9.4 X

The X Window System is provided by XFree86. There are two major versions of X server available on the Debian system: XFree86 Version 3.3 (XF3) and XFree86 Version 4.x series (XF4) both based on X11R6 specifications by X.Org.

For the basics of X, refer to X(7), the LDP XWindow-User-HOWTO, and the Remote X Apps mini-HOWTO. For a Debian-specific user guide, read /usr/share/doc/xfree86-common/FAQ.gz provided in the xfree86-common package. This contains an interesting and authoritative review of the key binding issues by Branden Robinson.

The X server, Section 9.4.3

a program on a local host that displays an X window and/or desktop on a user's monitor (CRT, LCD) and accepts keyboard and mouse input.

X clients, Section 9.4.4

a program on a (local or remote) host that runs X-compatible application software.

This reverses the ordinary use of "server" and "client" in other contexts.

There are several ways of getting the "X server" (display side) to accept remote connections from an "X client" (application side):

• xhost method

  • the host list mechanism (very insecure).

  • non-encrypted protocol (prone to eavesdropping attack).

  • Do not use this, if possible.

  • See Connecting to a remote X server – xhost, Section 9.4.7 and xhost(1x).

• xauth method

  • the MIT magic cookie mechanism (insecure but better than xhost).

  • non-encrypted protocol (prone to eavesdropping attack).

  • use this only for local connection since it is less CPU-intensive than ssh -X.

  • See Getting root in X, Section 9.4.12 and xauth(1x).

• xdm, wdm, gdm, kdm, ... methods

  • the MIT magic cookie mechanism (insecure as xauth).

  • See xdm(1x) and Xsecurity(7) for the basics of X display access control.

  • See wdm(1x), gdm(8), and kdm.options(5) for more information, if these are installed.

  • See Customizing runlevels, Section 2.4.3 for how to disable xdm to gain a Linux console upon boot without purging the xdm package.

• ssh -X method

  • port forwarding mechanism through secure shell (secure).

  • encrypted protocol (a waste of resources if used locally).

  • use this for remote connections.

  • See Connecting to a remote X server – ssh, Section 9.4.8.

All remote connection methods, except ssh, require TCP/IP connection enabled on the X server. See Using X over TCP/IP, Section 9.4.6.