V7/usr/man/man1/mesg.1

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.TH MESG 1 
.SH NAME
mesg  \-  permit or deny messages
.SH SYNOPSIS
.B mesg
[
.B n
] [
.B y
]
.SH DESCRIPTION
.I Mesg
with argument
.B n
forbids messages via
.IR  write (1)
by revoking non-user
write permission on the user's terminal.
.I Mesg
with argument
.B y
reinstates permission.
All by itself,
.I mesg
reports the current state without changing it.
.SH FILES
/dev/tty*
.br
/dev
.SH "SEE ALSO"
write(1)
.SH DIAGNOSTICS
Exit status is 0 if messages are receivable,
1 if not, 2 on error.