PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

MESG(1P)                  POSIX Programmer's Manual                 MESG(1P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       mesg — permit or deny messages

SYNOPSIS         top

       mesg [y|n]

DESCRIPTION         top

       The mesg utility shall control whether other users are allowed to
       send messages via write, talk, or other utilities to a terminal
       device. The terminal device affected shall be determined by searching
       for the first terminal in the sequence of devices associated with
       standard input, standard output, and standard error, respectively.
       With no arguments, mesg shall report the current state without
       changing it. Processes with appropriate privileges may be able to
       send messages to the terminal independent of the current state.

OPTIONS         top

       None.

OPERANDS         top

       The following operands shall be supported in the POSIX locale:

       y         Grant permission to other users to send messages to the
                 terminal device.

       n         Deny permission to other users to send messages to the
                 terminal device.

STDIN         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       The following environment variables shall affect the execution of
       mesg:

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base Definitions
                 volume of POSIX.1‐2008, Section 8.2, Internationalization
                 Variables for the precedence of internationalization
                 variables used to determine the values of locale
                 categories.)

       LC_ALL    If set to a non-empty string value, override the values of
                 all the other internationalization variables.

       LC_CTYPE  Determine the locale for the interpretation of sequences of
                 bytes of text data as characters (for example, single-byte
                 as opposed to multi-byte characters in arguments).

       LC_MESSAGES
                 Determine the locale that should be used to affect the
                 format and contents of diagnostic messages written (by
                 mesg) to standard error.

       NLSPATH   Determine the location of message catalogs for the
                 processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS         top

       Default.

STDOUT         top

       If no operand is specified, mesg shall display the current terminal
       state in an unspecified format.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       The following exit values shall be returned:

        0    Receiving messages is allowed.

        1    Receiving messages is not allowed.

       >1    An error occurred.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       The mechanism by which the message status of the terminal is changed
       is unspecified. Therefore, unspecified actions may cause the status
       of the terminal to change after mesg has successfully completed.
       These actions may include, but are not limited to: another invocation
       of the mesg utility, login procedures; invocation of the stty
       utility, invocation of the chmod utility or chmod() function, and so
       on.

EXAMPLES         top

       None.

RATIONALE         top

       The terminal changed by mesg is that associated with the standard
       input, output, or error, rather than the controlling terminal for the
       session. This is because users logged in more than once should be
       able to change any of their login terminals without having to stop
       the job running in those sessions.  This is not a security problem
       involving the terminals of other users because appropriate privileges
       would be required to affect the terminal of another user.

       The method of checking each of the first three file descriptors in
       sequence until a terminal is found was adopted from System V.

       The file /dev/tty is not specified for the terminal device because it
       was thought to be too restrictive. Typical environment changes for
       the n operand are that write permissions are removed for others and
       group from the appropriate device. It was decided to leave the actual
       description of what is done as unspecified because of potential
       differences between implementations.

       The format for standard output is unspecified because of differences
       between historical implementations. This output is generally not
       useful to shell scripts (they can use the exit status), so exact
       parsing of the output is unnecessary.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       talk(1p), write(1p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
       Variables

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                            MESG(1P)

Pages that refer to this page: talk(1p)who(1p)write(1p)