Send a message to Linux desktop user from a console

The xmessage tool lets you display a popup window to users with a text message inside.

First install xmessage

# yum install xmessage

$ DISPLAY=:0 xmessage -nearmouse "Hello"

where options include:
    -file filename              file to read message from, "-" for stdin
    -buttons string             comma-separated list of label:exitcode
    -default button            button to activate if Return is pressed
    -print                         print the button label when selected
    -center                       pop up at center of screen
    -nearmouse                 pop up near the mouse cursor
    -timeout secs               exit with status 0 after "secs" seconds