PWB1/usr/man/man8/wall.8

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.th WALL VIII 5/31/77
.sh NAME
wall  \*-  write to all users
.sh SYNOPSIS
.bd /etc/wall
.sh DESCRIPTION
.it Wall
reads its standard input until an end-of-file.
It then sends this message to all currently
logged in users preceded by
``Broadcast Message ...''.
It is used to warn all users,
typically prior to shutting down the system.
.s3
The super-user can send to all people logged in,
regardless of protections;
if used immoderately,
this is a quick way to become unpopular.
.sh FILES
/dev/tty?
.sh "SEE ALSO"
mesg(I), write(I)
.sh DIAGNOSTICS
``Cannot send to ...'' when the open on
a user's tty file fails.