mirror of https://github.com/mkerrisk/man-pages
225 lines
6.0 KiB
Groff
225 lines
6.0 KiB
Groff
.\" Copyright 1993 Giorgio Ciucci (giorgio@crcc.it)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified Sun Feb 18 01:59:29 2001 by Andries E. Brouwer <aeb@cwi.nl>
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.\" Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Added notes on CAP_IPC_OWNER requirement
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.\" Modified, 17 Jun 2004, Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Added notes on CAP_SYS_ADMIN requirement for IPC_SET and IPC_RMID
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.\" Modified, 11 Nov 2004, Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Language and formatting clean-ups
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.\" Added msqid_ds and ipc_perm structure definitions
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.\"
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.TH MSGCTL 2 2004-11-10 "Linux 2.6.9" "Linux Programmer's Manual"
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.SH NAME
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msgctl \- message control operations
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.SH SYNOPSIS
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.nf
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.B
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#include <sys/types.h>
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.B
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#include <sys/ipc.h>
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.B
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#include <sys/msg.h>
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.fi
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.sp
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.BI "int msgctl(int " msqid ,
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.BI "int " cmd ,
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.BI "struct msqid_ds *" buf );
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.SH DESCRIPTION
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.BR msgctl ()
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performs the control operation specified by
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.I cmd
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on the message queue with identifier
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.IR msqid .
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.PP
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The
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.I msqid_ds
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data structure is defined in <sys/msg.h> as follows:
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.nf
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.in +4n
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struct msqid_ds {
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struct ipc_perm msg_perm; /* Ownership and permissions
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time_t msg_stime; /* Time of last msgsnd() */
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time_t msg_rtime; /* Time of last msgrcv() */
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time_t msg_ctime; /* Time of last change */
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unsigned long __msg_cbytes; /* Current number of bytes in
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queue (non-standard) */
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msgqnum_t msg_qnum; /* Current number of messages
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in queue */
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msglen_t msg_qbytes; /* Maximum number of bytes
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allowed in queue */
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pid_t msg_lspid; /* PID of last msgsnd() */
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pid_t msg_lrpid; /* PID of last msgrcv() */
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};
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.in -4n
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.fi
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.PP
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The
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.I ipc_perm
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structure is defined in <sys/ipc.h> as follows
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(the highlighted fields are settable using
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.BR IPC_SET ):
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.PP
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.nf
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.in +4n
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struct ipc_perm {
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key_t key; /* Key supplied to msgget() */
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uid_t \fBuid\fP; /* Effective UID of owner */
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gid_t \fBgid\fP; /* Effective GID of owner */
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uid_t cuid; /* Effective UID of creator */
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gid_t cgid; /* Effective GID of creator */
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unsigned short \fBmode\fP; /* Permissions */
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unsigned short seq; /* Sequence number */
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};
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.in -4n
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.fi
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.PP
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Valid values for
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.I cmd
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are:
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.TP
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.B IPC_STAT
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Copy information from the kernel data structure associated with
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.I msqid
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into the
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.I msqid_ds
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structure pointed to by
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.IR buf .
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The caller must have read permission on the message queue.
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.TP
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.B IPC_SET
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Write the values of some members of the
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.I msqid_ds
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structure pointed to by
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.I buf
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to the kernel data structure associated with this message queue,
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updating also its
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.I msg_ctime
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member.
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The following members of the structure are updated:
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.IR msg_qbytes ,
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.IR msg_perm.uid ,
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.IR msg_perm.gid ,
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and (the least significant 9 bits of)
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.IR msg_perm.mode .
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The effective UID of the calling process must match the owner
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.RI ( msg_perm.uid )
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or creator
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.RI ( msg_perm.cuid )
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of the message queue, or the caller must be privileged.
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Appropriate privilege (Linux: the
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.B CAP_IPC_RESOURCE
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capability) is required to raise the
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.I msg_qbytes
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value beyond the system parameter
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.BR MSGMNB .
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.TP
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.B IPC_RMID
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Immediately remove the message queue,
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awakening all waiting reader and writer processes (with an error
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return and
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.I errno
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set to
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.BR EIDRM ).
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The calling process must have appropriate privileges
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or its effective user ID must be either that of the creator or owner
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of the message queue.
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.SH "RETURN VALUE"
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On success, the return value will be 0
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otherwise \-1
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with
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.I errno
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indicating the error.
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.SH ERRORS
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On failure,
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.I errno
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is set to one of the following:
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.TP 11
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.B EACCES
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The argument
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.I cmd
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is equal to
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.B IPC_STAT
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or
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.BR MSG_STAT ,
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but the calling process does not have read permission on the message queue
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.IR msqid ,
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and does not have the
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.B CAP_IPC_OWNER
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capability.
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.TP
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.B EFAULT
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The argument
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.I cmd
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has the value
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.B IPC_SET
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or
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.BR IPC_STAT ,
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but the address pointed to by
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.I buf
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isn't accessible.
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.TP
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.B EIDRM
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The message queue was removed.
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.TP
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.B EINVAL
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Invalid value for
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.I cmd
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or
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.IR msqid .
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.TP
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.B EPERM
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The argument
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.I cmd
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has the value
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.B IPC_SET
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or
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.BR IPC_RMID ,
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but the effective user ID of the calling process is not the creator
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(as found in
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.IR msg_perm.cuid )
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or the owner
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(as found in
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.IR msg_perm.uid )
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of the message queue,
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and the process is not privileged (Linux: it does not have the
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.B CAP_SYS_ADMIN
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capability).
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.SH NOTES
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Various fields in the \fIstruct msqid_ds\fP were shorts under Linux 2.2
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and have become longs under Linux 2.4. To take advantage of this,
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a recompilation under glibc-2.1.91 or later should suffice.
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(The kernel distinguishes old and new calls by an IPC_64 flag in
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.IR cmd .)
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.SH "CONFORMING TO"
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SVr4, SVID. SVID does not document the EIDRM error condition.
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.SH "SEE ALSO"
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.BR msgget (2),
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.BR msgrcv (2),
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.BR msgsnd (2),
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.BR ipc (5),
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.BR capabilities (7)
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