. Compile the two object files one.o and two.o into a single executable with:
gcc one.o two.o -o hello
Ensure that the resulting binary hello is in the same directory as one.o and two.o.
4. Run the hello binary, i.e. hello.

#### 5.1.6.4. Recommended Optimization Options

Different projects require different optimization options. There is no one-size-fits-all approach when it comes to optimization, but here are a few guidelines to keep in mind.
##### Instruction selection and tuning
It is very important to chose the correct architecture for instruction scheduling. By default GCC produces code is optimized for the most common processors, but if the CPU on which your code will run is known, the corresponding -mtune= option to optimize the instruction scheduling, and -march= option to optimize the instruction selection should be used.
The option -mtune= optimizes instruction scheduling to fit your architecture by tuning everything except the ABI and the available instruction set. This option will not chose particular instructions, but instead will tune your program in such a way that executing on a particular architecture will be optimized. For example, if an Intel Core2 CPU will predominantly be used, choose -mtune=core2. If the wrong choice is made, the program will still run, but not optimally on the given architecture. The architecture on which the program will most likely run should always be chosen.
The option -march= optimizes instruction selection. As such, it is important to choose correctly as choosing incorrectly will cause your program to fail. This option selects the instruction set used when generating code. For example, if the program will be run on an AMD K8 core based CPU, choose -march=k8. Specifying the architecture with this option will imply -mtune=.
The -mtune= and -march= commands should only be used for tuning and selecting instructions within a given architecture, not to generate code for a different architecture (also known as cross-compiling). For example, this is not to be used to generate PowerPC code from an Intel 64 and AMD64 platform.
For a complete list of the available options for both -march= and -mtune=, refer to the GCC documentation available here: GCC 4.4.4 Manual: Hardware Models and Configurations
##### General purpose optimization flags
The compiler flag -O2 is a good middle of the road option to generate fast code. It produces the best optimized code when the resulting code size is not large. Use this when unsure what would best suit.
When code size is not an issue, -O3 is preferable. This option produces code that is slightly larger but runs faster because of a more frequent inline of functions. This is ideal for floating point intensive code.
The other general purpose optimization flag is -Os. This flag also optimizes for size, and produces faster code in situations where a smaller footprint will increase code locality, thereby reducing cache misses.
Use -frecord-gcc-switches when compiling objects. This records the options used to build objects into objects themselves. After an object is built, it determines which set of options were used to build it. The set of options are then recorded in a section called .GCC.command.line within the object and can be examined with the following:
$gcc -frecord-gcc-switches -O3 -Wall hello.c -o hello$ readelf --string-dump=.GCC.command.line hello

String dump of section '.GCC.command.line':
[     0]  hello.c
[     8]  -mtune=generic
[    17]  -O3
[    1b]  -Wall
[    21]  -frecord-gcc-switches

It is very important to test and try different options with a representative data set. Often, different modules or objects can be compiled with different optimization flags in order to produce optimal results. Refer to Section 5.1.6.5, “Using Profile Feedback to Tune Optimization Heuristics.” for additional optimization tuning.

#### 5.1.6.5. Using Profile Feedback to Tune Optimization Heuristics.

During the transformation of a typical set of source code into an executable, tens of hundreds of choices must be made about the importance of speed in one part of code over another, or code size as opposed to code speed. By default, these choices are made by the compiler using reasonable heuristics, tuned over time to produce the optimum runtime performance. However, GCC also has a way to teach the compiler to optimize executables for a specific machine in a specific production environment. This feature is called profile feedback.
Profile feedback is used to tune optimizations such as:
• Inlining
• Branch prediction
• Instruction scheduling
• Inter-procedural constant propagation
• determining of hot or cold functions
Profile feedback compiles a program first to generate a program that is run and analyzed and then a second time to optimize with the gathered data.
###### Procedure 5.4. Using Profile Feedback
1. Step One

The application must be instrumented to produce profiling information by compiling it with -fprofile-generate.
2. Step Two

Run the application to accumulate and save the profiling information.
3. Step Three

Recompile the application with -fprofile-use.
Step three will use the profile information gathered in step one to tune the compiler's heuristics while optimizing the code into a final executable.
###### Procedure 5.5. Compiling a Program with Profiling Feedback
1. Compile source.c to include profiling instrumentation:
gcc source.c -fprofile-generate -O2 -o executable
2. Run executable to gather profiling information:
./executable
3. Recompile and optimize source.c with profiling information gathered in step one:
gcc source.c -fprofile-use -O2 -o executable
Multiple data collection runs, as seen in step two, will accumulate data into the profiling file instead of replacing it. This allows the executable in step two to be run multiple times with additional representative data in order to collect even more information.
The executable must run with representative levels of both the machine being used and a respective data set large enough for the input needed. This ensures optimal results are achieved.
By default, GCC will generate the profile data into the directory where step one was performed. To generate this information elsewhere, compile with -fprofile-dir=DIR where DIR is the preferred output directory.

## Warning

The format of the compiler feedback data file changes between compiler versions. It is imperative that the program compilation is repeated with each version of the compiler.

#### 5.1.6.6. Using 32-bit compilers on a 64-bit host

On a 64-bit host, GCC will build executables that can only run on 64-bit hosts. However, GCC can be used to build executables that will run both on 64-bit hosts and on 32-bit hosts.
To build 32-bit binaries on a 64-bit host, first install 32-bit versions of any supporting libraries the executable may need. This must at least include supporting libraries for glibc and libgcc, and possibly for libstdc++ if the program is a C++ program. On Intel 64 and AMD64, this can be done with:
yum install glibc-devel.i686 libgcc.i686 libstdc++-devel.i686
There may be cases where it is useful to to install additional 32-bit libraries that a program may need. For example, if a program uses the db4-devel libraries to build, the 32-bit version of these libraries can be installed with:
yum install db4-devel.i686

## Note

The .i686 suffix on the x86 platform (as opposed to x86-64) specifies a 32-bit version of the given package. For PowerPC architectures, the suffix is ppc (as opposed to ppc64).
After the 32-bit libraries have been installed, the -m32 option can be passed to the compiler and linker to produce 32-bit executables. Provided the supporting 32-bit libraries are installed on the 64-bit system, this executable will be able to run on both 32-bit systems and 64-bit systems.
###### Procedure 5.6. Compiling a 32-bit Program on a 64-bit Host
1. On a 64-bit system, compile hello.c into a 64-bit executable with:
gcc hello.c -o hello64
2. Ensure that the resulting executable is a 64-bit binary:
$file hello64 hello64: ELF 64-bit LSB executable, x86-64, version 1 (GNU/Linux), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, not stripped$ ldd hello64
linux-vdso.so.1 =>  (0x00007fff242dd000)
libc.so.6 => /lib64/libc.so.6 (0x00007f0721514000)
/lib64/ld-linux-x86-64.so.2 (0x00007f0721893000)

The command file on a 64-bit executable will include ELF 64-bit in its output, and ldd will list /lib64/libc.so.6 as the main C library linked.
3. On a 64-bit system, compile hello.c into a 32-bit executable with:
gcc -m32 hello.c -o hello32
4. Ensure that the resulting executable is a 32-bit binary:
$file hello32 hello32: ELF 32-bit LSB executable, Intel 80386, version 1 (GNU/Linux), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, not stripped$ ldd hello32
linux-gate.so.1 =>  (0x007eb000)
libc.so.6 => /lib/libc.so.6 (0x00b13000)
/lib/ld-linux.so.2 (0x00cd7000)

The command file on a 32-bit executable will include ELF 32-bit in its output, and ldd will list /lib/libc.so.6 as the main C library linked.
If you have not installed the 32-bit supporting libraries you will get an error similar to this for C code:
$gcc -m32 hello32.c -o hello32 /usr/bin/ld: crt1.o: No such file: No such file or directory collect2: ld returned 1 exit status  A similar error would be triggered on C++ code: $ g++ -m32 hello32.cc -o hello32-c++
In file included from /usr/include/features.h:385,
from /usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../include/c++/4.4.4/x86_64-redhat-linux/32/bits/os_defines.h:39,
from /usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../include/c++/4.4.4/x86_64-redhat-linux/32/bits/c++config.h:243,
from /usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../include/c++/4.4.4/iostream:39,
from hello32.cc:1:
/usr/include/gnu/stubs.h:7:27: error: gnu/stubs-32.h: No such file or directory

These errors indicate that the supporting 32-bit libraries have not been properly installed as explained at the beginning of this section.
Also important is to note that building with -m32 will in not adapt or convert a program to resolve any issues arising from 32/64-bit incompatibilities. For tips on writing portable code and converting from 32-bits to 64-bits, see the paper entitled Porting to 64-bit GNU/Linux Systems in the Proceedings of the 2003 GCC Developers Summit.

### 5.1.7. GCC Documentation

For more information about GCC compilers, refer to the man pages for cpp, gcc, g++, gcj, and gfortran.
the following online user manuals are also available:
The main site for the development of GCC is gcc.gnu.org.

## 5.2. Distributed Compiling

Red Hat Enterprise Linux 6 also supports distributed compiling. This involves transforming one compile job into many smaller jobs; these jobs are distributed over a cluster of machines, which speeds up build time (particularly for programs with large codebases). The distcc package provides this capability.
To set up distributed compiling, install the following packages:
• distcc
• distcc-server
For more information about distributed compiling, refer to the man pages for distcc and distccd. The following link also provides detailed information about the development of distcc:

## 5.3. Autotools

GNU Autotools is a suite of command-line tools that allow developers to build applications on different systems, regardless of the installed packages or even Linux distribution. These tools aid developers in creating a configure script. This script runs prior to builds and creates the top-level Makefiles needed to build the application. The configure script may perform tests on the current system, create additional files, or run other directives as per parameters provided by the builder.
The Autotools suite's most commonly-used tools are:
autoconf
Generates the configure script from an input file (e.g. configure.ac)
automake
Creates the Makefile for a project on a specific system
autoscan
Generates a preliminary input file (i.e. configure.scan), which can be edited to create a final configure.ac to be used by autoconf
All tools in the Autotools suite are part of the Development Tools group package. You can install this package group to install the entire Autotools suite, or simply use yum to install any tools in the suite as you wish.

### 5.3.1. Autotools Plug-in for Eclipse

The Autotools suite is also integrated into the Eclipse IDE via the Autotools plug-in. This plug-in provides an Eclipse graphical user interface for Autotools, which is suitable for most C/C++ projects.
As of Red Hat Enterprise Linux 6, this plug-in only supports two templates for new C/C++ projects:
• An empty project
• A "hello world" application
The empty project template is used when importing projects into the C/C++ Development Toolkit that already support Autotools. Future updates to the Autotools plug-in will include additional graphical user interfaces (e.g. wizards) for creating shared libraries and other complex scenarios.
The Red Hat Enterprise Linux 6 version of the Autotools plug-in also does not integrate git or mercurial into Eclipse. As such, Autotools projects that use git repositories will need to be checked out outside the Eclipse workspace. Afterwards, you can specify the source location for such projects in Eclipse. Any repository manipulation (e.g. commits, updates) will need to be done via the command line.

### 5.3.2. Configuration Script

The most crucial function of Autotools is the creation of the configure script. This script tests systems for tools, input files, and other features it can use in order to build the project [2]. The configure script generates a Makefile which allows the make tool to build the project based on the system configuration.
To create the configure script, first create an input file. Then feed it to an Autotools utility in order to create the configure script. This input file is typically configure.ac or Makefile.am; the former is usually processed by autoconf, while the latter is fed to automake.
If a Makefile.am input file is available, the automake utility creates a Makefile template (i.e. Makefile. in), which may refer to information collected at configuration time. For example, the Makefile may need to link to a particular library if and only if that library is already installed. When the configure script runs, automake will use the Makefile. in templates to create a Makefile.
If a configure.ac file is available instead, then autoconf will automatically create the configure script based on the macros invoked by configure.ac. To create a preliminary configure.ac, use the autoscan utility and edit the file accordingly.

### 5.3.3. Autotools Documentation

Red Hat Enterprise Linux 6 includes man pages for autoconf, automake, autoscan and most tools included in the Autotools suite. In addition, the Autotools community provides extensive documentation on autoconf and automake on the following websites:
The following is an online book describing the use of Autotools. Although the above online documentation is the recommended and most up to date information on Autotools, this book is a good alternative and introduction.
For information on how to create Autotools input files, refer to:
The following upstream example also illustrates the use of Autotools in a simple hello program:
The Autotools Plug-in For Eclipse whitepaper also provides more detail on the Red Hat Enterprise Linux 6 release of the Autotools plug-in. This whitepaper also includes a "by example" case study to walk you through a typical use-case for the plug-in. Refer to the following link for more information:

## 5.4. Eclipse Built-in Specfile Editor

The Specfile Editor Plug-in for Eclipse provides useful features to help developers manage .spec files. This plug-in allows users to leverage several Eclipse GUI features in editing .spec files, such as auto-completion, highlighting, file hyperlinks, and folding.
In addition, the Specfile Editor Plug-in also integrates the rpmlint tool into the Eclipse interface. rpmlint is a command-line tool that helps developers detect common RPM package errors. The richer visualization offered by the Eclipse interface helps developers quickly detect, view, and correct mistakes reported by rpmlint.
The Specfile Editor for Eclipse is provided by the eclipse-rpm-editor package. For more information about this plug-in, refer to Specfile Editor User Guide in the Eclipse Help Contents.

[2] For information about tests that configure can perform, refer to the following link:

## Chapter 6. Debugging

Useful, well-written software generally goes through several different phases of application development, allowing ample opportunity for mistakes to be made. Some phases come with their own set of mechanisms to detect errors. For example, during compilation an elementary semantic analysis is often performed to make sure objects, such as variables and functions, are adequately described.
The error-checking mechanisms performed during each application development phase aims to catch simple and obvious mistakes in code. The debugging phase helps to bring more subtle errors to light that fell through the cracks during routine code inspection.

## 6.1. Installing Debuginfo Packages

Red Hat Enterprise Linux also provides -debuginfo packages for all architecture-dependent RPMs included in the operating system. A -debuginfo package contains accurate debugging information for its corresponding package. For Red Hat Enterprise Linux 6, the debuginfo packages are now available on a new channel on the Red Hat Network. To install the -debuginfo package of a package (i.e. typically packagename-debuginfo), first the machine needs to be subscribed to the corresponding Debuginfo channel. For example, for Red Hat Enterprise Server 6, the corresponding channel would be Red Hat Enterprise Linux Server Debuginfo (v. 6). Then use the following command:
debuginfo-install packagename

## Note

Attempting to debug a package without having its -debuginfo equivalent installed may fail, although GDB will try to provide any helpful diagnostics it can.

## 6.2. GDB

Fundamentally, like most debuggers, GDB manages the execution of compiled code in a very closely controlled environment. This environment makes possible the following fundamental mechanisms necessary to the operation of GDB:
• Inspect and modify memory within the code being debugged (e.g. reading and setting variables).
• Control the execution state of the code being debugged, principally whether it's running or stopped.
• Detect the execution of particular sections of code (e.g. stop running code when it reaches a specified area of interest to the programmer).
• Detect access to particular areas of memory (e.g. stop running code when it accesses a specified variable).
• Execute portions of code (from an otherwise stopped program) in a controlled manner.
• Detect various programmatic asynchronous events such as signals.
The operation of these mechanisms rely mostly on information produced by a compiler. For example, to view the value of a variable, GDB has to know:
• The location of the variable in memory
• The nature of the variable
This means that displaying a double-precision floating point value requires a very different process from displaying a string of characters. For something complex like a structure, GDB has to know not only the characteristics of each individual elements in the structure, but the morphology of the structure as well.
GDB requires the following items in order to fully function:
Debug Information
Much of GDB's operations rely on a program's debug information. While this information generally comes from compilers, much of it is necessary only while debugging a program, i.e. it is not used during the program's normal execution. For this reason, compilers do not always make that information available by default — GCC, for instance, must be explicitly instructed to provide this debugging information with the -g flag.
To make full use of GDB's capabilities, it is highly advisable to make the debug information available first to GDB. GDB can only be of very limited use when run against code with no available debug information.
Source Code
One of the most useful features of GDB (or any other debugger) is the ability to associate events and circumstances in program execution with their corresponding location in source code. This location normally refers to a specific line or series of lines in a source file. This, of course, would require that a program's source code be available to GDB at debug time.

### 6.2.1. Simple GDB

GDB literally contains dozens of commands. This section describes the most fundamental ones.
br (breakpoint)
The breakpoint command instructs GDB to halt execution upon reaching a specified point in the execution. That point can be specified a number of ways, but the most common are just as the line number in the source file, or the name of a function. Any number of breakpoints can be in effect simultaneously. This is frequently the first command issued after starting GDB.
r (run)
The run command starts the execution of the program. If run is executed with any arguments, those arguments are passed on to the executable as if the program has been started normally. Users normally issue this command after setting breakpoints.
Before an executable is started, or once the executable stops at, for example, a breakpoint, the state of many aspects of the program can be inspected. The following commands are a few of the more common ways things can be examined.
p (print)
The print command displays the value of the argument given, and that argument can be almost anything relevant to the program. Usually, the argument is simply the name of a variable of any complexity, from a simple single value to a structure. An argument can also be an expression valid in the current language, including the use of program variables and library functions, or functions defined in the program being tested.
bt (backtrace)
The backtrace displays the chain of function calls used up until the execution was terminated. This is useful for investigating serious bugs (such as segmentation faults) with elusive causes.
l (list)
When execution is stopped, the list command shows the line in the source code corresponding to where the program stopped.
The execution of a stopped program can be resumed in a number of ways. The following are the most common.
c (continue)
The continue command simply restarts the execution of the program, which will continue to execute until it encounters a breakpoint, runs into a specified or emergent condition (e.g. an error), or terminates.
n (next)
Like continue, the next command also restarts execution; however, in addition to the stopping conditions implicit in the continue command, next will also halt execution at the next sequential line of code in the current source file.
s (step)
Like next, the step command also halts execution at each sequential line of code in the current source file. However, if execution is currently stopped at a source line containing a function call, GDB stops execution after entering the function call (rather than executing it).
fini (finish)
Like the aforementioned commands, the finish command resumes executions, but halts when execution returns from a function.
Finally, two essential commands:
q (quit)
This terminates the execution.
h (help)
The help command provides access to its extensive internal documentation. The command takes arguments: help breakpoint (or h br), for example, shows a detailed description of the breakpoint command. Refer to the help output of each command for more detailed information.

### 6.2.2. Running GDB

This section will describe a basic execution of GDB, using the following simple program:
##### hello.c
#include <stdio.h>

char hello[] = { "Hello, World!" };

int
main()
{
fprintf (stdout, "%s\n", hello);
return (0);
}

The following procedure illustrates the debugging process in its most basic form.
###### Procedure 6.1. Debugging a 'Hello World' Program
1. Compile hello.c into an executable with the debug flag set, as in:
gcc -g -o hello hello.c
Ensure that the resulting binary hello is in the same directory as hello.c.
2. Run gdb on the hello binary, i.e. gdb hello.
3. After several introductory comments, gdb will display the default GDB prompt:
(gdb)
4. Some things can be done even before execution is started. The variable hello is global, so it can be seen even before the main procedure starts:
gdb) p hello
$1 = "Hello, World!" (gdb) p hello[0]$2 = 72 'H'
(gdb) p *hello
$3 = 72 'H' (gdb)  Note that the print targets hello[0] and *hello require the evaluation of an expression, as does, for example, *(hello + 1): (gdb) p *(hello + 1)$4 = 101 'e'

5. Next, list the source:
(gdb) l
1       #include <stdio.h>
2
3       char hello[] = { "Hello, World!" };
4
5       int
6       main()
7       {
8         fprintf (stdout, "%s\n", hello);
9         return (0);
10      }

The list reveals that the fprintf call is on line 8. Apply a breakpoint on that line and resume the code:
(gdb) br 8
Breakpoint 1 at 0x80483ed: file hello.c, line 8.
(gdb) r
Starting program: /home/moller/tinkering/gdb-manual/hello

Breakpoint 1, main () at hello.c:8
8         fprintf (stdout, "%s\n", hello);

6. Finally, use the next command to step past the fprintf call, executing it:
(gdb) n
Hello, World!
9         return (0);

The following sections describe more complex applications of GDB.

### 6.2.3. Conditional Breakpoints

In many real-world cases, a program may perform its task well during the first few thousand times; it may then start crashing or encountering errors during its eight thousandth iteration of the task. Debugging programs like this can be difficult, as it is hard to imagine a programmer with the patience to issue a continue command thousands of times just to get to the iteration that crashed.
Situations like this are common in real life, which is why GDB allows programmers to attach conditions to a breakpoint. For example, consider the following program:
##### simple.c
#include <stdio.h>

main()
{
int i;

for (i = 0;; i++) {
fprintf (stdout, "i = %d\n", i);
}
}

To set a conditional breakpoint at the GDB prompt:
(gdb) br 8 if i == 8936
Breakpoint 1 at 0x80483f5: file iterations.c, line 8.
(gdb) r

With this condition, the program execution will eventually stop with the following output:
i = 8931
i = 8932
i = 8933
i = 8934
i = 8935

Breakpoint 1, main () at iterations.c:8
8           fprintf (stdout, "i = %d\n", i);

Inspect the breakpoint information (using info br) to review the breakpoint status:
(gdb) info br
Num     Type           Disp Enb Address    What
1       breakpoint     keep y   0x080483f5 in main at iterations.c:8
stop only if i == 8936


### 6.2.4. Forked Execution

Among the more challenging bugs confronting programmers is where one program (the parent) makes an independent copy of itself (a fork). That fork then creates a child process which, in turn, fails. Debugging the parent process may or may not be useful. Often the only way to get to the bug may be by debugging the child process, but this is not always possible.
The set follow-fork-mode feature is used to overcome this barrier allowing programmers to follow a a child process instead of the parent process.
set follow-fork-mode parent
The original process is debugged after a fork. The child process runs unimpeded. This is the default.
set follow-fork-mode child
The new process is debugged after a fork. The parent process runs unimpeded.
show follow-fork-mode
Display the current debugger response to a fork call.
Use the set detach-on-fork command to debug both the parent and the child processes after a fork, or retain debugger control over them both.
set detach-on-fork on
The child process (or parent process, depending on the value of follow-fork-mode will be detached and allowed to run independently. This is the default.
set detach-on-fork off
Both processes will be held under the control of GDB. One process (child or parent, depending on the value of follow-fork-mode) is debugged as usual, while the other is suspended.
show detach-on-fork
Show whether detach-on-fork mode is on or off.
Consider the following program:
##### fork.c
#include <unistd.h>

int main()
{
pid_t  pid;
const char *name;

pid = fork();
if (pid == 0)
{
name = "I am the child";
}
else
{
name = "I am the parent";
}
return 0;
}

This program, compiled with the command gcc -g fork.c -o fork -lpthread and examined under GDB will show:
gdb ./fork
[...]
(gdb) break main
Breakpoint 1 at 0x4005dc: file fork.c, line 8.
(gdb) run
[...]
Breakpoint 1, main () at fork.c:8
8   pid = fork();
(gdb) next
Detaching after fork from child process 3840.
9   if (pid == 0)
(gdb) next
15       name = "I am the parent";
(gdb) next
17   return 0;
(gdb) print name
$1 = 0x400717 "I am the parent" GDB followed the parent process and allowed the child process (process 3840) to continue execution. The following is the same test using set follow-fork-mode child. (gdb) set follow-fork-mode child (gdb) break main Breakpoint 1 at 0x4005dc: file fork.c, line 8. (gdb) run [...] Breakpoint 1, main () at fork.c:8 8 pid = fork(); (gdb) next [New process 3875] [Thread debugging using libthread_db enabled] [Switching to Thread 0x7ffff7fd5720 (LWP 3875)] 9 if (pid == 0) (gdb) next 11 name = "I am the child"; (gdb) next 17 return 0; (gdb) print name$2 = 0x400708 "I am the child"
(gdb)

GDB switched to the child process here.
This can be permanent by adding the setting to the appropriate .gdbinit.
For example, if set follow-fork-mode ask is added to ~/.gdbinit, then ask mode becomes the default mode.

GDB has the ability to debug individual threads, and to manipulate and examine them independently. This functionality is not enabled by default. To do so use set non-stop on  and set target-async on. These can be added to .gdbinit. Once that functionality is turned on, GDB is ready to conduct thread debugging.
For example, the following program creates two threads. These two threads, along with the original thread executing main makes a total of three threads.
#include <stdio.h>
#include <unistd.h>

{
int count3 = 0;

while(count3 < 1000){
sleep(10);
}
return NULL;
}

{
int count2 = 0;

while(count2 < 1000){
}
return NULL;
}

int main (){

int count1 = 0;

while(count1 < 1000){
}

return 0;
}

Compile this program in order to examine it under GDB.
gcc -g three-threads.c -o three-threads  -lpthread
gdb ./three-threads
(gdb) break thread3
Breakpoint 1 at 0x4006c0: file three-threads.c, line 9.
Breakpoint 2 at 0x40070c: file three-threads.c, line 20.
(gdb) break main
Breakpoint 3 at 0x40074a: file three-threads.c, line 30.

Then run the program.
(gdb) run
[...]
Breakpoint 3, main () at three-threads.c:30
[...]
(gdb)


Note that the command info threads provides a summary of the program's threads and some details about their current state. In this case there is only one thread that has been created so far.
Continue execution some more.
(gdb) next
(gdb)
20	  int count2 = 0;
next
34	  int count1 = 0;
(gdb)
9	  int count3 = 0;


Here, two more threads are created. The star indicates the thread currently under focus. Also, the newly created threads have hit the breakpoint set for them in their initialization functions. Namely, thread2() and thread3().
To begin real thread debugging, use the thread <thread number> command to switch the focus to another thread.
(gdb) thread 2
20	  int count2 = 0;
(gdb) list
15	  return NULL;
16	}
17
19	{
20	  int count2 = 0;
21
22	  while(count2 < 1000){
24	  }

(gdb) next
22	  while(count2 < 1000){
(gdb) print count2
$1 = 0 (gdb) next 23 printf("Thread 2: %d\n", count2++); (gdb) next Thread 2: 0 22 while(count2 < 1000){ (gdb) next 23 printf("Thread 2: %d\n", count2++); (gdb) print count2$2 = 1
(gdb)

Above, a few lines of thread2 printed the counter count2 and left thread 2 at line 23 as is seen by the output of 'info threads'.
(gdb) thread 3
9	  int count3 = 0;
(gdb) list
4
6
8	{
9	  int count3 = 0;
10
11	  while(count3 < 1000){
12	    sleep(10);
(gdb)

Thread three is a little different in that it has a sleep statement and executes slowly. Think of it as a representation of an uninteresting IO thread. Since this thread is uninteresting, continue its execution uninterrupted, using the continue.
(gdb) continue &

Take note of the & at the end of the continue. This allows the GDB prompt to return so other commands can be executed. Using the interrupt, execution can be stopped should thread 3 become interesting again.
(gdb) interrupt
[Thread 0x7ffff75d2710 (LWP 4688)] #3 stopped.
0x000000343f4a6a6d in nanosleep () at ../sysdeps/unix/syscall-template.S:82
82	T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)

It is also possible to go back to the original main thread and examine it some more.
(gdb) thread 1
34	  int count1 = 0;
(gdb) next
36	  while(count1 < 1000){
(gdb) next
(gdb) next
36	  while(count1 < 1000){
(gdb) next
(gdb) next
36	  while(count1 < 1000){
(gdb) next
(gdb) next
36	  while(count1 < 1000){
(gdb) print count1
$3 = 3 (gdb) info threads 3 Thread 0x7ffff75d2710 (LWP 4688) 0x000000343f4a6a6d in nanosleep () at ../sysdeps/unix/syscall-template.S:82 2 Thread 0x7ffff7fd3710 (LWP 4687) thread2 (d=0x0) at three-threads.c:23 * 1 Thread 0x7ffff7fd5720 (LWP 4620) main () at three-threads.c:36 (gdb)  As can be seen from the output of info threads, the other threads are where they were left, unaffected by the debugging of thread 1. ### 6.2.6. Alternative User Interfaces for GDB GDB uses the command line as its default interface. However, it also has an API called machine interface (MI). MI allows IDE developers to create other user interfaces to GDB. Some examples of these interfaces are: Eclipse (CDT) A graphical debugger interface integrated with the Eclipse development environment. More information can be found at the Eclipse website. Nemiver A graphical debugger interface which is well suited to the GNOME Desktop Environment. More information can be found at the Nemiver website Emacs A GDB interface which is integrated with the emacs. More information can be found at the Emacs website ### 6.2.7. GDB Documentation For more detailed information about GDB, refer to the GDB manual: Also, the commands info gdb and man gdb will provide more concise information that is up to date with the installed version of gdb. ## 6.3. Variable Tracking at Assignments Variable Tracking at Assignments (VTA) is a new infrastructure included in GCC used to improve variable tracking during optimizations. This allows GCC to produce more precise, meaningful, and useful debugging information for GDB, SystemTap, and other debugging tools. When GCC compiles code with optimizations enabled, variables are renamed, moved around, or even removed altogether. As such, optimized compiling can cause a debugger to report that some variables have been "optimized out". With VTA enabled, optimized code is internally annotated to ensure that optimization passes to transparently keep track of each variable's value, regardless of whether the variable is moved or removed. VTA's benefits are more pronounced when debugging applications with inlined functions. Without VTA, optimization could completely remove some arguments of an inlined function, preventing the debugger from inspecting its value. With VTA, optimization will still happen, and appropriate debugging information will be generated for any missing arguments. VTA is enabled by default when compiling code with optimizations and debugging information enabled. To disable VTA during such builds, add the -fno-var-tracking-assignments. In addition, the VTA infrastructure includes the new gcc option -fcompare-debug. This option tests code compiled by GCC with debug information and without debug information: the test passes if the two binaries are identical. This test ensures that executable code is not affected by any debugging options, which further ensures that there are no hidden bugs in the debug code. Note that -fcompare-debug adds significant cost in compilation time. Refer to man gcc for details about this option. For more information about the infrastructure and development of VTA, refer to A Plan to Fix Local Variable Debug Information in GCC, available at the following link: A slide deck version of this whitepaper is also available at http://people.redhat.com/aoliva/papers/vta/slides.pdf. ## 6.4. Python Pretty-Printers The GDB command print outputs comprehensive debugging information for a target application. GDB aims to provide as much debugging data as it can to users; however, this means that for highly complex programs the amount of data can become very cryptic. In addition, GDB does not provide any tools that help decipher GDB print output. GDB does not even empower users to easily create tools that can help decipher program data. This makes the practice of reading and understanding debugging data quite arcane, particularly for large, complex projects. For most developers, the only way to customize GDB print output (and make it more meaningful) is to revise and recompile GDB. However, very few developers can actually do this. Further, this practice will not scale well, particularly if the developer needs to also debug other programs that are heterogeneous and contain equally complex debugging data. To address this, the Red Hat Enterprise Linux 6 version of GDB is now compatible with Python pretty-printers. This allows the retrieval of more meaningful debugging data by leaving the introspection, printing, and formatting logic to a third-party Python script. Compatibility with Python pretty-printers gives you the chance to truly customize GDB output as you see fit. This makes GDB a more viable debugging solution to a wider range of projects, since you now have the flexibility to adapt GDB output as needed, and with greater ease. Further, developers with intimate knowledge of a project and a specific programming language are best qualified in deciding what kind of output is meaningful, allowing them to improve the usefulness of that output. The Python pretty-printers implementation allows users to automatically inspect, format, and print program data according to specification. These specifications are written as rules implemented via Python scripts. This offers the following benefits: ##### Safe To pass program data to a set of registered Python pretty-printers, the GDB development team added hooks to the GDB printing code. These hooks were implemented with safety in mind: the built-in GDB printing code is still intact, allowing it to serve as a default fallback printing logic. As such, if no specialized printers are available, GDB will still print debugging data the way it always did. This ensures that GDB is backwards-compatible; users who have no need of pretty-printers can still continue using GDB. ##### Highly Customizable This new "Python-scripted" approach allows users to distill as much knowledge as required into specific printers. As such, a project can have an entire library of printer scripts that parses program data in a unique manner specific to its user's needs. There is no limit to the number of printers a user can build for a specific project; what's more, being able to customize debugging data script by script offers users an easier way to re-use and re-purpose printer scripts — or even a whole library of them. ##### Easy to Learn The best part about this approach is its lower barrier to entry. Python scripting is quite easy to learn (in comparison, at least) and has a large library of free documentation available online. In addition, most programmers already have basic to intermediate experience in Python scripting, or in scripting in general. Here is a small example of a pretty printer. Consider the following C++ program: ##### fruit.cc enum Fruits {Orange, Apple, Banana}; class Fruit { int fruit; public: Fruit (int f) { fruit = f; } }; int main() { Fruit myFruit(Apple); return 0; // line 17 }  This is compiled with the command g++ -g fruit.cc -o fruit. Now, examine this program with GDB. gdb ./fruit [...] (gdb) break 17 Breakpoint 1 at 0x40056d: file fruit.cc, line 17. (gdb) run Breakpoint 1, main () at fruit.cc:17 17 return 0; // line 17 (gdb) print myFruit$1 = {fruit = 1}

The output of {fruit = 1} is correct because that is the internal representation of 'fruit' in the data structure 'Fruit'. However, this is not easily read by humans as it is difficult to tell which fruit the integer 1 represents.
To solve this problem, write the following pretty printer:
fruit.py

class FruitPrinter:
def __init__(self, val):
self.val = val

def to_string (self):
fruit = self.val['fruit']

if (fruit == 0):
name = "Orange"
elif (fruit == 1):
name = "Apple"
elif (fruit == 2):
name = "Banana"
else:
name = "unknown"
return "Our fruit is " + name

def lookup_type (val):
if str(val.type) == 'Fruit':
return FruitPrinter(val)
return None

gdb.pretty_printers.append (lookup_type)

Examine this printer from the bottom up.
The line gdb.pretty_printers.append (lookup_type) adds the function lookup_type to GDB's list of printer lookup functions.
The function lookup_type is responsible for examining the type of object to be printed, and returning an appropriate pretty printer. The object is passed by GDB in the parameter val. val.type is an attribute which represents the type of the pretty printer.
FruitPrinter is where the actual work is done. More specifically in the to_string function of that Class. In this function, the integer fruit is retrieved using the python dictionary syntax self.val['fruit']. Then the name is determined using that value. The string returned by this function is the string that will be printed to the user.
After creating fruit.py, it must then be loaded into GDB with the following command:
(gdb) python execfile("fruit.py")
The GDB and Python Pretty-Printers whitepaper provides more details on this feature. This whitepaper also includes details and examples on how to write your own Python pretty-printer as well as how to import it into GDB. Refer to the following link for more information:

## Chapter 7. Profiling

Developers profile programs to focus attention on the areas of the program that have the largest impact on performance. The types of data collected include what section of the program consumes the most processor time, and where memory is allocated. Profiling collects data from the actual program execution. Thus, the quality of the data collect is influenced by the actual tasks being performed by the program. The tasks performed during profiling should be representative of actual use; this ensures that problems arising from realistic use of the program are addressed during development.
Red Hat Enterprise Linux 6 includes a number of different tools (Valgrind, OProfile, perf, and SystemTap) to collect profiling data. Each tool is suitable for performing specific types of profile runs, as described in the following sections.

## 7.1. Profiling In Eclipse

To launch a profile run, navigate to Run > Profile. This will open the Profile As dialogue, from which you can select a tool for a profile run.

To configure each tool for a profile run, navigate to Run > Profile Configuration. This will open the Profile Configuration menu.

For more information on configuring and performing a profile run with each tool in Eclipse, refer to Section 7.2.3, “Valgrind Plug-in for Eclipse ”, and Section 7.3.3, “OProfile Plug-in For Eclipse ”.

## 7.2.  Valgrind

Valgrind is an instrumentation framework for building dynamic analysis tools that can be used to profile applications in detail. Valgrind tools are generally used to automatically detect many memory management and threading problems. The Valgrind suite also includes tools that allow the building of new profiling tools as needed.
Valgrind provides instrumentation for user-space binaries to check for errors, such as the use of uninitialized memory, improper allocation/freeing of memory, and improper arguments for systemcalls. Its profiling tools can be used by normal users on most binaries; however, compared to other profilers, Valgrind profile runs are significantly slower. To profile a binary, Valgrind rewrites its executable and instruments the rewritten binary. Valgrind's tools are most useful for looking for memory-related issues in user-space programs; it is not suitable for debugging time-specific issues or kernel-space instrumentation/debugging.
Previously, Valgrind did not support IBM System z architecture. However, as of 6.1, this support has been added, meaning Valgrind now supports all hardware architectures that are supported by Red Hat Enterprise Linux 6.x.

### 7.2.1. Valgrind Tools

The Valgrind suite is composed of the following tools:
memcheck
This tool detects memory management problems in programs by checking all reads from and writes to memory and intercepting all system calls to malloc, new, free, and delete. Memcheck is perhaps the most used Valgrind tool, as memory management problems can be difficult to detect using other means. Such problems often remain undetected for long periods, eventually causing crashes that are difficult to diagnose.
cachegrind
Cachegrind is a cache profiler that accurately pinpoints sources of cache misses in code by performing a detailed simulation of the I1, D1 and L2 caches in the CPU. It shows the number of cache misses, memory references, and instructions accruing to each line of source code; Cachegrind also provides per-function, per-module, and whole-program summaries, and can even show counts for each individual machine instructions.
callgrind
Like cachegrind, callgrind can model cache behavior. However, the main purpose of callgrind is to record callgraphs data for the executed code.
massif
Massif is a heap profiler; it measures how much heap memory a program uses, providing information on heap blocks, heap administration overheads, and stack sizes. Heap profilers are useful in finding ways to reduce heap memory usage. On systems that use virtual memory, programs with optimized heap memory usage are less likely to run out of memory, and may be faster as they require less paging.
helgrind
In programs that use the POSIX pthreads threading primitives, Helgrind detects synchronisation errors. Such errors are:
• Misuses of the POSIX pthreads API
• Potential deadlocks arising from lock ordering problems
• Data races (i.e. accessing memory without adequate locking)
Valgrind also allows you to develop your own profiling tools. In line with this, Valgrind includes the lackey tool, which is a sample that can be used as a template for generating your own tools.

### 7.2.2. Using Valgrind

The valgrind package and its dependencies install all the necessary tools for performing a Valgrind profile run. To profile a program with Valgrind, use:
valgrind --tool=toolname program
Refer to Section 7.2.1, “Valgrind Tools” for a list of arguments for toolname. In addition to the suite of Valgrind tools, none is also a valid argument for toolname; this argument allows you to run a program under Valgrind without performing any profiling. This is useful for debugging or benchmarking Valgrind itself.
You can also instruct Valgrind to send all of its information to a specific file. To do so, use the option --log-file=filename. For example, to check the memory usage of the executable file hello and send profile information to output, use:
valgrind --tool=memcheck --log-file=output hello
Refer to Section 7.2.4, “Valgrind Documentation” for more information on Valgrind, along with other available documentation on the Valgrind suite of tools.

### 7.2.3. Valgrind Plug-in for Eclipse

The Valgrind plug-in for Eclipse (documented herein) integrates several Valgrind tools into Eclipse. This allows Eclipse users to seamlessly include profiling capabilities into their workflow. At present, the Valgrind plug-in for Eclipse supports three Valgrind tools:
• Memcheck
• Massif
• Cachegrind
The Valgrind plug-in for Eclipse is provided by the eclipse-valgrind package. For more information about this plug-in, refer to Valgrind Integration User Guide in the Eclipse Help Contents.

### 7.2.4. Valgrind Documentation

For more extensive information on Valgrind, refer to man valgrind. Red Hat Enterprise Linux 6 also provides a comprehensive Valgrind Documentation book, available as PDF and HTML in:
• file:///usr/share/doc/valgrind-version/valgrind_manual.pdf
• file:///usr/share/doc/valgrind-version/html/index.html
The Valgrind Integration User Guide in the Eclipse Help Contents also also provides detailed information on the setup and usage of the Valgrind plug-in for Eclipse. This guide is provided by the eclipse-valgrind package.

## 7.3. OProfile

OProfile is a system-wide Linux profiler, capable of running at low overhead. It consists of a kernel driver and a daemon for collecting raw sample data, along with a suite of tools for parsing that data into meaningful information. OProfile is generally used by developers to determine which sections of code consume the most amount of CPU time, and why.
During a profile run, OProfile uses the processor's performance monitoring hardware. Valgrind rewrites the binary of an application, and in turn instruments it. OProfile, on the other hand,simply profiles a running application as-is. It sets up the performance monitoring hardware to take a sample every x number of events (e.g. cache misses or branch instructions). Each sample also contains information on where it occurred in the program.
OProfile's profiling methods consume less resources than Valgrind. However, OProfile requires root privileges. OProfile is useful for finding "hot-spots" in code, and looking for their causes (e.g. poor cache performance, branch mispredictions).
Using OProfile involves starting the OProfile daemon (oprofiled), running the program to be profiled, collecting the system profile data, and parsing it into a more understandable format. OProfile provides several tools for every step of this process.

### 7.3.1. OProfile Tools

The most useful OProfile commands include the following:
opcontrol
This tool is used to start/stop the OProfile daemon and configure a profile session.
opreport
The opreport command outputs binary image summaries, or per-symbol data, from OProfile profiling sessions.
opannotate
The opannotate command outputs annotated source and/or assembly from the profile data of an OProfile session.
oparchive
The oparchive command generates a directory populated with executable, debug, and OProfile sample files. This directory can be moved to another machine (via tar), where it can be analyzed offline.
opgprof
Like opreport, the opgprof command outputs profile data for a given binary image from an OProfile session. The output of opgprof is in gprof format.
For a complete list of OProfile commands, refer to man oprofile. For detailed information on each OProfile command, refer to its corresponding man page. Refer to Section 7.3.4, “OProfile Documentation” for other available documentation on OProfile.

### 7.3.2. Using OProfile

The oprofile package and its dependencies install all the necessary utilities for performing an OProfile profile run. To instruct the OProfile to profile all the application running on the system and to group the samples for the shared libraries with the application using the library, run the following command as root:
opcontrol --no-vmlinux --separate=library --start
You can also start the OProfile daemon without collecting system data. To do so, use the option --start-daemon instead. The --stop option halts data collection, while the --shutdown terminates the OProfile daemon.
Use opreport, opannotate, or opgprof to display the collected profiling data. By default, the data collected by the OProfile daemon is stored in /var/lib/oprofile/samples/.

### 7.3.3. OProfile Plug-in For Eclipse

The OProfile suite of tools provide powerful call profiling capabilities; as a plug-in, these capabilities are well ported into the Eclipse user interface. The OProfile Plug-in provides the following benefits:
##### Targeted Profiling
The OProfile Plug-in will allow Eclipse users to profile a specific binary, include related shared libraries/kernel modules, and even exclude binaries. This produces very targeted, detailed usage results on each binary, function, and symbol, down to individual line numbers in the source code.
##### User Interface Fully Integrated into CDT
The plug-in displays enriched OProfile results through Eclipse, just like any other plug-in. Double-clicking on a source line in the results brings users directly to the corresponding line in the Eclipse editor. This allows users to build, profile, and edit code through a single interface, making profiling a convenient experience for Eclipse users. In addition, profile runs are launched and configured the same way as C/C++ applications within Eclipse.
##### Fully Customizable Profiling Options
The Eclipse interface allows users to configure their profile run using all options available in the OProfile command-line utility. The plug-in supports event configuration based on processor debugging registers (i.e. counters), as well as interrupt-based profiling for kernels or processors that don't support hardware counters.
##### Ease of Use
The OProfile Plug-in provides generally useful defaults for all options, usable for a majority of profiling runs. In addition, it also features a "one-click profile" that executes a profile run using these defaults. Users can profile applications from start to finish, or select specific areas of code through a manual control dialog.
The OProfile plug-in for Eclipse is provided by the eclipse-oprofile package. For more information about this plug-in, refer to OProfile Integration User Guide in the Eclipse Help Contents (also provided by eclipse-profile).

### 7.3.4. OProfile Documentation

For a more extensive information on OProfile, refer to man oprofile. Red Hat Enterprise Linux 6 also provides two comprehensive guides to OProfile in file:///usr/share/doc/oprofile-version/:
OProfile Manual
A comprehensive manual with detailed instructions on the setup and use of OProfile is found at file:///usr/share/doc/oprofile-version/oprofile.html
OProfile Internals
Documentation on the internal workings of OProfile, useful for programmers interested in contributing to the OProfile upstream, can be found at file:///usr/share/doc/oprofile-version/internals.html
The OProfile Integration User Guide in the Eclipse Help Contents also provides detailed information on the setup and usage of the OProfile plug-in for Eclipse. This guide is provided by the eclipse-oprofile package.

## 7.4. SystemTap

SystemTap is a useful instrumentation platform for probing running processes and kernel activity on the Linux system. To execute a probe:
1. Write SystemTap scripts that specify which system events (e.g. virtual file system reads, packet transmissions) should trigger specified actions (e.g. print, parse, or otherwise manipulate data).
2. SystemTap translates the script into a C program, which it compiles into a kernel module.
3. SystemTap loads the kernel module to perform the actual probe.
SystemTap scripts are useful for monitoring system operation and diagnosing system issues with minimal intrusion into the normal operation of the system. You can quickly instrument running system test hypotheses without having to recompile and re-install instrumented code. To compile a SystemTap script that probes kernel-space, SystemTap uses information from three different kernel information packages:
• kernel-variant-devel-version
• kernel-variant-debuginfo-version
• kernel-variant-debuginfo-common-arch-version

## Difference between Red Hat Enterprise Linux 5 and 6

The kernel information package in Red Hat Enterprise Linux 6 is now named kernel-variant-debuginfo-common-arch-version. It was originally kernel-variant-debuginfo-common-version in Red Hat Enterprise Linux 5.
These kernel information packages must match the kernel to be probed. In addition, to compile SystemTap scripts for multiple kernels, the kernel information packages of each kernel must also be installed.
An important new feature has been added as of Red Hat Enterprise Linux 6.1: the --remote option. This allows users to build the SystemTap module locally, and then execute it remotely via SSH. The syntax to use this is --remote [USER@]HOSTNAME; set the execution target to the specified SSH host, optionally using a different username. This option may be repeated to target multiple execution targets. Passes 1-4 are completed locally as normal to build the scrip, and then pass 5 copies the module to the target and runs it.
The following sections describe other new SystemTap features available in the Red Hat Enterprise Linux 6 release.

### 7.4.1. SystemTap Compile Server

SystemTap in Red Hat Enterprise Linux 6 supports a compile server and client deployment. With this setup, the kernel information packages of all client systems in the network are installed on just one compile server host (or a few). When a client system attempts to compile a kernel module from a SystemTap script, it remotely accesses the kernel information it needs from the centralized compile server host.
A properly configured and maintained SystemTap compile server host offers the following benefits:
• The system administrator can verify the integrity of kernel information packages before making the packages available to users.
• The identity of a compile server can be authenticated using the Secure Socket Layer (SSL). SSL provides an encrypted network connection that prevents eavesdropping or tampering during transmission.
• Individual users can run their own servers and authorize them for their own use as trusted.
• System administrators can authorize one or more servers on the network as trusted for use by all users.
• A server that has not been explicitly authorized is ignored, preventing any server impersonations and similar attacks.

### 7.4.2. SystemTap Support for Unprivileged Users

For security purposes, users in an enterprise setting are rarely given privileged (i.e. root or sudo) access to their own machines. In addition, full SystemTap functionality should also be restricted to privileged users, as this can provide the ability to completely take control of a system.
SystemTap in Red Hat Enterprise Linux 6 features a new option to the SystemTap client: --unprivileged. This option allows an unprivileged user to run stap. Of course, several restrictions apply to unprivileged users that attempt to run stap.

## Note

An unprivileged user is a member of the group stapusr but is not a member of the group stapdev (and is not root).
Before loading any kernel modules created by unprivileged users, SystemTap verifies the integrity of the module using standard digital (cryptographic) signing techniques. Each time the --unprivileged option is used, the server checks the script against the constraints imposed for unprivileged users. If the checks are successful, the server compiles the script and signs the resulting module using a self-generated certificate. When the client attempts to load the module, staprun first verifies the signature of the module by checking it against a database of trusted signing certificates maintained and authorized by root.
Once a signed kernel module is successfully verified, staprun is assured that:
• The module was created using a trusted systemtap server implementation.
• The module was compiled using the --unprivileged option.
• The module meets the restrictions required for use by an unprivileged user.
• The module has not been tampered with since it was created.

### 7.4.3.  SSL and Certificate Management

SystemTap in Red Hat Enterprise Linux 6 implements authentication and security via certificates and public/private key pairs. It is the responsibility of the system administrator to add the credentials (i.e. certificates) of compile servers to a database of trusted servers. SystemTap uses this database to verify the identity of a compile server that the client attempts to access. Likewise, SystemTap also uses this method to verify kernel modules created by compile servers using the --unprivileged option.

#### 7.4.3.1. Authorizing Compile Servers for Connection

The first time a compile server is started on a server host, the compile server automatically generates a certificate. This certificate verifies the compile server's identity during SSL authentication and module signing.
In order for clients to access the compile server (whether on the same server host or from a client machine), the system administrator must add the compile server's certificate to a database of trusted servers. Each client host intending to use compile servers maintains such a database. This allows individual users to customize their database of trusted servers, which can include a list of compile servers authorized for their own use only.

#### 7.4.3.2. Authorizing Compile Servers for Module Signing (for Unprivileged Users)

Unprivileged users can only load signed, authorized SystemTap kernel modules. For modules to be recognized as such, they have to be created by a compile server whose certificate appears in a database of trusted signers; this database must be maintained on each host where the module will be loaded.

#### 7.4.3.3. Automatic Authorization

Servers started using the stap-server initscript are automatically authorized to receive connections from all clients on the same host.
Servers started by other means are automatically authorized to receive connections from clients on the same host run by the user who started the server. This was implemented with convenience in mind; users are automatically authorized to connect to a server they started themselves, provided that both client and server are running on the same host.
Whenever root starts a compile server, all clients running on the same host automatically recognize the server as authorized. However, Red Hat advises that you refrain from doing so.
Similarly, a compile server initiated through stap-server is automatically authorized as a trusted signer on the host in which it runs. If the compile server was initiated through other means, it is not automatically authorized as such.

### 7.4.4. SystemTap Documentation

For more detailed information about SystemTap, refer to the following books (also provided by Red Hat):
• SystemTap Beginner's Guide
• SystemTap Tapset Reference
• SystemTap Language Reference (documentation supplied by IBM)
The SystemTap Beginner's Guide and SystemTap Tapset Reference are also available locally when you install the systemtap package:
• file:///usr/share/doc/systemtap-version/SystemTap_Beginners_Guide/index.html
• file:///usr/share/doc/systemtap-version/SystemTap_Beginners_Guide.pdf
• file:///usr/share/doc/systemtap-version/tapsets/index.html
• file:///usr/share/doc/systemtap-version/tapsets.pdf
The Section 7.4.1, “SystemTap Compile Server”, Section 7.4.2, “SystemTap Support for Unprivileged Users”, and Section 7.4.3, “ SSL and Certificate Management” sections are excerpts from the SystemTap Support for Unprivileged Users and Server Client Deployment whitepaper. This whitepaper also provides more details on each feature, along with a case study to help illustrate their application in a real-world environment.

## 7.5. Performance Counters for Linux (PCL) Tools and perf

Performance Counters for Linux (PCL) is a new kernel-based subsystem that provides a framework for collecting and analyzing performance data. These events will vary based on the performance monitoring hardware and the software configuration of the system. Red Hat Enterprise Linux 6 includes this kernel subsystem to collect data and the user-space tool perf to analyze the collected performance data.
The PCL subsystem can be used to measure hardware events, including retired instructions and processor clock cycles. It can also measure software events, including major page faults and context switches. For example, PCL counters can compute the Instructions Per Clock (IPC) from a process's counts of instructions retired and processor clock cycles. A low IPC ratio indicates the code makes poor use of the CPU. Other hardware events can also be used to diagnose poor CPU performance.
Performance counters can also be configured to record samples. The relative frequency of samples can be used to identify which regions of code have the greatest impact on performance.

### 7.5.1. Perf Tool Commands

Useful perf commands include the following:
perf stat
This perf command provides overall statistics for common performance events, including instructions executed and clock cycles consumed. Options allow selection of events other than the default measurement events.
perf record
This perf command records performance data into a file which can be later analyzed using perf report.
perf report
This perf command reads the performance data from a file and analyzes the recorded data.
perf list
This perf command lists the events available on a particular machine. These events will vary based on the performance monitoring hardware and the software configuration of the system.
Use perf help to obtain a complete list of perf commands. To retrieve man page information on each perf command, use perf help command.

### 7.5.2. Using Perf

Using the basic PCL infrastructure for collecting statistics or samples of program execution is relatively straightforward. This section provides simple examples of overall statistics and sampling.
To collect statistics on make and its children, use the following command:
perf stat -- make all
The perf command will collect a number of different hardware and software counters. It will then print the following information:
Performance counter stats for 'make all':

53328  context-switches         #      0.000 M/sec
515  CPU-migrations           #      0.000 M/sec
1843121  page-faults              #      0.008 M/sec
789702529782  cycles                   #   3236.330 M/sec
1050912611378  instructions             #      1.331 IPC
275538938708  branches                 #   1129.203 M/sec
2888756216  branch-misses            #      1.048 %
4343060367  cache-references         #     17.799 M/sec
428257037  cache-misses             #      1.755 M/sec

263.779192511  seconds time elapsed

The perf tool can also record samples. For example, to record data on the make command and its children, use:
perf record -- make all
This will print out the file in which the samples are stored, along with the number of samples collected:
[ perf record: Woken up 42 times to write data ]
[ perf record: Captured and wrote 9.753 MB perf.data (~426109 samples) ]

You can then analyze perf.data to determine the relative frequency of samples. The report output includes the command, object, and function for the samples. Use perf report to output an analysis of perf.data. For example, the following command produces a report of the executable that consumes the most time:
perf report --sort=comm
The resulting output:
# Samples: 1083783860000
#
# ........  ...............
#
48.19%         xsltproc
44.48%        pdfxmltex
6.01%             make
0.95%             perl
0.17%       kernel-doc
0.05%          xmllint
0.05%              cc1
0.03%               cp
0.01%            xmlto
0.01%               sh
0.01%          docproc
0.01%               ld
0.01%              gcc
0.00%               rm
0.00%              sed
0.00%   git-diff-files
0.00%             bash
0.00%   git-diff-index

The column on the left shows the relative frequency of the samples. This output shows that make spends most of this time in xsltproc and the pdfxmltex. To reduce the time for the make to complete, focus on xsltproc and pdfxmltex. To list of the functions executed by xsltproc, run:
perf report -n --comm=xsltproc
This would generate:
comm: xsltproc
# Samples: 472520675377
#
# Overhead  Samples                    Shared Object  Symbol
# ........ ..........  .............................  ......
#
45.54%215179861044  libxml2.so.2.7.6               [.] xmlXPathCmpNodesExt
8.60%40634845107  libxml2.so.2.7.6               [.] xmlXPathCompOpEval
4.63%21864091080  libxml2.so.2.7.6               [.] xmlXPathReleaseObject
2.73%12919672281  libxml2.so.2.7.6               [.] xmlXPathNodeSetSort__internal_alias
2.60%12271959697  libxml2.so.2.7.6               [.] valuePop
2.41%11379910918  libxml2.so.2.7.6               [.] xmlXPathIsNaN__internal_alias
2.19%10340901937  libxml2.so.2.7.6               [.] valuePush__internal_alias


## 7.6. ftrace

The ftrace framework provides users with several tracing capabilities, accessible through an interface much simpler than SystemTap's. This framework uses a set of virtual files in the debugfs file system; these files enable specific tracers. The ftrace function tracer simply outputs each function called in the kernel in real time; other tracers within the ftrace framework can also be used to analyze wakeup latency, task switches, kernel events, and the like.
You can also add new tracers for ftrace, making it a flexible solution for analyzing kernel events. The ftrace framework is useful for debugging or analyzing latencies and performance issues that take place outside of user-space. Unlike other profilers documented in this guide, ftrace is a built-in feature of the kernel.

### 7.6.1. Using ftrace

The Red Hat Enterprise Linux 6 kernels have been configured with the CONFIG_FTRACE=y option. This option provides the interfaces needed by ftrace. To use ftrace, mount the debugfs file system as follows:
mount -t debugfs nodev /sys/kernel/debug
All the ftrace utilities are located in /sys/kernel/debug/tracing/. View the /sys/kernel/debug/tracing/available_tracers file to find out what tracers are available for your kernel:
cat /sys/kernel/debug/tracing/available_tracers
power wakeup irqsoff function sysprof sched_switch initcall nop
To use a specific tracer, write it to /sys/kernel/debug/tracing/current_tracer. For example, wakeup traces and records the maximum time it takes for the highest-priority task to be scheduled after the task wakes up. To use it:
echo wakeup > /sys/kernel/debug/tracing/current_tracer
To start or stop tracing, write to /sys/kernel/debug/tracing/tracing_on, as in:
echo 1 > /sys/kernel/debug/tracing/tracing_on (enables tracing)
echo 0 > /sys/kernel/debug/tracing/tracing_on (disables tracing)
The results of the trace can be viewed from the following files:
/sys/kernel/debug/tracing/trace
This file contains human-readable trace output.
/sys/kernel/debug/tracing/trace_pipe
This file contains the same output as /sys/kernel/debug/tracing/trace, but is meant to be piped into a command. Unlike /sys/kernel/debug/tracing/trace, reading from this file consumes its output.

### 7.6.2. ftrace Documentation

The ftrace framework is fully documented in the following files:
• ftrace - Function Tracer: file:///usr/share/doc/kernel-doc-version/Documentation/trace/ftrace.txt
• function tracer guts: file:///usr/share/doc/kernel-doc-version/Documentation/trace/ftrace-design.txt

## Chapter 8.  Documentation Tools

Red Hat Enterprise Linux 6 has two documentation tools available to include documentation with a project. These are Publican and Doxygen.

## 8.1. Publican

Publican a program is used to publish and process documentation through DocBook XML. In the process of publishing books, it checks the XML to ensure it is valid and in a publishable standard. It is particularly useful for publishing the documentation accompanying a newly created application.

### 8.1.1. Commands

Publican has a vast number of commands and actions available, all of which can be found in the --help or --man pages. The most common ones are:
build
Converts the XML files into other formats more suitable for documentation (PDF, HTML, HTML-single, for example).
create
Creates a new book, including all the required files as discussed in Section 8.1.3, “Files”.
create_brand
Creates a new brand, allowing all books to look the same, as discussed in Section 8.1.6, “Brands”.
package
Packages the files of a book into an RPM ready to distribute.

### 8.1.2. Create a New Document

Use the publican create command to create a new document including all the required files.
There are a number of options available to append to the publican create. These are:
--help
Prints a list of accepted options for the publican create command.
--name Doc_Name
Set the name of the book. Keep in mind that the title must contain no spaces.
--lang Language_Code
If this is not set, the default is en-US. However, The --lang option sets the xml_lang in the publican.cfg file and creates a directory with this name in the document directory.
--version version
Set the version number of the product the book is about.
--product Product_Name
Set the name of the product the book is about. Keep in mind that this must contain no spaces.
--brand brand
Set the name of a brand to use to keep the look of the documents consistant.
Refer to --help for more options.
Remember to change into the directory the book is to be created in before running publican create lest the files and directories be added to the user's home directory.

### 8.1.3. Files

When a book is made, a number of files are created in the book's directory. These files are required for the book to be built properly and should not be deleted. They are, however, required to be edited for links (such as chapters) to work, as well as to contain the correct information regarding authors and titles etc. These files are:
publican.cfg
This file configures the build options and always includes the parameters xml_lang (the language the book is in, en-US for example), type (the type of document, a book or a set, for example), and brand (the branding the document uses, found here: Section 8.1.6, “Brands”. Red Hat, for example.). There are a number of optional parameters but these should be used cautiously as they can cause problems further on in areas like translation. A full list of these advanced parameters can be found in the Publican User Guide. The publican.cfg file is unlikely to be edited much beyond the initial creation.
book_info.xml
This file is essentially the template of the book. It contains information such as the title, subtitle, author, publication number, and the book's ID number. It also contains the basic Publican information printed at the beginning of each publication with information on the notes, cautions, and warnings as well as a basic stylistic guide. This file will be edited often as every time a book is updated the publication number needs to be incremented.
Author_Group.xml
This file is used to store information about the authors and contributors. Once initially set up it is unlikely further editing will be needed unless a change of authorship occurs.
Chapter.xml
This file is an example of what the actual content will be. It is created as a place holder but unless it is linked in the Doc_Name.xml (below) it will not appear in the actual book. When writing content for the publication, new XML files are created, named appropriately (ch-publican.xml, for example) and linked in Doc_Name.xml. When the book is built, the content of this file will form the content of the book. This specific file is unlikely to ever be edited but others like it will be edited constantly as content is changed, updated, added to or removed.
Doc_Name.xml
This file is essentially the contents page of the publication. It contains a list of links to the various chapters a book is to contain. Naturally it won't actually be called 'Doc_Name' but will have whatever the title of the publication is in it's place (Developer_Guide.xml, for example). This will only be edited when new chapters are added, removed or rearranged. This must remain the same as Doc_Name.ent or the book will not build.
Doc_Name.ent
This file contains a list of local entities. By default YEAR is set to the current year and HOLDER has a reminder to place the copyright owner's name there. As with Doc_Name.xml, this file will not be called 'Doc_Name' but will be replaced with the title of the document (Developer_Guide.ent, for example). This is only likely to be edited once at the beginning of publication or if the copyright owner changes. This must remain the same as Doc_Name.xml or the book will not build.
Revision_History.xml
When publican package is run, the first XML file containing a <revhistory> tag is used to build the RPM revision history.

#### 8.1.3.1. Adding Media to Documentation

Occasionally it may become necessary to add various media to a document in order to illustrate what is being explained.
##### Images
The images folder is created by publican in the document's directory. Store any images used in the document here. Then when entering an image into the document, link to the image inside the images directory (./images/image1.png, for example).
##### Code Examples
As time passes and technology changes, a project's documentation will need to be updated to reflect differences in code. To make this easier, create individual files for each code example in a preferred editor, then save them in a folder called extras in the document's directory. Then, when entering the code sample into the document, link to the file and the folder it is in. This way an example used in several places can be updated only once, and rather than search through a document looking for a specific item to change, all the code examples are located in the one place, saving time and effort.
##### Arbitrary Files
On occasion there may be a need for files not attached to the documentation to be bundled with the RPM (video tutorials, for example). Adding these files to a directory called files in the publication's directory will allow them to be added to the RPM when the book is compiled.
To link to any of these files, use the following XML:
<xi:include parse="text" href="extras/fork/fork1.c" xmlns:xi="http://www.w3.org/2001/XInclude" />


### 8.1.4. Building a Document

In the root directory, first run a test build to ensure that all the XML is correct and acceptable by typing publican build --formats=chosen_format --langs=chosen_language. For example, to build a document in US English and as a single HTML page, run publican build --formats=html-single --langs=en-US. Provided there are no errors the book will be built into the root directory where the pages can be viewed to see if it has the look required. It is recommended to do this regularly in order to make troubleshooting as easy as possible.

## --novalid Command

When creating a build to test for any bugs in the XML code, sometimes it may be useful to use the --novalid option. This skips over any cross-references and links that point to files or sections of the document that do not yet exist. Instead they are shown as three question marks (???).
There are a number of different formats a document can be published in. These are:
html
An ordinary HTML page with links to new pages for new chapters and sections.
html-single
One long HTML page where the links to new chapters and sections at the top of the page directing the user further down the page, rather than to new page.
html-desktop
One long HTML page where the links to new chapters and sections are in a panel on the left side of the document, directing the user further down the page, rather than to a new page.
man
A man page for Linux, UNIX, and other similar operating systems.
pdf
A PDF file.
test
The XML is validated without actually creating a file for viewing.
txt
A single text file.
epub
An e-book in EPUB format.
eclipse
An Eclipse help plug-in.

### 8.1.5. Packaging a Publication

Once the documentation is complete and can be built with no errors, run publican package --lang=chosen_language. This will output SRPM packages to tmp/rpm in the document's directory, and binary RPM packages will go to tmp/rpm/noarch in the document's directory. By default, these packages are named productname-title-productnumber-[web]-language-edition-pubsnumber.[build_target].noarch.file_extension with the information for each of these sections coming from publican.cfg.

### 8.1.6. Brands

Brands are used in a similar way as templates in that they create a level of consistency in appearance, with aspects like matching logos, images and color schemes, across a range of documents. This can be particularly useful when producing several books for the same application or the same bundle of applications.
In order to create a new brand, it must have a name and a language. Run publican create_brand --name=brand --lang=language_code. This will create a folder called publican-brand and place it in the publication's directory. This folder contains the following files:
COPYING
Part of an SRPM package and containing the copyright license and details.
defaults.cfg
Provides default values for the parameters that can be set in publican.cfg. Specifications from this file are applied first before applying those in the publican.cfg file. Therefore, values in the publican.cfg file over ride those in the defaults.cfg file. It is best used for aspects that are routinely used throughout the documents but still allows writers to change settings.
overrides.cfg
Also provides values for the parameters that can be set in publican-brand.spec. Specifications from this file are applied last, thus overriding both the defaults.cfg and the publican.cfg. It is best used for aspects the writers are not allowed to change.
publican.cfg
This file is similar to the publican.cfg file for a publication in that it configures basic information for the brand, such as version, release number and brand name.
publican-brand.spec
This file is used by the RPM Package Manager to package the publication into an RPM.
README
Part of an SRPM package and providing a brief description of the package.
A subdirectory, named by the language code, is also placed in this directory and contains the following files:
Feedback.xml
This is generated by default to allow readers to leave feedback. Customize it to contain the relevant contact details or a bug reporting process.
Legal_Notice.xml:
Two more subdirectories are within this directory. The images subdirectory contains a number of images of both raster (PNG) and vector (SVG) formats and serve as place holders for various navigation icons that can be changed simply by replacing the images. The css folder contains overrides.css, which sets the visual style for the brand, overriding those in common.css.
In order to package the new brand ready for distribution, use the publican package command. By default this creates source RPM packages (SRPM Packages) but it can also create binary RPM packages using the option --binary. Packages are named publican-brand-version-release.[build_target].[noarch].file_extension with the required parameters taken from the publican.cfg file.

## File Extensions

SRPM packages have the file extension .src.rpm while binary RPM packages have the file extension .rpm
Binary RPM packages include [build_target].noarch before the file extension, where [build_target] represents the operating system and version that the package is built for as set by the os_ver parameter in the publican.cfg file. The noarch element specifies that the package can be installed on any system, regardless of the system architecture.

### 8.1.7. Building a Website

Publican can also build websites to manage documentation. This is mostly useful when only one person is maintaining the documentation, but where a team is working on the documentation Publican can generate RPM packages of documentation to install on a web server. The website created consists of a homepage, product and version description pages, and the pages for the documentation. In the publication's root directory, Publican creates a configuration file, an SQLite database file, and two subdirectories. There could be many configuration files depending on how many languages the documentation is published in, with a new subdirectory for each language.

### 8.1.8. Documentation

Publican has comprehensive --man, --help and --help_actions pages accessed from the terminal.
For information on XML including the different tags available, see the DocBook guide, DocBook: the definitive guide by Norman Walsh and Leonard Muellner, found here: http://www.docbook.org/tdg/en/html/docbook and specifically Part II: Reference for a list of all the tags and brief instructions on how to use them.
There is also the comprehensive Publican User Guide accessed online at http://jfearn.fedorapeople.org/en-US/index.html or installed locally with yum install publican-doc.

## 8.2. Doxygen

Doxygen is a documentation tool that creates reference material both online in HTML and offline in Latex. It does this from a set of documented source files which makes it easy to keep the documentation consistent and correct with the source code.

### 8.2.1. Doxygen Supported Output and Languages

Doxygen has support for output in:
• RTF (MS Word)
• PostScript
• Compressed HTML
• Unix man pages
Doxygen supports the following programming languages:
• C
• C++
• C#
• Objective -C
• IDL
• Java
• VHDL
• PHP
• Python
• Fortran
• D

### 8.2.2. Getting Started

Doxygen uses a configuration file to determine its settings, therefore it is paramount that this be created correctly. Each project needs its own configuration file. The most painless way to create the configuration file is with the command doxygen -g config-file. This creates a template configuration file that can be easily edited. The variable config-file is the name of the configuration file. If it is committed from the command it is simply called Doxyfile by default. Another useful option while creating the configuration file is the use of a minus sign (-) as the file name. This is useful for scripting as it will cause Doxygen to attempt to read the configuration file from standard input (stdin).
The configuration file consists of a number of variables and tags, similar to a simple Makefile. For example:
TAGNAME = VALUE1 VALUE2...
For the most part these can be left alone but should the need arise to edit them refer to the configuration page of the Doxygen documentation website for an extensive explanation of all the tags available. There is also a GUI interface called doxywizard. If this is the preferred method of editing then documentation for this function can be found on the Doxywizard usage page of the Doxygen documentation website.
There are eight tags that are useful to become familiar with.
##### INPUT
For small projects consisting mainly of C or C++ source and header files there is no need to change things. However, if the project is large and consists of a source directory or tree, then assign the root directory or directories to the INPUT tag.
##### FILE_PATTERNS
File patterns (for example, *.cpp or *.h) can be added to this tag allowing only files that match one of the patterns to be parsed.
##### RECURSIVE
Setting this to yes will allow recursive parsing of a source tree.
##### EXCLUDE and EXCLUDE_PATTERNS
These are used to further fine-tune the files that are parsed by adding file patterns to avoid. For example, to omit all test directories from a source tree, use EXCLUDE_PATTERNS = */test/*.
##### EXTRACT_ALL
When this is set to yes, doxygen will pretend that everything in the source files is documented to give an idea of how a fully documented project would look. However, warnings regarding undocumented members will not be generated in this mode; set it back to no when finished to correct this.
##### SOURCE_BROWSER and INLINE_SOURCES
By setting the SOURCE_BROWSER tag to yes doxygen will generate a cross-reference to analyze a piece of software's definition in its source files with the documentation existing about it. These sources can also be included in the documentation by setting INLINE_SOURCES to yes.

### 8.2.3. Running Doxygen

Running doxygen config-file creates html, rtf, latex, xml, and / or man directories in whichever directory doxygen is started in, containing the documentation for the corresponding filetype.
##### HTML OUTPUT
This documentation can be viewed with a HTML browser that supports cascading style sheets (CSS), as well as DHTML and Javascript for some sections. Point the browser (for example, Mozilla, Safari, Konqueror, or Internet Explorer 6) to the index.html in the html directory.
##### LaTeX OUTPUT
Doxygen writes a Makefile into the latex directory in order to make it easy to first compile the Latex documentation. To do this, use a recent teTeX distribution. What is contained in this directory depends on whether the USE_PDFLATEX is set to no. Where this is true, typing make while in the latex directory generates refman.dvi. This can then be viewed with xdvi or converted to refman.ps by typing make ps. Note that this requires dvips.
There are a number of commands that may be useful. The command make ps_2on1 prints two pages on one physical page. It is also possible to convert to a PDF if a ghostscript interpreter is installed by using the command make pdf. Another valid command is make pdf_2on1. When doing this set PDF_HYPERLINKS and USE_PDFLATEX tags to yes as this will cause Makefile will only contain a target to build refman.pdf directly.
##### RTF OUTPUT
This file is designed to import into Microsoft Word by combining the RTF output into a single file: refman.rtf. Some information is encoded using fields but this can be shown by selecting all (CTRL+A or Edit -> select all) and then right-click and select the toggle fields option from the drop down menu.
##### XML OUTPUT
The output into the xml directory consists of a number of files, each compound gathered by doxygen, as well as an index.xml. An XSLT script, combine.xslt, is also created that is used to combine all the XML files into a single file. Along with this, two XML schema files are created, index.xsd for the index file, and compound.xsd for the compound files, which describe the possible elements, their attributes, and how they are structured.
##### MAN PAGE OUTPUT
The documentation from the man directory can be viewed with the man program after ensuring the manpath has the correct man directory in the man path. Be aware that due to limitations with the man page format, information such as diagrams, cross-references and formulas will be lost.

### 8.2.4. Documenting the Sources

There are three main steps to document the sources.
1. First, ensure that EXTRACT_ALL is set to no so warnings are correctly generated and documentation is built properly. This allows doxygen to create documentation for documented members, files, classes and namespaces.
2. There are two ways this documentation can be created:
A special documentation block
This comment block, containing additional marking so Doxygen knows it is part of the documentation, is in either C or C++. It consists of a brief description, or a detailed description. Both of these are optional. What is not optional, however, is the in body description. This then links together all the comment blocks found in the body of the method or function.

## Concurrent brief or detailed descriptions

While more than one brief or detailed descriptions is allowed, this is not recommended as the order is not specified.
The following will detail the ways in which a comment block can be marked as a detailed description:
• C-style comment block, starting with two asterisks (*) in the JavaDoc style.
/**
* ... documentation ...
*/

• C-style comment block using the Qt style, consisting of an exclamation mark (!) instead of an extra asterisks.
/*!
* ... documentation ...
*/

• The beginning asterisks on the documentation lines can be left out in both cases if that is preferred.
• A blank beginning and end line in C++ also acceptable, with either three forward slashes or two forward slashes and an exclamation mark.
///
/// ... documentation
///

or
//!
//! ... documentation ...
//!

• Alternatively, in order to make the comment blocks more visible a line of asterisks or forward slashes can be used.
/////////////////////////////////////////////////
/// ... documentation ...
/////////////////////////////////////////////////

or
/********************************************//**
* ... documentation ...
***********************************************/

Note that the two forwards slashes at the end of the normal comment block start a special comment block.
There are three ways to add a brief description to documentation.
• To add a brief description use \brief above one of the comment blocks. This brief section ends at the end of the paragraph and any further paragraphs are the detailed descriptions.
/*! \brief brief documentation.
*         brief documentation.
*
*  detailed documentation.
*/

• By setting JAVADOC_AUTOBRIEF to yes, the brief description will only last until the first dot followed by a space or new line. Consequentially limiting the brief description to a single sentence.
/** Brief documentation. Detailed documentation continues * from here.
*/

This can also be used with the above mentioned three-slash comment blocks (///).
• The third option is to use a special C++ style comment, ensuring this does not span more than one line.
/// Brief documentation.
/** Detailed documentation. */

or
//! Brief documentation.

//! Detailed documentation //! starts here
The blank line in the above example is required to separate the brief description and the detailed description, and JAVADOC_AUTOBRIEF needs to be set to no.
Examples of how a documented piece of C++ code using the Qt style can be found on the Doxygen documentation website
It is also possible to have the documentation after members of a file, struct, union, class, or enum. To do this add a < marker in the comment block.\
int var; /*!< detailed description after the member */

Or in a Qt style as:
int var; /**< detailed description after the member */

or
int var; //!< detailed description after the member
//!<

or
int var; ///< detailed description after the member
///<

For brief descriptions after a member use:
int var; //!< brief description after the member
or
int var; ///< brief description after the member
Examples of these and how the HTML is produced can be viewed on the Doxygen documentation website
Documentation at other places
While it is preferable to place documentation in front of the code it is documenting, at times it is only possible to put it in a different location, especially if a file is to be documented; after all it is impossible to place the documentation in front of a file. This is best avoided unless it is absolutely necessary as it can lead to some duplication of information.
To do this it is important to have a structural command inside the documentation block. Structural commands start with a backslash (\) or an at-sign (@) for JavaDoc and are followed by one or more parameters.
/*! \class Test
\brief A test class.

A more detailed description of class.
*/

In the above example the command \class is used. This indicates that the comment block contains documentation for the class 'Test'. Others are:
• \struct: document a C-struct
• \union: document a union
• \enum: document an enumeration type
• \fn: document a fcuntion
• \var: document a variable, typedef, or enum value
• \def: document a #define
• \typedef: document a type definition
• \file: document a file
• \namespace: document a namespace
• \package: document a Java package
• \interface: document an IDL interface
3. Next, the contents of a special documentation block is parsed before being written to the HTML and / Latex output directories. This includes:
1. Special commands are executed.
2. Any white space and asterisks (*) are removed.
3. Blank lines are taken as new paragraphs.
4. Words are linked to their corresponding documentation. Where the word is preceded by a percent sign (%) the percent sign is removed and the word remains.
5. Where certain patterns are found in the text, links to members are created. Examples of this can be found on the automatic link generation page on the Doxygen documentation website.
6. When the documentation is for Latex, HTML tags are interpreted and converted to Latex equivalents. A list of supported HTML tags can be found on the HTML commands page on the Doxygen documentation website.

# Revision History

Revision History
Revision 1-15Fri Dec 02 2011
 Release for GA of Red Hat Enterprise Linux 6.2
Revision 1-8Mon Nov 14 2011
 BZ#753162, BZ#753159, BZ#753156, BZ#752135, BZ#752106 fixed typos and broken links
Revision 1-6Wed Nov 09 2011
 BZ#752135, BZ#752117, BZ#752105, BZ#752102: fix errors in code examples, replaced dead link
Revision 1-4Wed Nov 02 2011
 BZ#722512 Editing C/C++ Source Code section added.
Revision 1-1Wed Oct 26 2011
 BZ#722520 Eclipse section rearranged and empty chapters added ready to be filled
Revision 1-1Tue Sep 27 2011
 BZ#561718 minor edits
Revision 0-86Fri Sep 02 2011
 BZ#561718
Revision 0-83Tue Aug 30 2011
 BZ#561715
Revision 0-82Mon Aug 15 2011
 BZ#561716
Revision 0-81Thu Aug 04 2011
 BZ#642399
Revision 0-80Fri Jul 29 2011
 BZ#722516 Drop section 7.5
Revision 0-76Mon Jun 20 2011
 CVS section edited, compatibility sections returned BZ#653200, openssl compatibilities added to table BZ#642399
Revision 0-72Mon May 30 2011
 BZ#614289, CVS draft complete BZ#561716
Revision 0-71Tue May 24 2011
 BZ#614289
Revision 0-69Thu May 19 2011
 6.1 GA
Revision 0-68Thu May 19 2011
 BZ#5617325 final Publican edits
Revision 0-67Wed May 18 2011
 BZ#702561
Revision 0-66Tue May 17 2011
Revision 0-65Tue May 17 2011
 BZ#702388, BZ#703128, BZ#69357, BZ#561732 publican edits
Revision 0-60Mon May 16 2011
 BZ#614291, BZ#701986, BZ#702414
Revision 0-55Mon May 09 2011
 BZ#702417, BZ#701986, BZ#702414, BZ#702412, BZ#702396, BZ#702388
Revision 0-50Wed Apr 27 2011
Revision 0-45Mon Mar 28 2011
 BZ#702417, BZ#701986, BZ#702414, BZ#702412, BZ#702396, BZ#702388
Revision 0-41Fri Feb 04 2011
 BZ#561731: Doxygen content
Revision 0-40Tue Jan 25 2011
 BZ#642397: NSS Stack content
Revision 0-39Tue Dec 21 2010
 BZ#561732: Publican content
Revision 0-38Tue Dec 14 2010
 BZ#662822: Minor typo
Revision 0-37Tue Dec 07 2010
 Minor edits
Revision 0-36Thu Dec 02 2010
 Edited forked execution section
Revision 0-35Thu Dec 02 2010
 Edited documentation section
Revision 0-34Wed Dec 01 2010
 Rewrote ch-debugging.xml
Revision 0-33Mon Nov 29 2010
 Initialized
Revision 0-32Mon Nov 15 2010
 BZ#653200, removed content possibly inconsistent w/ stuff in App Compat Spec, to be re-added later
Revision 0-31Mon Nov 14 2010
 BZ#653200: adding backup copy of section containing compatibility content

## Index

### Symbols

.spec file
specfile Editor
compiling and building, Eclipse Built-in Specfile Editor

### A

GNU C Library
libraries and runtime support, GNU C Library Updates
Python pretty-printers
debugging, Python Pretty-Printers
KDE Development Framework
libraries and runtime support, KDE4 Architecture
architecture, KDE4
KDE Development Framework
libraries and runtime support, KDE4 Architecture
authorizing compile servers for connection
SSL and certificate management
SystemTap, Authorizing Compile Servers for Connection
automatic authorization
SSL and certificate management
SystemTap, Automatic Authorization
Autotools
compiling and building, Autotools

### B

backtrace
tools
GNU debugger, Simple GDB
Boost
libraries and runtime support, Boost
boost-doc
Boost
libraries and runtime support, Boost Documentation
breakpoint
fundamentals
GNU debugger, Simple GDB
breakpoints (conditional)
GNU debugger, Conditional Breakpoints
build integration
development toolkits
Eclipse, Development Toolkits
building
compiling and building, Compiling and Building

### C

C++ Standard Library, GNU
libraries and runtime support, The GNU C++ Standard Library
GNU C++ Standard Library
libraries and runtime support, GNU C++ Standard Library Updates
C/C++ Development Toolkit
development toolkits
Eclipse, Development Toolkits
cachegrind
tools
Valgrind, Valgrind Tools
callgrind
tools
Valgrind, Valgrind Tools
CDT
development toolkits
Eclipse, Development Toolkits
certificate management
SSL and certificate management
SystemTap, SSL and Certificate Management
checking functions (new)
GNU C Library
libraries and runtime support, GNU C Library Updates
Code Completion
libhover
libraries and runtime support, Setup and Usage
Command Group Availability Tab
integrated development environment
commands
fundamentals
GNU debugger, Simple GDB
profiling
Valgrind, Valgrind Tools
tools
Performance Counters for Linux (PCL) and perf, Perf Tool Commands
commonly-used commands
Autotools
compiling and building, Autotools
compatibility
libraries and runtime support, Compatibility
compile server
SystemTap, SystemTap Compile Server
compiling a C Hello World program
usage
GCC, Simple C Usage
compiling a C++ Hello World program
usage
GCC, Simple C++ Usage
compiling and building
Autotools, Autotools
commonly-used commands, Autotools
configuration script, Configuration Script
documentation, Autotools Documentation
plug-in for Eclipse, Autotools Plug-in for Eclipse
templates (supported), Autotools Plug-in for Eclipse
distributed compiling, Distributed Compiling
GNU Compiler Collection, GNU Compiler Collection (GCC)
documentation, GCC Documentation
required packages, Running GCC
usage, Running GCC
introduction, Compiling and Building
required packages, Distributed Compiling
specfile Editor, Eclipse Built-in Specfile Editor
plug-in for Eclipse, Eclipse Built-in Specfile Editor
conditional breakpoints
GNU debugger, Conditional Breakpoints
configuration script
Autotools
compiling and building, Configuration Script
configuring keyboard shortcuts
integrated development environment
connection authorization (compile servers)
SSL and certificate management
SystemTap, Authorizing Compile Servers for Connection
Console View
user interface
Eclipse, User Interface
Contents (Help Contents)
Help system
Eclipse, Help In Eclipse
continue
tools
GNU debugger, Simple GDB
integrated development environment

### D

debugfs file system
profiling
ftrace, ftrace
debugging
debuginfo-packages, Installing Debuginfo Packages
installation, Installing Debuginfo Packages
GNU debugger, GDB
fundamental mechanisms, GDB
GDB, GDB
requirements, GDB
introduction, Debugging
Python pretty-printers, Python Pretty-Printers
debugging output (formatted), Python Pretty-Printers
documentation, Python Pretty-Printers
pretty-printers, Python Pretty-Printers
variable tracking at assignments (VTA), Variable Tracking at Assignments
debugging a Hello World program
usage
GNU debugger, Running GDB
debugging output (formatted)
Python pretty-printers
debugging, Python Pretty-Printers
debuginfo-packages
debugging, Installing Debuginfo Packages
default
user interface
Eclipse, User Interface
development toolkits
Eclipse, Development Toolkits
distributed compiling
compiling and building, Distributed Compiling
documentation
Autotools
compiling and building, Autotools Documentation
Boost
libraries and runtime support, Boost Documentation
GNU C Library
libraries and runtime support, GNU C Library Documentation
GNU C++ Standard Library
libraries and runtime support, GNU C++ Standard Library Documentation
GNU Compiler Collection
compiling and building, GCC Documentation
GNU debugger, GDB Documentation
Java
libraries and runtime support, Java Documentation
KDE Development Framework
libraries and runtime support, kdelibs Documentation
OProfile
profiling, OProfile Documentation
Perl
libraries and runtime support, Perl Documentation
profiling
ftrace, ftrace Documentation
Python
libraries and runtime support, Python Documentation
Python pretty-printers
debugging, Python Pretty-Printers
Qt
libraries and runtime support, Qt Library Documentation
Ruby
libraries and runtime support, Ruby Documentation
SystemTap
profiling, SystemTap Documentation
Valgrind
profiling, Valgrind Documentation
DTK (development toolkits)
development toolkits
Eclipse, Development Toolkits
Dynamic Help
Help system
Eclipse, Help In Eclipse

### E

Eclipse
development toolkits, Development Toolkits
build integration, Development Toolkits
C/C++ Development Toolkit, Development Toolkits
CDT, Development Toolkits
DTK (development toolkits), Development Toolkits
hot patch, Development Toolkits
Java Development Toolkit, Development Toolkits
JDT, Development Toolkits
Help system, Help In Eclipse
Contents (Help Contents), Help In Eclipse
Dynamic Help, Help In Eclipse
Workbench User Guide, Help In Eclipse
integrated development environment, The Eclipse Integrated Development Environment (IDE)
Command Group Availability Tab, The quick access menu
configuring keyboard shortcuts, The quick access menu
IDE (integrated development environment), The Eclipse Integrated Development Environment (IDE)
perspectives, The Eclipse Integrated Development Environment (IDE)
Shortcuts Tab, The quick access menu
Tool Bar Visibility, The quick access menu
useful hints, Useful Hints
user interface, User Interface
workbench, The Eclipse Integrated Development Environment (IDE)
introduction, Introduction to Eclipse
libhover
libraries and runtime support, libhover Plug-in
profiling, Profiling In Eclipse
projects, Understanding Eclipse Projects
New Project Wizard, Understanding Eclipse Projects
technical overview, Understanding Eclipse Projects
workspace (overview), Understanding Eclipse Projects
Workspace Launcher, Understanding Eclipse Projects
user interface
Console View, User Interface
default, User Interface
Editor, User Interface
Outline Window, User Interface
Problems View, User Interface
Project Explorer, User Interface
quick fix (Problems View), User Interface
Editor
user interface
Eclipse, User Interface
execution (forked)
GNU debugger, Forked Execution

### F

feedback
contact information for this manual, We Need Feedback!
finish
tools
GNU debugger, Simple GDB
forked execution
GNU debugger, Forked Execution
formatted debugging output
Python pretty-printers
debugging, Python Pretty-Printers
framework (ftrace)
profiling
ftrace, ftrace
ftrace
profiling, ftrace
debugfs file system, ftrace
documentation, ftrace Documentation
framework (ftrace), ftrace
usage, Using ftrace
function tracer
profiling
ftrace, ftrace
fundamental commands
fundamentals
GNU debugger, Simple GDB
fundamental mechanisms
GNU debugger
debugging, GDB
fundamentals
GNU debugger, Simple GDB

### G

gcc
GNU Compiler Collection
compiling and building, GNU Compiler Collection (GCC)
GCC C
usage
compiling a C Hello World program, Simple C Usage
GCC C++
usage
compiling a C++ Hello World program, Simple C++ Usage
GDB
GNU debugger
debugging, GDB
glibc
libraries and runtime support, The GNU C Library
GNU C Library
libraries and runtime support, The GNU C Library
GNU C++ Standard Library
libraries and runtime support, The GNU C++ Standard Library
GNU Compiler Collection
compiling and building, GNU Compiler Collection (GCC)
GNU debugger
conditional breakpoints, Conditional Breakpoints
debugging, GDB
documentation, GDB Documentation
execution (forked), Forked Execution
forked execution, Forked Execution
fundamentals, Simple GDB
breakpoint, Simple GDB
commands, Simple GDB
halting an executable, Simple GDB
inspecting the state of an executable, Simple GDB
starting an executable, Simple GDB
interfaces (CLI and machine), Alternative User Interfaces for GDB
tools, Simple GDB
backtrace, Simple GDB
continue, Simple GDB
finish, Simple GDB
help, Simple GDB
list, Simple GDB
next, Simple GDB
print, Simple GDB
quit, Simple GDB
step, Simple GDB
usage, Running GDB
debugging a Hello World program, Running GDB
variations and environments, Alternative User Interfaces for GDB

### H

halting an executable
fundamentals
GNU debugger, Simple GDB
GNU C Library
libraries and runtime support, The GNU C Library
helgrind
tools
Valgrind, Valgrind Tools
help
getting help, Do You Need Help?
tools
GNU debugger, Simple GDB
Help system
Eclipse, Help In Eclipse
hints
integrated development environment
Eclipse, Useful Hints
host (compile server host)
compile server
SystemTap, SystemTap Compile Server
hot patch
development toolkits
Eclipse, Development Toolkits
Hover Help
libhover
libraries and runtime support, Setup and Usage

### I

IDE (integrated development environment)
integrated development environment
Eclipse, The Eclipse Integrated Development Environment (IDE)
indexing
libhover
libraries and runtime support, libhover Plug-in
inspecting the state of an executable
fundamentals
GNU debugger, Simple GDB
installation
debuginfo-packages
debugging, Installing Debuginfo Packages
integrated development environment
Eclipse, The Eclipse Integrated Development Environment (IDE)
GNU C Library
libraries and runtime support, GNU C Library Updates
interfaces (CLI and machine)
GNU debugger, Alternative User Interfaces for GDB
introduction
compiling and building, Compiling and Building
debugging, Debugging
Eclipse, Introduction to Eclipse
libraries and runtime support, Libraries and Runtime Support
profiling, Profiling
SystemTap, SystemTap
ISO 14482 Standard C++ library
GNU C++ Standard Library
libraries and runtime support, The GNU C++ Standard Library
ISO C++ TR1 elements, added support for
GNU C++ Standard Library
libraries and runtime support, GNU C++ Standard Library Updates

### J

Java
libraries and runtime support, Java
Java Development Toolkit
development toolkits
Eclipse, Development Toolkits
JDT
development toolkits
Eclipse, Development Toolkits

### K

KDE Development Framework
libraries and runtime support, KDE Development Framework
KDE4 architecture
KDE Development Framework
libraries and runtime support, KDE4 Architecture
kdelibs-devel
KDE Development Framework
libraries and runtime support, KDE Development Framework
kernel information packages
profiling
SystemTap, SystemTap
integrated development environment
KHTML
KDE Development Framework
libraries and runtime support, KDE4 Architecture
KIO
KDE Development Framework
libraries and runtime support, KDE4 Architecture
KJS
KDE Development Framework
libraries and runtime support, KDE4 Architecture
KNewStuff2
KDE Development Framework
libraries and runtime support, KDE4 Architecture
KXMLGUI
KDE Development Framework
libraries and runtime support, KDE4 Architecture

### L

libhover
libraries and runtime support, libhover Plug-in
libraries
runtime support, Libraries and Runtime Support
libraries and runtime support
Boost, Boost
boost-doc, Boost Documentation
documentation, Boost Documentation
message passing interface (MPI), Boost
meta-package, Boost
MPICH2, Boost
Open MPI, Boost
sub-packages, Boost
C++ Standard Library, GNU, The GNU C++ Standard Library
compatibility, Compatibility
glibc, The GNU C Library
GNU C Library, The GNU C Library
checking functions (new), GNU C Library Updates
documentation, GNU C Library Documentation
header files, The GNU C Library
GNU C++ Standard Library, The GNU C++ Standard Library
documentation, GNU C++ Standard Library Documentation
ISO 14482 Standard C++ library, The GNU C++ Standard Library
ISO C++ TR1 elements, added support for, GNU C++ Standard Library Updates
libstdc++-devel, The GNU C++ Standard Library
libstdc++-docs, GNU C++ Standard Library Documentation
Standard Template Library, The GNU C++ Standard Library
introduction, Libraries and Runtime Support
Java, Java
documentation, Java Documentation
KDE Development Framework, KDE Development Framework
documentation, kdelibs Documentation
KDE4 architecture, KDE4 Architecture
kdelibs-devel, KDE Development Framework
KHTML, KDE4 Architecture
KIO, KDE4 Architecture
KJS, KDE4 Architecture
KNewStuff2, KDE4 Architecture
KXMLGUI, KDE4 Architecture
Phonon, KDE4 Architecture
Plasma, KDE4 Architecture
Solid, KDE4 Architecture
Sonnet, KDE4 Architecture
Strigi, KDE4 Architecture
Telepathy, KDE4 Architecture
libhover, libhover Plug-in
Code Completion, Setup and Usage
Eclipse, libhover Plug-in
Hover Help, Setup and Usage
indexing, libhover Plug-in
usage, Setup and Usage
libstdc++, The GNU C++ Standard Library
Perl, Perl
documentation, Perl Documentation
module installation, Installation
Python, Python
documentation, Python Documentation
Qt, Qt
documentation, Qt Library Documentation
meta object compiler (MOC), Qt
Qt Creator, Qt Creator
qt-doc, Qt Library Documentation
widget toolkit, Qt
Ruby, Ruby
documentation, Ruby Documentation
ruby-devel, Ruby
libstdc++
libraries and runtime support, The GNU C++ Standard Library
libstdc++-devel
GNU C++ Standard Library
libraries and runtime support, The GNU C++ Standard Library
libstdc++-docs
GNU C++ Standard Library
libraries and runtime support, GNU C++ Standard Library Documentation
GNU C Library
libraries and runtime support, GNU C Library Updates
list
tools
GNU debugger, Simple GDB
Performance Counters for Linux (PCL) and perf, Perf Tool Commands
GNU C Library
libraries and runtime support, GNU C Library Updates

### M

machine interface
GNU debugger, Alternative User Interfaces for GDB
massif
tools
Valgrind, Valgrind Tools
mechanisms
GNU debugger
debugging, GDB
memcheck
tools
Valgrind, Valgrind Tools
Help system
Eclipse, Help In Eclipse
integrated development environment
Eclipse, The Eclipse Integrated Development Environment (IDE)
integrated development environment
message passing interface (MPI)
Boost
libraries and runtime support, Boost
meta object compiler (MOC)
Qt
libraries and runtime support, Qt
meta-package
Boost
libraries and runtime support, Boost
module installation
Perl
libraries and runtime support, Installation
module signing (compile server authorization)
SSL and certificate management
SystemTap, Authorizing Compile Servers for Module Signing (for Unprivileged Users)
MPICH2
Boost
libraries and runtime support, Boost

### N

new extensions
GNU C++ Standard Library
libraries and runtime support, GNU C++ Standard Library Updates
new libraries
Boost
libraries and runtime support, Boost Updates
New Project Wizard
projects
Eclipse, Understanding Eclipse Projects
next
tools
GNU debugger, Simple GDB

### O

opannotate
tools
OProfile, OProfile Tools
oparchive
tools
OProfile, OProfile Tools
opcontrol
tools
OProfile, OProfile Tools
Open MPI
Boost
libraries and runtime support, Boost
opgprof
tools
OProfile, OProfile Tools
opreport
tools
OProfile, OProfile Tools
OProfile
profiling, OProfile
documentation, OProfile Documentation
usage, Using OProfile
tools, OProfile Tools
opannotate, OProfile Tools
oparchive, OProfile Tools
opcontrol, OProfile Tools
opgprof, OProfile Tools
opreport, OProfile Tools
oprofiled
OProfile
profiling, OProfile
Outline Window
user interface
Eclipse, User Interface

### P

perf
profiling
Performance Counters for Linux (PCL) and perf, Performance Counters for Linux (PCL) Tools and perf
usage
Performance Counters for Linux (PCL) and perf, Using Perf
Performance Counters for Linux (PCL) and perf
profiling, Performance Counters for Linux (PCL) Tools and perf
subsystem (PCL), Performance Counters for Linux (PCL) Tools and perf
tools, Perf Tool Commands
commands, Perf Tool Commands
list, Perf Tool Commands
record, Perf Tool Commands
report, Perf Tool Commands
stat, Perf Tool Commands
usage, Using Perf
perf, Using Perf
Perl
libraries and runtime support, Perl
perspectives
integrated development environment
Eclipse, The Eclipse Integrated Development Environment (IDE)
Phonon
KDE Development Framework
libraries and runtime support, KDE4 Architecture
Plasma
KDE Development Framework
libraries and runtime support, KDE4 Architecture
plug-in for Eclipse
Autotools
compiling and building, Autotools Plug-in for Eclipse
profiling
Valgrind, Valgrind Plug-in for Eclipse
specfile Editor
compiling and building, Eclipse Built-in Specfile Editor
pretty-printers
Python pretty-printers
debugging, Python Pretty-Printers
print
tools
GNU debugger, Simple GDB
Problems View
user interface
Eclipse, User Interface
Profile As
Eclipse
profiling, Profiling In Eclipse
Eclipse
profiling, Profiling In Eclipse
profiling
Eclipse, Profiling In Eclipse
Profile As, Profiling In Eclipse
Profile Configuration Menu, Profiling In Eclipse
ftrace, ftrace
introduction, Profiling
OProfile, OProfile
oprofiled, OProfile
Performance Counters for Linux (PCL) and perf, Performance Counters for Linux (PCL) Tools and perf
SystemTap, SystemTap
Valgrind, Valgrind
Project Explorer
user interface
Eclipse, User Interface
projects
Eclipse, Understanding Eclipse Projects
Python
libraries and runtime support, Python
Python pretty-printers
debugging, Python Pretty-Printers

### Q

Qt
libraries and runtime support, Qt
Qt Creator
Qt
libraries and runtime support, Qt Creator
qt-doc
Qt
libraries and runtime support, Qt Library Documentation
integrated development environment
quick fix (Problems View)
user interface
Eclipse, User Interface
quit
tools
GNU debugger, Simple GDB

### R

record
tools
Performance Counters for Linux (PCL) and perf, Perf Tool Commands
report
tools
Performance Counters for Linux (PCL) and perf, Perf Tool Commands
required packages
compiling and building, Distributed Compiling
GNU Compiler Collection
compiling and building, Running GCC
profiling
SystemTap, SystemTap
requirements
GNU debugger
debugging, GDB
Ruby
libraries and runtime support, Ruby
ruby-devel
Ruby
libraries and runtime support, Ruby
runtime support
libraries, Libraries and Runtime Support

### S

scripts (SystemTap scripts)
profiling
SystemTap, SystemTap
setup
libhover
libraries and runtime support, Setup and Usage
Shortcuts Tab
integrated development environment
signed modules
SSL and certificate management
SystemTap, Authorizing Compile Servers for Module Signing (for Unprivileged Users)
unprivileged user support
SystemTap, SystemTap Support for Unprivileged Users
Solid
KDE Development Framework
libraries and runtime support, KDE4 Architecture
Sonnet
KDE Development Framework
libraries and runtime support, KDE4 Architecture
specfile Editor
compiling and building, Eclipse Built-in Specfile Editor
SSL and certificate management
SystemTap, SSL and Certificate Management
Standard Template Library
GNU C++ Standard Library
libraries and runtime support, The GNU C++ Standard Library
starting an executable
fundamentals
GNU debugger, Simple GDB
stat
tools
Performance Counters for Linux (PCL) and perf, Perf Tool Commands
step
tools
GNU debugger, Simple GDB
Strigi
KDE Development Framework
libraries and runtime support, KDE4 Architecture
sub-packages
Boost
libraries and runtime support, Boost
subsystem (PCL)
profiling
Performance Counters for Linux (PCL) and perf, Performance Counters for Linux (PCL) Tools and perf
supported templates
Autotools
compiling and building, Autotools Plug-in for Eclipse
SystemTap
compile server, SystemTap Compile Server
host (compile server host), SystemTap Compile Server
profiling, SystemTap
documentation, SystemTap Documentation
introduction, SystemTap
kernel information packages, SystemTap
required packages, SystemTap
scripts (SystemTap scripts), SystemTap
SSL and certificate management, SSL and Certificate Management
automatic authorization, Automatic Authorization
connection authorization (compile servers), Authorizing Compile Servers for Connection
module signing (compile server authorization), Authorizing Compile Servers for Module Signing (for Unprivileged Users)
unprivileged user support, SystemTap Support for Unprivileged Users
signed modules, SystemTap Support for Unprivileged Users

### T

user interface
Eclipse, User Interface
user interface
Eclipse, User Interface
technical overview
projects
Eclipse, Understanding Eclipse Projects
Telepathy
KDE Development Framework
libraries and runtime support, KDE4 Architecture
templates (supported)
Autotools
compiling and building, Autotools Plug-in for Eclipse
Tool Bar Visibility
integrated development environment
tools
GNU debugger, Simple GDB
OProfile, OProfile Tools
Performance Counters for Linux (PCL) and perf, Perf Tool Commands
profiling
Valgrind, Valgrind Tools
Valgrind, Valgrind Tools
user interface
Eclipse, User Interface

### U

unprivileged user support
SystemTap, SystemTap Support for Unprivileged Users
unprivileged users
unprivileged user support
SystemTap, SystemTap Support for Unprivileged Users
Boost
libraries and runtime support, Boost Updates
GNU C Library
libraries and runtime support, GNU C Library Updates
GNU C++ Standard Library
libraries and runtime support, GNU C++ Standard Library Updates
Perl
libraries and runtime support, Perl Updates
Python
libraries and runtime support, Python Updates
Qt
libraries and runtime support, Qt Updates
usage
GNU Compiler Collection
compiling and building, Running GCC
GNU debugger, Running GDB
fundamentals, Simple GDB
libhover
libraries and runtime support, Setup and Usage
Performance Counters for Linux (PCL) and perf, Using Perf
profiling
ftrace, Using ftrace
OProfile, Using OProfile
Valgrind
profiling, Using Valgrind
useful hints
integrated development environment
Eclipse, Useful Hints
user interface
integrated development environment
Eclipse, User Interface

### V

Valgrind
profiling, Valgrind
commands, Valgrind Tools
documentation, Valgrind Documentation
plug-in for Eclipse, Valgrind Plug-in for Eclipse
tools, Valgrind Tools
usage, Using Valgrind
tools
cachegrind, Valgrind Tools
callgrind, Valgrind Tools
helgrind, Valgrind Tools
massif, Valgrind Tools
memcheck, Valgrind Tools
variable tracking at assignments (VTA)
debugging, Variable Tracking at Assignments
variations and environments
GNU debugger, Alternative User Interfaces for GDB
user interface
Eclipse, User Interface

### W

widget toolkit
Qt
libraries and runtime support, Qt
workbench
integrated development environment
Eclipse, The Eclipse Integrated Development Environment (IDE)
Workbench User Guide
Help system
Eclipse, Help In Eclipse
workspace (overview)
projects
Eclipse, Understanding Eclipse Projects
Workspace Launcher
projects
Eclipse, Understanding Eclipse Projects