X11 forwarding for sudo users

Can’t
start X11 applications after “su” or “su -” to another user 
 To get access to the X client applications such as
system-config-date, xclock, vncviewer we need to export the DISPLAY
settings of a remote host to the local server. This is commonly done
using below commands. 
 # ssh root@remotehost  
 remotehost# export DISPLAY=x.x.x.x:y.y 
 Where x.x.x.x:y.y – is the display settings of the system from which
you connected to the remote host. 
 You can also use the -X option with ssh to directly export the
DISPLAY on the remote host. 
 # ssh -X root@remotehost 
 But now if you try to switch to another user on the remote system and
export the display again, you would get and error – “Error: Can’t open
display:”. 
 # ssh -X root@remotehost  
 # su - [username] 
 # export DISPLAY=x.x.x.x:y.y  
 # xclock 
 Error: Can't open display: x.x.x.x:y.y 
 X11 forwarding for sudo
users 
 Just setting the DISPLAY is not enough. X authentication is based on
cookies, so it’s necessary to set the cookie used by the user that
initiated the connection. The following procedure allows a sudo user to
use the ssh based X11 tunnel: 
 1. Connect the remote host using the -X option with ssh. 
 # ssh -X root@remote-host 
 2. Now list the coockie set for the current user. 
 # xauth list $DISPLAY 
 node01.thegeekdiary.com/unix:10

MIT-MAGIC-COOKIE-1

dacbc5765ec54a1d7115a172147866aa 
 # echo $DSIPLAY 
 localhost:10.0 
 3. Switch to another user account using sudo. Add the cookie from the
command output above to the sudo user. 
 # sudo su - [user]  
 # xauth add node01.thegeekdiary.com/unix:10

MIT-MAGIC-COOKIE-1

dacbc5765ec54a1d7115a172147866aa 
 4. Export the display from step 2 again for the sudo user. Try the
command xclock to verify if the x client applications are working as
expected. 
 # export DISPLAY=localhost:10.0 
 # xclock