// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \page linux.html
    \title Qt for Linux/X11
    \brief Platform support for Linux/X11.
    \ingroup supportedplatform

    Qt's support for different Linux platforms is extensive and mature.

    To download and install Qt for Linux, follow the instructions on the
    \l{Getting Started with Qt} page.

    \target linux-supported-configurations
    \section1 Supported Configurations

    The following configurations are supported.

    \include supported-platforms.qdocinc linux

    \section1 Requirements for Development Host

    The Qt installers for Linux assume that a C++ compiler, debugger,
    make, and other development tools are provided by the host
    operating system. In addition, building graphical Qt applications
    requires OpenGL libraries and headers installed. Most Linux
    distributions do not install all of these by default, but setting
    up a development environment is still straightforward.

    Use the following commands to install the basic requirements for
    building Qt applications:

    \section3 Debian/Ubuntu (apt-get)

    \badcode
    sudo apt-get install build-essential libgl1-mesa-dev
    \endcode

    \section3 Fedora/RHEL/CentOS (yum)

    \badcode
    sudo yum groupinstall "C Development Tools and Libraries"
    sudo yum install mesa-libGL-devel
    \endcode

    \section3 openSUSE (zypper)

    \badcode
    sudo zypper install -t pattern devel_basis
    \endcode

    \section1 Building Qt from Source

    You can also build Qt from the source package and configure it according
    to your target platform. The source packages are obtained from
    \l{http://www.qt.io/download/}.

    Below, you will find more information about building Qt from source.
    \list
    \li \l {Qt for X11 Requirements}
    \li \l{Qt for Linux/X11 - Building from Source}
    \endlist

    \section1 Deployment and Other Issues

    The pages below covers specific issues and recommendations for creating
    Linux/X11 applications.

    \list
    \li \l{Qt for Linux/X11 - Deployment}
    \li \l{Qt for Linux/X11 - Specific Issues}
    \endlist

    \section1 Where to Go from Here

    We invite you to explore the rest of Qt. We prepared overviews which help
    you decide which APIs to use and our examples demonstrate how to use our
    API.

    \list
    \li \l{Qt Overviews} - list of topics about application development
    \li \l{Qt Examples and Tutorials}{Examples and Tutorials} - code samples and tutorials
    \li \l{Qt Reference Pages} - a listing of C++ and QML APIs
    \endlist

    Qt's vibrant and active community site, \l{http://qt.io} houses
    a wiki, a forum, and additional learning guides and presentations.
*/

/*!
    \page linux-requirements.html
    \title Qt for X11 Requirements
    \brief Setting up the X11 environment for Qt.

    \section1 Platform Plugin Dependencies

    On Linux, the \e xcb QPA (Qt Platform Abstraction) platform plugin is used.
    It provides the basic functionality needed by \l{Qt GUI} and \l{Qt Widgets}
    to run against X11. Its library dependencies are described the following
    table. To build Qt from its source code, you will also need to install the
    development packages for these libraries for your system.

    \table 100%
    \header
    \li Name
    \li Library
    \li Notes
    \li Configuration options
    \li Minimum working version
    \row {id="OptionalColor"}
    \li XRender
    \li libXrender
    \li X Rendering Extension; used for anti-aliasing and alpha cursor support
    \li \tt{-xrender} or auto-detected
    \li 0.9.0
    \row {id="OptionalColor"}
    \li xcb-render
    \li libxcb-render
    \li X C Bindings for Render extension
    \li auto-detected
    \li 1.11
    \row {id="OptionalColor"}
    \li xcb-render-util
    \li libxcb-render-util
    \li Utility library for XCB for Render extension
    \li auto-detected
    \li 0.3.9
    \row {id="OptionalColor"}
    \li xcb-shape
    \li libxcb-shape
    \li X C Bindings for Shape extension
    \li auto-detected
    \li 1.11
    \row {id="DefaultColor"}
    \li xcb-randr
    \li libxcb-randr
    \li X C Bindings for Resize and Rotate Extension
    \li auto-detected
    \li 1.11
    \row {id="DefaultColor"}
    \li xcb-xfixes
    \li libxcb-xfixes
    \li X C Bindings for Fixes Extension
    \li auto-detected
    \li 1.11
    \row {id="DefaultColor"}
    \li xcb-xkb
    \li libxcb-xkb
    \li X C Bindings for XKeyboard Extension
    \li auto-detected
    \li 1.11
    \row {id="DefaultColor"}
    \li xcb-sync
    \li libxcb-sync
    \li X C Bindings for Sync Extension
    \li auto-detected
    \li 1.11
    \row {id="DefaultColor"}
    \li xcb-shm
    \li libxcb-shm
    \li X C Bindings for Shared Memory Extension
    \li auto-detected
    \li 1.11
    \row {id="DefaultColor"}
    \li xcb-icccm
    \li libxcb-icccm
    \li X C Bindings for ICCCM Protocol
    \li auto-detected
    \li 0.3.9
    \row {id="DefaultColor"}
    \li xcb-keysyms
    \li libxcb-keysyms
    \li Utility library for XCB for keycode conversion
    \li auto-detected
    \li 0.3.9
    \row {id="DefaultColor"}
    \li xcb-image
    \li libxcb-image
    \li Utility library for XCB for XImage and XShmImage, used for QBackingStore and cursor support
    \li auto-detected
    \li 0.3.9
    \row {id="DefaultColor"}
    \li xcb-util
    \li libxcb-util
    \li Utility library for XCB for atom, aux and event
    \li auto-detected
    \li 0.3.9

    \row {id="OptionalColor"}
    \li xkbcommon
    \li libxkbcommon
    \li Keymap handling
    \li \tt{-xkbcommon} or auto-detected
    \li 0.5.0
    \row {id="OptionalColor"}
    \li xkbcommon-x11
    \li libxkbcommon-x11
    \li Keymap handling
    \li auto-detected
    \li 0.5.0

    \row {id="OptionalColor"}
    \li Fontconfig
    \li libfontconfig
    \li Font customization and configuration
    \li \tt{-fontconfig} or auto-detected
    \li 2.6
    \row {id="OptionalColor"}
    \li FreeType
    \li libfreetype
    \li Font engine
    \li
    \li 2.3.0
    \row {id="DefaultColor"}
    \li Xext
    \li libXext
    \li X Extensions
    \li
    \li 6.4.3
    \row {id="DefaultColor"}
    \li X11
    \li libX11
    \li X11 client-side library
    \li
    \li 6.2.1
    \row {id="DefaultColor"}
    \li xcb
    \li libxcb
    \li X C Binding library
    \li
    \li 1.11
    \row {id="DefaultColor"}
    \li X11-xcb
    \li libX11-xcb
    \li Xlib/XCB interface library
    \li
    \li 1.3.2

    \row {id="SMColor"}
    \li SM
    \li libSM
    \li X Session Management
    \li \tt{-sm} or auto-detected
    \li 6.0.4
    \row {id="SMColor"}
    \li ICE
    \li libICE
    \li Inter-Client Exchange
    \li \tt{-sm} or auto-detected
    \li 6.3.5

    \row {id="GlibColor"}
    \li glib
    \li libglib-2.0
    \li Common event loop handling
    \li \tt{-glib} or auto-detected
    \li 2.8.3
    \row {id="PthreadColor"}
    \li pthread
    \li libpthread
    \li Multithreading
    \li
    \li 2.3.5
    \endtable

    Development packages for these libraries contain header files that are used
    when building Qt from its source code. On Debian-based GNU/Linux systems,
    for example, we recommend that you install the following development
    packages:

    \list
    \li libfontconfig1-dev
    \li libfreetype6-dev
    \li libx11-dev
    \li libx11-xcb-dev
    \li libxext-dev
    \li libxfixes-dev
    \li libxi-dev
    \li libxrender-dev
    \li libxcb1-dev
    \li libxcb-glx0-dev
    \li libxcb-keysyms1-dev
    \li libxcb-image0-dev
    \li libxcb-shm0-dev
    \li libxcb-icccm4-dev
    \li libxcb-sync-dev
    \li libxcb-xfixes0-dev
    \li libxcb-shape0-dev
    \li libxcb-randr0-dev
    \li libxcb-render-util0-dev
    \li libxcb-util-dev
    \li libxcb-xinerama0-dev
    \li libxcb-xkb-dev
    \li libxkbcommon-dev
    \li libxkbcommon-x11-dev
    \endlist

    Some of these packages depend on others in this list, so installing one
    may cause others to be automatically installed. Other distributions may
    provide system packages with similar names.

    \section1 Accessibility Dependencies

    The Qt accessibility implementation uses the \e{Assistive Technology
    Service Provider Interface} (AT-SPI). Besides DBUS, the development
    package \c{libatspi2.0-dev} must be installed.

    \section1 OpenGL Dependencies

    Configure attempts to automatically detect OpenGL ES 2.0, or later, or
    regular desktop OpenGL. You can disable OpenGL support by using the
    \c -no-opengl option.

    \note The Qt OpenGL module (which contains classes that start with \e QGL)
    has been deprecated in favor of the \l{Qt GUI} module (which contains
    classes that start with \e QOpenGL).

    \omit
    \section1 Speech Dependencies

    \l{Qt Speech} depends on Speech Dispatcher (libspeechd) on the Linux platform.
    The following development packages should be installed:

    \list
    \li flite1-dev
    \li libspeechd-dev
    \li speech-dispatcher
    \endlist
    \endomit

    \section1 QDoc Dependencies
    \l{QDoc Manual}{QDoc} uses Clang to parse C++ code.
    If you wish to build QDoc manually, refer to \l {Installing Clang for QDoc}
    for specific build requirements.
*/

/*!
    \page linux-building.html
    \title Qt for Linux/X11 - Building from Source
    \brief How to configure and build Qt on Linux/X11 platforms.

    You can download the Qt sources from the \l Downloads page. For more
    information, visit the \l{Getting Started with Qt} page.

    Qt for X11 has some requirements that are given in more detail
    in the \l{Qt for X11 Requirements} document.

    Distribution packagers can find information how to package Qt in the
    \l{Qt Packaging Recommendations}{packaging recommendations}.

    \section1 Step 1: Unpacking the Archive
        Unpack the archive if you have not done so already. For example,
        if you have the \c{qt-everywhere-src-%VERSION%.tar.gz}
        package, type the following commands at a command line prompt:

    \snippet snippets/code/doc_src_installation.qdoc 0

        This creates the directory \c{/tmp/qt-everywhere-src-%VERSION%}
        containing the files from the archive. We only support the GNU version of
        the tar archiving utility. Note that on some systems it is called gtar.

    \section1 Step 2: Build the Qt Library

        To configure the Qt library for your machine type, run the
        \c{./configure} script in the package directory.

        By default, Qt is configured for installation in the
        \c{/usr/local/Qt-%VERSION%} directory, but this can be
        changed by using the \c{-prefix} option.

        The \l{Qt Configure Options}{Configure Options} page contains more
        information about the configure options.

    \snippet snippets/code/doc_src_installation.qdoc 1

        The \l{Qt Configure Options}{Configure Options} page contains more
        information about the configure options.

        To create the library and compile all the examples, tools,
        and tutorials, type:

    \snippet snippets/code/doc_src_installation.qdoc 2

        If \c{-prefix} is outside the build directory, you need to install
        the library, examples, tools, and tutorials in the appropriate
        place. To do this (as root if necessary), type:

    \snippet snippets/code/doc_src_installation.qdoc 3

        Note that on some systems the make utility is named differently, like gmake.
        The configure script tells you which make utility to use.

        \note Later, if you need to reconfigure and rebuild Qt from the same location,
        ensure that all traces of the previous configuration are removed. To do so, from
        the build directory, type \c{make confclean} before running \c configure again.

    \section1 Step 3: Set the Environment Variables

        To use Qt, some environment variables need to be extended.

    \snippet snippets/code/doc_src_installation.qdoc 4

        This is done as follows:

        In \c{.profile} (if your shell is bash, ksh, zsh or sh), add the
        following lines:

    \snippet snippets/code/doc_src_installation.qdoc 5

        In \c{.login} (if your shell is csh or tcsh), add the following line:

    \snippet snippets/code/doc_src_installation.qdoc 6

        If you use a different shell, modify your environment variables accordingly.

        For compilers that do not support rpath you must also extend the
        \c LD_LIBRARY_PATH environment variable to include
        \c{/usr/local/Qt-%VERSION%/lib}. On Linux with GCC this step
        is not needed.

*/

/*!
    \page linux-deployment.html
    \title Qt for Linux/X11 - Deployment

    This documentation discusses specific deployment issues for \l{Qt for
    Linux/X11}. We will demonstrate the procedures in terms of deploying the
    \l{tools/plugandpaint/app}{Plug & Paint} application that is provided in Qt's
    examples directory.

    Due to the proliferation of Unix systems (such as commercial Unixes, Linux
    distributions, and so on), deployment on Unix is a complex
    topic. Before we start, be aware that programs compiled for one
    Unix flavor will probably not run on a different Unix system. For
    example, unless you use a cross-compiler, you cannot compile your
    application on Irix and distribute it on AIX.

    \section1 Static Linking

    Static linking is often the safest and easiest way to distribute
    an application on Unix since it relieves you from the task of
    distributing the Qt libraries and ensuring that they are located
    in the default search path for libraries on the target system.

    \section2 Building Qt Statically

    To use this approach, you must start by installing a static version
    of the Qt library:

    \snippet snippets/code/doc_src_deployment.qdoc 0

    We specify the prefix so that we do not overwrite the existing Qt
    installation. The example above only builds the Qt libraries,
    i.e. the examples and Qt Designer will not be built.  When \c make
    is done, you will find the Qt libraries in the \c /path/to/Qt/lib
    directory.

    When linking your application against static Qt libraries, note
    that you might need to add more libraries to the \c LIBS line in
    your project file. For more information, see the \l {Application
    Dependencies} section.

    \section2 Linking the Application to the Static Version of Qt

    Once Qt is built statically, the next step is to regenerate the
    makefile and rebuild the application. First, we must go into the
    directory that contains the application:

    \snippet snippets/code/doc_src_deployment.qdoc 1

    Now run qmake to create a new makefile for the application, and do
    a clean build to create the statically linked executable:

    \snippet snippets/code/doc_src_deployment.qdoc 2

    You probably want to link against the release libraries, and you
    can specify this when invoking \c qmake. Note that we must set the
    path to the static Qt that we just built.

    To check that the application really links statically with Qt, run
    the \c ldd tool (available on most Unices):

    \snippet snippets/code/doc_src_deployment.qdoc 3

    Verify that the Qt libraries are not mentioned in the output.

    Now, provided that everything compiled and linked without any
    errors, we should have a \c plugandpaint file that is ready for
    deployment. One easy way to check that the application really can
    be run stand-alone is to copy it to a machine that doesn't have Qt
    or any Qt applications installed, and run it on that machine.

    Remember that if your application depends on compiler specific
    libraries, these must still be redistributed along with your
    application. For more information, see the \l {Application
    Dependencies} section.

    The \l {tools/plugandpaint/app}{Plug & Paint} example consists of
    several components: The core application (\l
    {tools/plugandpaint/app}{Plug & Paint}), and the \l
    {tools/plugandpaint/plugins/basictools}{Basic Tools} and \l
    {tools/plugandpaint/plugins/extrafilters}{Extra Filters}
    plugins. Since we cannot deploy plugins using the static linking
    approach, the executable we have prepared so far is
    incomplete. The application will run, but the functionality will
    be disabled due to the missing plugins. To deploy plugin-based
    applications we should use the shared library approach.

    \section1 Shared Libraries

    We have two challenges when deploying the \l
    {tools/plugandpaint/app}{Plug & Paint} application using the shared
    libraries approach: The Qt runtime has to be correctly
    redistributed along with the application executable, and the
    plugins have to be installed in the correct location on the target
    system so that the application can find them.

    \section2 Building Qt as a Shared Library

    We assume that you already have installed Qt as a shared library,
    which is the default when installing Qt, in the \c /path/to/Qt
    directory.

    \section2 Linking the Application to Qt as a Shared Library

    After ensuring that Qt is built as a shared library, we can build
    the \l {tools/plugandpaint/app}{Plug & Paint} application. First, we
    must go into the directory that contains the application:

    \snippet snippets/code/doc_src_deployment.qdoc 4

    Now run qmake to create a new makefile for the application, and do
    a clean build to create the dynamically linked executable:

    \snippet snippets/code/doc_src_deployment.qdoc 5

    This builds the core application, the following will build the
    plugins:

    \snippet snippets/code/doc_src_deployment.qdoc 6

    If everything compiled and linked without any errors, we will get
    a \c plugandpaint executable and the \c libpnp_basictools.so and
    \c libpnp_extrafilters.so plugin files.

    \section2 Creating the Application Package

    There is no standard package management on Unix, so the method we
    present below is a generic solution. See the documentation for
    your target system for information on how to create a package.

    To deploy the application, we must make sure that we copy the
    relevant Qt libraries (corresponding to the Qt modules used in the
    application), the \l {Qt Plugins}{platform plugin}, and the executable
    to the same directory tree. Remember that if your application depends
    on compiler specific libraries, these must also be redistributed along
    with your application. For more information, see the \l {Application
    Dependencies} section.

    We'll cover the plugins shortly, but the main issue with shared
    libraries is that you must ensure that the dynamic linker will
    find the Qt libraries. Unless told otherwise, the dynamic linker
    doesn't search the directory where your application resides. There
    are many ways to solve this:

    \list

    \li You can install the Qt libraries in one of the system
       library paths (e.g. \c /usr/lib on most systems).

    \li You can pass a predetermined path to the \c -rpath command-line
       option when linking the application. This will tell the dynamic
       linker to look in this directory when starting your application.

    \li You can write a startup script for your application, where you
       modify the dynamic linker configuration (e.g., adding your
       application's directory to the \c LD_LIBRARY_PATH environment
       variable. \note If your application will be running with "Set
       user ID on execution," and if it will be owned by root, then
       LD_LIBRARY_PATH will be ignored on some platforms. In this
       case, use of the LD_LIBRARY_PATH approach is not an option).

    \endlist

    The disadvantage of the first approach is that the user must have
    super user privileges. The disadvantage of the second approach is
    that the user may not have privileges to install into the
    predetermined path. In either case, the users don't have the option
    of installing to their home directory. We recommend using the
    third approach since it is the most flexible. For example, a \c
    plugandpaint.sh script will look like this:

    \snippet snippets/code/doc_src_deployment.qdoc 7

    By running this script instead of the executable, you are sure
    that the Qt libraries will be found by the dynamic linker. Note
    that you only have to rename the script to use it with other
    applications.

    When looking for plugins, the application searches in a plugins
    subdirectory inside the directory of the application
    executable. Either you have to manually copy the plugins into the
    \c plugins directory, or you can set the \c DESTDIR in the
    plugins' project files:

    \snippet snippets/code/doc_src_deployment.pro 8

    An archive distributing all the Qt libraries, and all the plugins,
    required to run the \l {tools/plugandpaint/app}{Plug & Paint}
    application, would have to include the following files:

    \table 100%
    \header
        \li Component \li {2, 1} File Name
    \row
        \li The executable
        \li {2, 1} \c plugandpaint
    \row
        \li The script to run the executable
        \li {2, 1} \c plugandpaint.sh
    \row
        \li The Basic Tools plugin
        \li {2, 1} \c plugins\libpnp_basictools.so
    \row
        \li The ExtraFilters plugin
        \li {2, 1} \c plugins\libpnp_extrafilters.so
    \row
        \li The Qt xcb platform plugin
        \li {2, 1} \c platforms\libqxcb.so
    \row
        \li The Qt Core module
        \li {2, 1} \c libQt5Core.so.5
    \row
        \li The Qt GUI module
        \li {2, 1} \c libQt5Gui.so.5
    \row
        \li The Qt Widgets module
        \li {2, 1} \c libQt5Widgets.so.5
    \endtable

    On most systems, the extension for shared libraries is \c .so. A
    notable exception is HP-UX, which uses \c .sl.

    Remember that if your application depends on compiler specific
    libraries, these must still be redistributed along with your
    application. For more information, see the \l {Application
    Dependencies} section.

    To verify that the application now can be successfully deployed,
    you can extract this archive on a machine without Qt and without
    any compiler installed, and try to run it, i.e. run the \c
    plugandpaint.sh script.

    An alternative to putting the plugins in the \c plugins
    subdirectory is to add a custom search path when you start your
    application using QApplication::addLibraryPath() or
    QApplication::setLibraryPaths().

    \snippet snippets/code/doc_src_deployment.cpp 9

    \section1 Application Dependencies

    \section2 Additional Libraries

    To find out which libraries your application depends on, run the
    \c ldd tool (available on most Unices):

    \snippet snippets/code/doc_src_deployment.qdoc 10

    This will list all the shared library dependencies for your
    application. Depending on configuration, these libraries must be
    redistributed along with your application. In particular, the
    standard C++ library must be redistributed if you're compiling
    your application with a compiler that is binary incompatible with
    the system compiler. When possible, the safest solution is to link
    against these libraries statically.

    You will probably want to link dynamically with the regular X11
    libraries, since some implementations will try to open other
    shared libraries with \c dlopen(), and if this fails, the X11
    library might cause your application to crash.

    It's also worth mentioning that Qt will look for certain X11
    extensions, such as Xinerama and Xrandr, and possibly pull them
    in, including all the libraries that they link against. If you
    can't guarantee the presence of a certain extension, the safest
    approach is to disable it when configuring Qt (e.g. \c {./configure
    -no-xrandr}).

    FontConfig and FreeType are other examples of libraries that
    aren't always available or that aren't always binary
    compatible. As strange as it may sound, some software vendors have
    had success by compiling their software on very old machines and
    have been very careful not to upgrade any of the software running
    on them.

    When linking your application against the static Qt libraries, you
    must explicitly link with the dependent libraries mentioned
    above. Do this by adding them to the \c LIBS variable in your
    project file.

    \section2 Qt Plugins

    All Qt GUI applications require a plugin that implements the \l {Qt
    Platform Abstraction} (QPA) layer in Qt. For Linux/X11, the name of the
    platform plugin is \c {libqxcb.so}. This file must be located within a
    specific subdirectory (by default, \c platforms) under your distribution
    directory. Alternatively, it is possible to adjust the search path Qt
    uses to find its plugins, as described below.

    Your application may also depend on one or more Qt plugins, such
    as the JPEG image format plugin or a SQL driver plugin. Be sure
    to distribute any Qt plugins that you need with your application.
    Similar to the platform plugin, each type of plugin must be located
    within a specific subdirectory (such as \c imageformats or \c sqldrivers)
    within your distribution directory.

    The search path for Qt plugins (as well as a few other paths) is
    hard-coded into the QtCore library. By default, the first plugin
    search path will be hard-coded as \c /path/to/Qt/plugins. As
    mentioned above, using predetermined paths has certain
    disadvantages, so you need to examine various alternatives to make
    sure that the Qt plugins are found:

    \list

    \li \l{qt-conf.html}{Using \c qt.conf}. This is the recommended
    approach since it provides the most flexibility.

    \li Using QApplication::addLibraryPath() or
    QApplication::setLibraryPaths().

    \li Using a third party installation utility or the target system's
    package manager to change the hard-coded paths in the QtCore
    library.

    \endlist

    The \l{How to Create Qt Plugins} document outlines the issues you
    need to pay attention to when building and deploying plugins for
    Qt applications.
*/

/*!
    \page linux-issues.html
    \title Qt for Linux/X11 - Specific Issues
    \brief A description of issues with Qt that are specific to Linux/X11.

    This page contains information about the X11 platforms Qt is currently
    known to run on, with links to platform-specific notes.

    \section1 Linux

    There are no known problems with using Qt on Linux. For information
    about the specific compilers and distributions supported, visit the
    \l{Supported Platforms}{supported platforms} page.
*/
