wall (Unix)

wall (an abbreviation of write to all) is a Unix command-line utility that displays the contents of a file or standard input to all logged-in users. It is typically used by root to send out shutting down message to all users just before poweroff.

Invocation

wall reads the message from standard input by default when the filename is omitted, that can be done by piping it with the echo command:

alice@sleipnir:~$ # `tty` to show the current terminal name
alice@sleipnir:~$ tty
/dev/pts/7
alice@sleipnir:~$ echo Remember to brush your teeth! | wall

The message may also be typed in much the same way cat is used; invoke wall by typing wall and press ↵ Enter followed by your message, press ↵ Enter and Ctrl+D:

alice@sleipnir:~$ wall
Remember to brush your teeth!
^D

And using a here-string:

alice@sleipnir:~$ wall <<<'Remember to brush your teeth!'

Reading from a file is also supported:

alice@sleipnir:~$ cat .important_announcement
Remember to brush your teeth!
alice@sleipnir:~$ wall .important_announcement # same as `wall !$`

All the commands above should display the following output on terminals that users allow write access to (see mesg(1)):

Broadcast Message from alice@sleipnir
  (/dev/pts/7) at 16:15 ...
 
Remember to brush your teeth!

References

• wall(1): send message to everybody's terminal – Linux User Commands Manual