/etc/X11 : Configuration for the X Window System (optional)

/etc/X11 is the location for all X11 host-specific configuration. This directory is necessary to allow local control if /usr is mounted read only.

The following files, or symbolic links to files, must be in /etc/X11 if the corresponding subsystem is installed:

File Description
Xconfig The configuration file for early versions of XFree86 (optional)
XF86Config The configuration file for XFree86 versions 3 and 4 (optional)
Xmodmap Global X11 keyboard modification file (optional)

Subdirectories of /etc/X11 may include those for xdm and for any other programs (some window managers, for example) that need them. We recommend that window managers with only one configuration file which is a default .*wmrc file must name it system.*wmrc (unless there is a widely-accepted alternative name) and not use a subdirectory. Any window manager subdirectories must be identically named to the actual window manager binary.