V4/man/man1/mesg.1

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.th MESG I 3/15/72
.sh NAME
mesg  \*-  permit or deny messages
.sh SYNOPSIS
.bd mesg
[
.bd n
] [
.bd y
]
.sh DESCRIPTION
.it Mesg
with argument
.bd n
forbids messages via
.it write
by revoking non-user
write permission on the user's typewriter.
.it Mesg
with argument
.bd y
reinstates permission.
All by itself,
.it mesg
reverses the current permission.
In all cases the previous state is reported.
.sh FILES
/dev/tty?
.sh "SEE ALSO"
write(I)
.sh DIAGNOSTICS
`?' if the standard input file is not a typewriter
.sh BUGS