wall - Sends a message to all users
The wall command reads from standard input until you press the End-of-File key sequence, or takes its input from the contents of file if you specify it, and sends the input as a message to all users who are logged in. The message is preceded by the heading:
Broadcast Message from user@node (tty) at hh:mm
where user is the user invoking wall, node and tty are the node and terminal of that user, and hh:mm is the time of the message.
To override any protections other users have set up, you must be operating with superuser authority. Typically, the root user uses wall to warn all users of an impending system shutdown.
command sends messages to the local node
To suspend error messages.
Commands: mesg(1), su(1), talk(1), write(1)