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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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MSGCTL(3P) POSIX Programmer's Manual MSGCTL(3P)
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.
msgctl — XSI message control operations
#include <sys/msg.h>
int msgctl(int msqid, int cmd, struct msqid_ds *buf);
The msgctl() function operates on XSI message queues (see the Base
Definitions volume of POSIX.1‐2017, Section 3.226, Message Queue).
It is unspecified whether this function interoperates with the
realtime interprocess communication facilities defined in Section
2.8, Realtime.
The msgctl() function shall provide message control operations as
specified by cmd. The following values for cmd, and the message
control operations they specify, are:
IPC_STAT Place the current value of each member of the msqid_ds
data structure associated with msqid into the
structure pointed to by buf. The contents of this
structure are defined in <sys/msg.h>.
IPC_SET Set the value of the following members of the msqid_ds
data structure associated with msqid to the
corresponding value found in the structure pointed to
by buf:
msg_perm.uid
msg_perm.gid
msg_perm.mode
msg_qbytes
Also, the msg_ctime timestamp shall be set to the
current time, as described in Section 2.7.1, IPC
General Description.
IPC_SET can only be executed by a process with
appropriate privileges or that has an effective user
ID equal to the value of msg_perm.cuid or msg_perm.uid
in the msqid_ds data structure associated with msqid.
Only a process with appropriate privileges can raise
the value of msg_qbytes.
IPC_RMID Remove the message queue identifier specified by msqid
from the system and destroy the message queue and
msqid_ds data structure associated with it. IPC_RMD
can only be executed by a process with appropriate
privileges or one that has an effective user ID equal
to the value of msg_perm.cuid or msg_perm.uid in the
msqid_ds data structure associated with msqid.
Upon successful completion, msgctl() shall return 0; otherwise, it
shall return -1 and set errno to indicate the error.
The msgctl() function shall fail if:
EACCES The argument cmd is IPC_STAT and the calling process does
not have read permission; see Section 2.7, XSI Interprocess
Communication.
EINVAL The value of msqid is not a valid message queue identifier;
or the value of cmd is not a valid command.
EPERM The argument cmd is IPC_RMID or IPC_SET and the effective
user ID of the calling process is not equal to that of a
process with appropriate privileges and it is not equal to
the value of msg_perm.cuid or msg_perm.uid in the data
structure associated with msqid.
EPERM The argument cmd is IPC_SET, an attempt is being made to
increase to the value of msg_qbytes, and the effective user
ID of the calling process does not have appropriate
privileges.
The following sections are informative.
None.
The POSIX Realtime Extension defines alternative interfaces for
interprocess communication (IPC). Application developers who need
to use IPC should design their applications so that modules using
the IPC routines described in Section 2.7, XSI Interprocess
Communication can be easily modified to use the alternative
interfaces.
None.
None.
Section 2.7, XSI Interprocess Communication, Section 2.8,
Realtime, mq_close(3p), mq_getattr(3p), mq_notify(3p),
mq_open(3p), mq_receive(3p), mq_send(3p), mq_setattr(3p),
mq_unlink(3p), msgget(3p), msgrcv(3p), msgsnd(3p)
The Base Definitions volume of POSIX.1‐2017, Section 3.226,
Message Queue, sys_msg.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 MSGCTL(3P)
Pages that refer to this page: sys_msg.h(0p), ipcrm(1p), mq_close(3p), mq_getattr(3p), mq_notify(3p), mq_open(3p), mq_receive(3p), mq_setattr(3p), mq_unlink(3p), msgget(3p), msgrcv(3p), msgsnd(3p)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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