WALL(1)
NAME
wall − write to all users on a node
USAGE
wall
DESCRIPTION
The wall command reads its standard input until an end-of-file. It then sends the specified message, preceded by “Broadcast Message ...”, to users logged-in on the node from which you are writing. This means that the message will appear in a pad on the transmitting node, as well as on the screen or output device of anyone logged onto the node via SIO lines or ttys.
The sender should be super-user to override any protections that the users may have invoked.
FILES
/dev/pty? device filenames
/dev/sio? device filenames
/etc/utmp to find user
DIAGNOSTICS
“Cannot send to ...” when the open on a user’s tty or sio file fails.