Manual Page - mesg(1p)
Manual Reference Pages - MESG (P)
NAME
mesg - permit or deny messages
CONTENTS
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
SYNOPSIS
mesg [y|n]
DESCRIPTION
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
None.
OPERANDS
The following operands shall be supported in the POSIX locale:
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y
|
Grant permission to other users to send messages to the terminal device.
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n
|
Deny permission to other users to send messages to the terminal device.
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STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of
mesg:
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|
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LANG
|
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
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LC_ALL
|
If set to a non-empty string value, override the values of all the
other internationalization variables.
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LC_CTYPE
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| |
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).
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LC_MESSAGES
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Determine the locale that should be used to affect the format and
contents of diagnostic messages written (by mesg) to
standard error.
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NLSPATH
|
Determine the location of message catalogs for the processing of LC_MESSAGES
.
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ASYNCHRONOUS EVENTS
Default.
STDOUT
If no operand is specified, mesg shall display the current terminal
state in an unspecified format.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
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0
|
Receiving messages is allowed.
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1
|
Receiving messages is not allowed.
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>1
|
An error occurred.
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CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
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
None.
RATIONALE
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
None.
SEE ALSO
talk , write()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
| IEEE/The Open Group | MESG (P) | 2003 |
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