Sometimes you find yourself having to redirect the X display to a different host but "ssh -X hostname" will not work since you had to switch users. For instance you logged to a host as root and afterwards "su - oracle".
$ ssh firstname.lastname@example.org -X # echo $DISPLAY localhost:10.0 # xauth list host1.domain.com/unix:11 MIT-MAGIC-COOKIE-1 95e4b887f2f6d132897aedbbbe297309 host1.domainom/unix:10 MIT-MAGIC-COOKIE-1 961e9e854127e3c70ff8804a5eb57f7e # su - oracle $ xauth add host1.domain.com/unix:10 MIT-MAGIC-COOKIE-1 961e9e854127e3c70ff8804a5eb57f7e xauth: creating new authority file /home/oracle/.Xauthority
Then trying xclock or xterm worked for me. If you still have a problem also try:
$ export DISPLAY=localhost:10.0