1MESG(1P) POSIX Programmer's Manual MESG(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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12 mesg - permit or deny messages
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15 mesg [y|n]
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18 The mesg utility shall control whether other users are allowed to send
19 messages via write, talk, or other utilities to a terminal device. The
20 terminal device affected shall be determined by searching for the first
21 terminal in the sequence of devices associated with standard input,
22 standard output, and standard error, respectively. With no arguments,
23 mesg shall report the current state without changing it. Processes with
24 appropriate privileges may be able to send messages to the terminal
25 independent of the current state.
26
28 None.
29
31 The following operands shall be supported in the POSIX locale:
32 y Grant permission to other users to send messages to the terminal
34 device.
35 n Deny permission to other users to send messages to the terminal
37 device.
38
41 Not used.
42
44 None.
45
47 The following environment variables shall affect the execution of mesg:
48 LANG Provide a default value for the internationalization variables
50 that are unset or null. (See the Base Definitions volume of
51 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
52 ables for the precedence of internationalization variables used
53 to determine the values of locale categories.)
54 LC_ALL If set to a non-empty string value, override the values of all
56 the other internationalization variables.
57 LC_CTYPE
59 Determine the locale for the interpretation of sequences of
60 bytes of text data as characters (for example, single-byte as
61 opposed to multi-byte characters in arguments).
62 LC_MESSAGES
64 Determine the locale that should be used to affect the format
65 and contents of diagnostic messages written (by mesg) to stan‐
66 dard error.
67 NLSPATH
69 Determine the location of message catalogs for the processing of
70 LC_MESSAGES .
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74 Default.
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77 If no operand is specified, mesg shall display the current terminal
78 state in an unspecified format.
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81 The standard error shall be used only for diagnostic messages.
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84 None.
85
87 None.
88
90 The following exit values shall be returned:
91 0 Receiving messages is allowed.
93 1 Receiving messages is not allowed.
95 >1 An error occurred.
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100 Default.
101 The following sections are informative.
103
105 The mechanism by which the message status of the terminal is changed is
106 unspecified. Therefore, unspecified actions may cause the status of the
107 terminal to change after mesg has successfully completed. These actions
108 may include, but are not limited to: another invocation of the mesg
109 utility, login procedures; invocation of the stty utility, invocation
110 of the chmod utility or chmod() function, and so on.
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113 None.
114
116 The terminal changed by mesg is that associated with the standard
117 input, output, or error, rather than the controlling terminal for the
118 session. This is because users logged in more than once should be able
119 to change any of their login terminals without having to stop the job
120 running in those sessions. This is not a security problem involving the
121 terminals of other users because appropriate privileges would be
122 required to affect the terminal of another user.
123 The method of checking each of the first three file descriptors in
125 sequence until a terminal is found was adopted from System V.
126 The file /dev/tty is not specified for the terminal device because it
128 was thought to be too restrictive. Typical environment changes for the
129 n operand are that write permissions are removed for others and group
130 from the appropriate device. It was decided to leave the actual
131 description of what is done as unspecified because of potential differ‐
132 ences between implementations.
133 The format for standard output is unspecified because of differences
135 between historical implementations. This output is generally not useful
136 to shell scripts (they can use the exit status), so exact parsing of
137 the output is unnecessary.
138
140 None.
141
143 talk, write()
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146 Portions of this text are reprinted and reproduced in electronic form
147 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
148 -- Portable Operating System Interface (POSIX), The Open Group Base
149 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
150 Electrical and Electronics Engineers, Inc and The Open Group. In the
151 event of any discrepancy between this version and the original IEEE and
152 The Open Group Standard, the original IEEE and The Open Group Standard
153 is the referee document. The original Standard can be obtained online
154 at http://www.opengroup.org/unix/online.html .
155IEEE/The Open Group 2003 MESG(1P)