tele

From User Cron

[cron time] [export DISPLAY=:0] ; [command or path to script]

Example:

* * * * * export DISPLAY=:0  ; xmessage -center -buttons Ok:0 "Hello world"

From Root Cron

[cron time] [export DISPLAY=:0] ; [sudo -u user_name or su user_name] [command or path to script]

Example:

* * * * * export DISPLAY=:0  ; sudo -u tele xmessage -center -buttons Ok:0 "Hello world"

Warning:

If you run script at computer startup, for example:

@reboot /your/script

And command or script does not show GUI, try add time, for example:

@reboot sleep 120 && /your/script