How can I specify a display?

Question

When I run some programs over SSH, such as firefox &, I get an error

Error: no display specified 

I would like to open ma

Answer 1

When you are connecting to another machine over SSH, you can enable X-Forwarding in SSH, so that X windows are forwarded encrypted through the SSH tunnel back to your machine. You can enable X forwarding by appending -X to the ssh command line or setting ForwardX11 yes in your SSH config file.

To check if the X-Forwarding was set up successfully (the server might not allow it), just try if echo $DISPLAY outputs something like localhost:10.0.