Tip

docs.it4i/general/accessing-the-clusters/graphical-user-interface/x-window-system.md

@@ -28,10 +28,15 @@ Then log in as usual.
 In order to display graphical user interface GUI of various software tools, you need to enable the X display forwarding. Log in using the -X option in ssh client:
 
 ```console
- local $ export DISPLAY=localhost:0.0
  local $ ssh -X username@cluster-name.it4i.cz
 ```
 
+!!! tip
+    If unable to execute graphical sofware showing error message "cannot open display" then try export DISPLAY variable before log in using the -X option in ssh client:
+```console
+ local $ export DISPLAY=localhost:0.0
+```
+
 ## Verify the Forwarding
 
 To verify the forwarding, type