WALL(1) BSD General Commands Manual WALL(1)
wall - write a message to users
Wall displays the contents of file or, by default, its standard input, on
the terminals of all currently logged in users.
Only the super-user can write on the terminals of users who have chosen
to deny messages or are using a program which automatically denies mes
Reading from a file is refused when the invoker is not superuser and the
program is suid or sgid.
mesg(1), talk(1), write(1), shutdown(8)
A wall command appeared in Version 7 AT&T UNIX.
Linux 0.99 March 8, 1993 Linux 0.99