Display Privileges

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We often have to generate an X-window display on one computer and display it on another one. The permissions and flags that have to be set for this to happen are different on the Vax and Unix systems.

Server Machine

The host which actually paints the screen (as opposed to the host which updates information in a window within the screen) is often referred to as the Display Server. It must be told to accept displays from the computer which is going to generate a window, referred to the Client. The default behaviour of the Display Server is to deny all requests for display. You can override it as follows. Note that the client machine must also be instructed to send its display to the right place.

If the Display Server is a Unix based, xhost + morgan01.slac.stanford.edu will let the computer morgan01.slac.stanford.edu to put up windows. Replace the "+" with a "-" to undo access. Changes are in effect for this one session only, i.e. you need to issue the command again the next time.

If the Display Server is Vax based, do the following. From the Session Manager, select Options -> Security.... Enter the node name, e.g. esaw01.slac.stanford.edu, whose displays you will accept. Set Username to *, and Transport to tcpip. See the example below.

Click Add, and Apply. Then click OK to get out. To make these changes your default for future sessions, select Options -> Save Session Manager.

Details, details...

You can omit the node name when issuing the xhost + command on a Unix Server. This will allow everyone to send displays to your window -- generally considered to be a bad idea.

If both the Client and the Server are Vax based, you could substitute decnet for tcpip. This is very unlikely to be the case for us.