wall(1)
Name
wall − write to all users
Syntax
wall
Description
The wall command reads its standard input until an EOF. It then sends this message, preceded by ‘Broadcast Message ...’, to all logged in users.
The sender should be super-user to override any protections the users may have invoked.
Diagnostics
‘Cannot send to ...’ when the open on a user’s tty file fails.
Files
/dev/tty?
/etc/utmp