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Church Of The
Swimming Elephant

Index | Description | Starting Up | Displays | Access Control | Geometry Specification
Window Managers | Fonts | Colors | Keyboards | Options | Resources | Examples | Diagnostics



From the user's prospective, every X server has a displayname of the form:
This information is used by the application to determine how it should connect to the server and which screen it should use by default (on displays with multiple monitors): hostname The hostname specifies the name of the machine to which the display is physically connected. If the hostname is not given, the most efficient way of communicating to a server on the same machine will be used. displaynumber

The phrase "display" is usually used to refer to collection of monitors that share a common keyboard and pointer (mouse, tablet, etc.). Most workstations tend to only have one keyboard, and therefore, only one display. Larger, multi-user systems, however, will frequently have several displays so that more than one person can be doing graphics work at once.

To avoid confusion, each display on a machine is assigned a displaynumber (beginning at 0) when the X server for that display is started. The display number must always be given in a display name.

Some displays share a single keyboard and pointer among two or more monitors. Since each monitor has its own set of windows, each screen is assigned a screen number (beginning at 0) when the X server for that display is started. If the screen number is not given, then screen 0 will be used.

On POSIX systems, the default display name is stored in your DISPLAY environment variable. This variable is set automatically by the xterm terminal emulator. However, when you log into another machine on a network, you'll need to set DISPLAY by hand to point to your display. For example,

% setenv DISPLAY myws:0 $ DISPLAY=myws:0; export DISPLAY
The xon script can be used to start an X program on a remote machine; it automatically sets the DISPLAY variable correctly. Finally, most X programs accept a command line option of -display displayname to temporarily override the contents of DISPLAY. This is most commonly used to pop windows on another person's screen or as part of a "remote shell" command to start an xterm pointing back to your display.

For example,

% xeyes -display joesws:0 -geometry 1000x1000+0+0 % rsh big xterm -display myws:0 -ls </dev/null &
X servers listen for connections on a variety of different communications channels (network byte streams, shared memory, etc.). Since there can be more than one way of contacting a given server, The hostname part of the display name is used to determine the type of channel (also called a transport layer) to be used. X servers generally support the following types of connections:

The hostname part of the display name should be the empty string.

For example:

:0, :1, and :0.1.
The most efficient local transport will be chosen.

The hostname part of the display name should be the server machine's IP address name. Full Internet names, abbreviated names, and IP addresses are all allowed. For example:, expo:0,, bigmachine:1, and hydra:0.1. DECnet The hostname part of the display name should be the server machine's nodename followed by two colons instead of one.

For example:

myws::0, big::1, and hydra::0.1.


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