mirror of https://github.com/mkerrisk/man-pages
161 lines
5.1 KiB
Groff
161 lines
5.1 KiB
Groff
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "MESG" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" mesg
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.SH NAME
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mesg \- permit or deny messages
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.SH SYNOPSIS
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.LP
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\fBmesg\fP \fB[\fP\fBy|n\fP\fB]\fP\fB\fP
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.SH DESCRIPTION
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.LP
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The \fImesg\fP utility shall control whether other users are allowed
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to send messages via \fIwrite\fP, \fItalk\fP, or other utilities to
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a terminal
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device. The terminal device affected shall be determined by searching
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for the first terminal in the sequence of devices associated
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with standard input, standard output, and standard error, respectively.
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With no arguments, \fImesg\fP shall report the current
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state without changing it. Processes with appropriate privileges may
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be able to send messages to the terminal independent of the
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current state.
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.SH OPTIONS
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.LP
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None.
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.SH OPERANDS
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.LP
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The following operands shall be supported in the POSIX locale:
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.TP 7
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\fIy\fP
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Grant permission to other users to send messages to the terminal device.
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.TP 7
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\fIn\fP
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Deny permission to other users to send messages to the terminal device.
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.sp
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.SH STDIN
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.LP
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Not used.
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.SH INPUT FILES
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.LP
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None.
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.SH ENVIRONMENT VARIABLES
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.LP
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The following environment variables shall affect the execution of
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\fImesg\fP:
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.TP 7
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\fILANG\fP
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Provide a default value for the internationalization variables that
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are unset or null. (See the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
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for
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the precedence of internationalization variables used to determine
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the values of locale categories.)
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.TP 7
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\fILC_ALL\fP
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If set to a non-empty string value, override the values of all the
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other internationalization variables.
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.TP 7
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\fILC_CTYPE\fP
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Determine the locale for the interpretation of sequences of bytes
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of text data as characters (for example, single-byte as
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opposed to multi-byte characters in arguments).
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.TP 7
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\fILC_MESSAGES\fP
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Determine the locale that should be used to affect the format and
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contents of diagnostic messages written (by \fImesg\fP) to
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standard error.
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.TP 7
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\fINLSPATH\fP
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Determine the location of message catalogs for the processing of \fILC_MESSAGES
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\&.\fP
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.sp
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.SH ASYNCHRONOUS EVENTS
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.LP
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Default.
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.SH STDOUT
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.LP
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If no operand is specified, \fImesg\fP shall display the current terminal
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state in an unspecified format.
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.SH STDERR
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.LP
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The standard error shall be used only for diagnostic messages.
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.SH OUTPUT FILES
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.LP
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None.
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.SH EXTENDED DESCRIPTION
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.LP
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None.
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.SH EXIT STATUS
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.LP
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The following exit values shall be returned:
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.TP 7
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\ 0
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Receiving messages is allowed.
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.TP 7
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\ 1
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Receiving messages is not allowed.
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.TP 7
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>1
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An error occurred.
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.sp
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.SH CONSEQUENCES OF ERRORS
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.LP
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Default.
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.LP
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\fIThe following sections are informative.\fP
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.SH APPLICATION USAGE
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.LP
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The mechanism by which the message status of the terminal is changed
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is unspecified. Therefore, unspecified actions may cause
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the status of the terminal to change after \fImesg\fP has successfully
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completed. These actions may include, but are not limited
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to: another invocation of the \fImesg\fP utility, login procedures;
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invocation of the \fIstty\fP utility, invocation of the \fIchmod\fP
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utility or
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\fIchmod\fP() function, and so on.
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.SH EXAMPLES
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.LP
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None.
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.SH RATIONALE
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.LP
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The terminal changed by \fImesg\fP is that associated with the standard
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input, output, or error, rather than the controlling
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terminal for the session. This is because users logged in more than
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once should be able to change any of their login terminals
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without having to stop the job running in those sessions. This is
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not a security problem involving the terminals of other users
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because appropriate privileges would be required to affect the terminal
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of another user.
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.LP
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The method of checking each of the first three file descriptors in
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sequence until a terminal is found was adopted from System
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V.
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.LP
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The file \fB/dev/tty\fP is not specified for the terminal device because
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it was thought to be too restrictive. Typical
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environment changes for the \fIn\fP operand are that write permissions
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are removed for \fIothers\fP and \fIgroup\fP from the
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appropriate device. It was decided to leave the actual description
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of what is done as unspecified because of potential differences
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between implementations.
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.LP
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The format for standard output is unspecified because of differences
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between historical implementations. This output is
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generally not useful to shell scripts (they can use the exit status),
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so exact parsing of the output is unnecessary.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fItalk\fP , \fIwrite\fP()
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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