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

Please do NOT try to set $DISPLAY manually when connecting over SSH.
If you connect via SSH -X and $DISPLAY stays empty, this usually means that no encrypted channel could be established.

Most likely you are missing the package xauth or xorg-x11-xauth. Try to install it on the remote machine using:

sudo apt-get install xauth

or

sudo apt-get install xorg-x11-xauth

After that end and restart your SSH connection. Don't forget to use SSH -X so that X Window output is forwarded to your local machine.

Now try echo $DISPLAYagain to see if $DISPLAY has been set automatically by the SSH demon. It should show you a line with an IP address and a port.