Linux - DISPLAY (environment variable)

The magic word in the X window system is DISPLAY. A display consists (simplified) of:

• a keyboard,
• a mouse
• and a screen.

A display is managed by a server program, known as an X server. The server serves displaying capabilities to other programs that connect to it.

The remote server knows where it have to redirect the X network traffic via the definition of the DISPLAY environment variable which generally points to an X Display server located on your local computer.

The value of the display environment variable is:

hostname:D.S

where:

• hostname is the name of the computer where the X server runs. An omitted hostname means the localhost.
• D is a sequence number (usually 0). It can be varied if there are multiple displays connected to one computer.
• S is the screen number. A display can actually have multiple screens. Usually there's only one screen though where 0 is the default.

localhost:4
gerardnico.com:0
:0.0

• hostname:D.S means screen S on display D of host hostname; the X server for this display is listening at TCP port 6000+D.
• host/unix:D.S means screen S on display D of host host; the X server for this display is listening at UNIX domain socket /tmp/.X11-unix/XD (so it's only reachable from host).
• :D.S is equivalent to host/unix:D.S, where host is the local hostname.

Setting the DISPLAY variable, depend of your shell

• Bourne, Bash or Korn shell:

$ export DISPLAY=local_host:0.0      

• C shell

% setenv DISPLAY local_host:0.0

In this example, local_host is the host name or IP address of the local computer that you want to use to display for instance an installation screen such as Oracle Universal Installer.