ssh and sudo but no $DISPLAY

Another solution is to merge the .Xauthority file of the current user with that of the root user.

1. ssh user@host
2. change the .Xauthority file permissions so that root also has access to it.
3. sudo su - root
4. xauth merge /home/users/user/.Xauthority

Test

gedit somefile.log

It should open a gedit window.

Solution found. An alternative method copied from this blog Using this script

userfirst=sshloginuser
usersecond=sudoorsuuser

$usersecond@host$

    su - $userfirst -c 'xauth list' |\
         grep `echo $DISPLAY |\
             cut -d ':' -f 2 |\
             cut -d '.' -f 1 |\
             sed -e s/^/:/`  |\
         xargs -n 3 xauth add

Or simply Logging as user1

xauth list

su or sudo su user2

xauth add OUTPUTOFXAUTHLIST

This might be an old post, but I solved this permanently linking (in server) my sudoer user .Xauthority file with the root one:

sudo ln -s /home/userWithPrivileges/.Xauthority /root/.Xauthority

This way I don't have to do anything else ever, I can now launch any GUI app with or without sudo.