X Window System
The X Window System (also called X Windows or X) is an open standard for windowing systems. The current version of X since 1994 is version 11 revision 6 (X11R6) but there are also many extensions.
X11R6 is standard on many Unix and Linux systems. By itself the X program (the "X server") supplies only mechanism which means that it requires programs running on top to provide a useful operating environment. The first such program is the Window Manager which handles window borders, stacking, workspaces and other functions. A window manager is sometimes part of a suite of programs called a Desktop Environment which provides even more functionality and a unified look and feel between programs.
Communication between X server and "client" programs is done over the "X protocol" which is able to run over TCP/IP sockets. Such sockets can in turn be forwarded over Secure Shell (SSH). This allows desktops and programs to be run remotely. There are X forwarding programs also for e.g. Microsoft Windows and MacOS.
Changing keyboard layout
xmodmap is a command-line utility that provides fine-grained control of the keymap. It does not have macro support.
GNOME 2, Mate
Keyboard layout and other settings can be selected in the program "gnome-keyboard-properties". It is available in the menu System→Preferences→Keyboard.
Criticism and deprecation
The X Window System specification itself has not been revised since the mid '90s, even though many various extensions have appeared. It has been criticised for its low performance and lack of modernity.
One replacement project stands out: "Wayland". Several Linux distributions as of 2018 run Wayland by default but allow X11 as an option and/or to run X11 applications on Wayland.
- x.org - The home for the X Consortium which manages the X protocol and reference implementation.
- Wikipedia - X Window System