gdm-signal -V (return code: 1)
gdm-signal: Cannot open display:
gdm-signal --help (return code: 0)
Usage:
gdm-signal [OPTION...] - make the machine sleep in some way
Help Options:
-?, --help Show help options
--help-all Show all help options
--help-gtk Show GTK+ Options
Application Options:
-z, --hibernate Hibernate the machine
-h, --halt Halt the machine
-s, --suspend Suspend the machine
-r, --reboot Reboot the machine
--display=DISPLAY X display to use