The Xorg server relies on the operating system's native module loader support for handling program modules. The X server makes use of modules for video drivers, X server extensions, input device drivers, framebuffer layers, and internal components used by some drivers (like XAA & EXA).

The module interfaces (both API and ABI) used in this release are subject to change without notice. While we will attempt to provide backward compatibility for the module interfaces in stable releases, we cannot guarantee this. Compatibility in the other direction is explicitly not guaranteed because new modules may rely on interfaces added in new releases, nor is compatibility across stable release branches (such as between Xorg 1.11 and 1.12).

The Xorg server uses a configuration file as the primary mechanism for providing configuration and run-time parameters. The configuration file format is described in detail in the xorg.conf(5) manual page.

Note that this release features significant improvements for running the server without a configuration file, so many users may find that that they don't need a configuration file, or may rely on just snippets of configuration placed in the xorg.conf.d directory.

If you do need to customize the configuration file, see the xorg.conf manual page . You can also check the driver-specific manual pages and the related documentation (found at driver tables) also.

The recommended method for generating a configuration file is to use the Xorg server itself. Run as root:

        Xorg -configure
        

and follow the instructions.

Command line options can be used to override some default parameters and parameters provided in the configuration file. Command line options available for use with all X servers in this release are described in the Xserver(1) manual page. Command line options specific to the Xorg server are described in the Xorg(1) manual page.

Some multi-head configurations are supported in X11R7.7. Support for multiple PCI/AGP cards may require a kernel with changes to support VGA arbitration.

One of the main problems is with drivers not sufficiently initializing cards that were not initialized at boot time. This has been improved somewhat with the INT10 support that is used by most drivers (which allows secondary card to be "soft-booted", but in some cases there are other issues that still need to be resolved. Some combinations can be made to work better by changing which card is the primary card (either by using a different PCI slot, or by changing the system BIOS's preference for the primary card).

Xinerama is an X server extension that allows multiple physical screens connected to multiple video devices to behave as a single screen. With traditional multi-head in X11, windows cannot span or cross physical screens. Xinerama removes this limitation. Xinerama does, however, require that the physical screens all have the same root depth, so it isn't possible, for example, to use an 8-bit screen together with a 16-bit screen in Xinerama mode.

Xinerama is not enabled by default, and can be enabled with the +xinerama command line option for the X server. Note that enabling Xinerama may disable certain other extensions which are not compatible with Xinerama.

The VESA® Display Data Channel (DDC™) standard allows the monitor to tell the video card (or in some cases the computer directly) about itself; particularly the supported screen resolutions and refresh rates.

Partial or complete DDC support is available in most of the video drivers. DDC is enabled by default, but can be disabled with a "Device" section entry: Option "NoDDC". We have support for DDC versions 1 and 2; these can be disabled independently with Option "NoDDC1" and Option "NoDDC2".

At startup the server prints out DDC information from the display, and can use this information to set the default monitor parameters, or to warn about monitor sync limits if those provided in the configuration file don't match those that are detected.

Direct rendered OpenGL® support is provided for several hardware platforms by the Direct Rendering Infrastructure (DRI). Further information about DRI can be found at the DRI Project's web site. The 3D core rendering component is provided by Mesa.

Of note is that this release supports building the X server using the system-wide libdrm. Previously, drm was kept in the server's tree and loaded as a module, rather than using the standard OS mechanisms for managing shared libraries of code. This requires that the server be built using a version of libdrm of 2.3.0 or newer if it is to use DRM.

The Xorg server has previously allowed users to exit the server by pressing the keys Control + Alt + Backspace. While this function is still enabled by default in this release, the keymap data usually used with Xorg, from the xkeyboard-config project, has been modified to not map that sequence by default, in order to reduce the chance that inexperienced users will accidentally destroy their work.

Users who wish to have this functionality available by default may enable it via the XKB configuration option “terminate:ctrl_alt_bksp”. For instance, the setxkbmap command can be used to enable this by running:

	setxkbmap -option "terminate:ctrl_alt_bksp"
	  

The XKB Configuration Guide also includes an example xorg.conf.d file that sets the “terminate:ctrl_alt_bksp” option by default on all keyboards. Many desktop environments include XKB configuration options in their preferences to enable this as well.

The Xorg server in this release provides various functions that can be mapped to keystrokes to aid in the debugging of programs with errant input grabs.

The keysyms XF86LogGrabInfo and XF86LogWindowTree are defined to print information to the Xorg log file on the current set of input grabs, and the window tree of the current display. By default, these are available for use, but not mapped to any key.

The keysym XF86Ungrab forces the X server to release all active grabs, which may leave the clients holding them in an inconsistent state. XF86ClearGrab goes further, killing the client connection of any client holding an active grab when it is pressed. These keystrokes are intended to allow developers to debug clients which are not properly releasing grabs or have problems occur while input is grabbed. Since grabs are a fundamental part of the X client security model, these keystrokes come with risks, such as the ability to bypass or kill screen locks without knowing the password, and thus are not available by default.

Users who are willing to accept the security risk and wish to enable this functionality may do so via the XKB configuration option “grab:break_actions”.

The X servers in the X11R7.7 release now start by default with an empty black screen and do not draw the mouse cursor until a client sets the cursor image. To restore the classic behavior of starting with the grey weave pattern and × cursor, start the X server with the -retro option.

Previous versions of X installed font files under the lib/X11/fonts subdirectory of the X installation directory (for instance, in X11R6 releases, /usr/X11R6/lib/X11/fonts was commonly used). This release uses the default installation path of the fonts subdirectory of the datadir setting from the GNU autoconf configuration. For instance, if the fonts are configured with ./configure --prefix=/usr, they will be installed under subdirectories of /usr/share/fonts/X11. The font module configure scripts all take an option of --with-fontrootdir=PATH to override the default. If --with-fontrootdir is not specified, the fontutil pkg-config file will be consulted to find the fontrootdir specified when the fontutil module was installed.

The X11R7.7 release supports PCF format bitmap fonts stored uncompressed or compressed via the compress, gzip, or bzip2 programs. To utilize bzip2 compression, the libXfont and mkfontscale modules must be built with the --with-bzip2 — all other methods are enabled by default.

To specify which compression method to use when installing a font module from X11R7.7 the configure scripts accept an option of --with-compression=TYPE, where TYPE may be none, compress, gzip, or bzip2.

Previous versions of X came with two Postscript Type1 font backends. The functionality from the “Type1” backend has been replaced by the Type1 support in the “FreeType” backend.

The CID-keyed font format was designed by Adobe Systems for fonts with large character sets. The CID-keyed format is obsolete, as it has been superseded by other formats such as OpenType/CFF and support for CID-keyed fonts has been removed from X11.