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The environment variable DISPLAY tells all X clients, including Emacs, where to display their windows. Its value is set by default in ordinary circumstances, when you start an X server and run jobs locally. You can specify the display yourself; one reason to do this is if you want to log into another system and run Emacs there, and have the window displayed at your local terminal.
DISPLAY has the syntax ‘host:display.screen’, where host is the host name of the X Window System server machine, display is an arbitrarily-assigned number that distinguishes your server (X terminal) from other servers on the same machine, and screen is a field that allows an X server to control multiple terminal screens. The period and the screen field are optional. If included, screen is usually zero.
For example, if your host is named ‘glasperle’ and your server is the first (or perhaps the only) server listed in the configuration, your DISPLAY is ‘glasperle:0.0’.
You can specify the display name explicitly when you run Emacs, either by changing the DISPLAY variable, or with the option ‘-d display’ or ‘--display=display’. Here is an example:
emacs --display=glasperle:0 &
You can inhibit the use of the X window system with the ‘-nw’ option. Then Emacs uses its controlling text terminal for display. See Initial Options.
Sometimes, security arrangements prevent a program on a remote system from displaying on your local system. In this case, trying to run Emacs produces messages like this:
Xlib: connection to "glasperle:0.0" refused by server
You might be able to overcome this problem by using the xhost command on the local system to give permission for access from your remote machine.