210 lines
5.8 KiB
Groff
210 lines
5.8 KiB
Groff
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.\" $NetBSD: shmctl.2,v 1.21 2010/03/22 19:30:55 joerg Exp $
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.\"
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.\" Copyright (c) 1995 Frank van der Linden
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project
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.\" by Frank van der Linden
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd November 25, 2006
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.Dt SHMCTL 2
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.Os
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.Sh NAME
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.Nm shmctl
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.Nd shared memory control operations
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/shm.h
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.Ft int
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.Fn shmctl "int shmid" "int cmd" "struct shmid_ds *buf"
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.Sh DESCRIPTION
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The
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.Fn shmctl
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system call performs control operations on the shared memory segment
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specified by
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.Fa shmid .
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.Pp
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Each shared memory segment has a
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.Sy shmid_ds
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structure associated with it which contains the following members:
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.Bd -literal
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struct ipc_perm shm_perm; /* operation permissions */
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size_t shm_segsz; /* size of segment in bytes */
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pid_t shm_lpid; /* pid of last shm op */
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pid_t shm_cpid; /* pid of creator */
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shmatt_t shm_nattch; /* # of current attaches */
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time_t shm_atime; /* last shmat() time */
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time_t shm_dtime; /* last shmdt() time */
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time_t shm_ctime; /* last change by shmctl() */
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.Ed
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.Pp
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The
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.Sy ipc_perm
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structure used inside the
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.Sy shmid_ds
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structure is defined in
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.In sys/ipc.h
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and contains the following members:
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.Bd -literal
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uid_t cuid; /* creator user id */
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gid_t cgid; /* creator group id */
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uid_t uid; /* user id */
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gid_t gid; /* group id */
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mode_t mode; /* permission (lower 9 bits) */
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.Ed
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.Pp
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The operation to be performed by
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.Fn shmctl
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is specified in
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.Fa cmd
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and is one of:
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.Bl -tag -width IPC_RMIDX
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.It Dv IPC_STAT
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Gather information about the shared memory segment and place it in the
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structure pointed to by
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.Fa buf .
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.It Dv IPC_SET
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Set the value of the
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.Va shm_perm.uid ,
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.Va shm_perm.gid
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and
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.Va shm_perm.mode
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fields in the structure associated with
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.Fa shmid .
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The values are taken from the corresponding fields in the structure
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pointed to by
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.Fa buf .
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This operation can only be executed by the super-user, or a process that
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has an effective user id equal to either
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.Va shm_perm.cuid
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or
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.Va shm_perm.uid
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in the data structure associated with the shared memory segment.
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.It Dv IPC_RMID
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Remove the shared memory segment specified by
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.Fa shmid
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and destroy the data associated with it.
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Only the super-user or a process with an effective uid equal to the
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.Va shm_perm.cuid
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or
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.Va shm_perm.uid
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values in the data structure associated with the segment can do this.
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.It Dv SHM_LOCK
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Lock the shared memory segment specified by
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.Fa shmid
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in memory.
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This operation can only be executed by the super-user.
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.It Dv SHM_UNLOCK
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Unlock the shared memory segment specified by
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.Fa shmid .
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This operation can only be executed by the super-user.
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.El
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.Pp
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The read and write permissions on a shared memory identifier
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are determined by the
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.Va shm_perm.mode
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field in the same way as is
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done with files (see
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.Xr chmod 2 ) ,
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but the effective uid can match either the
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.Va shm_perm.cuid
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field or the
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.Va shm_perm.uid
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field, and the
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effective gid can match either
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.Va shm_perm.cgid
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or
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.Va shm_perm.gid .
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.Sh RETURN VALUES
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Upon successful completion, a value of 0 is returned.
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Otherwise, \-1 is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn shmctl
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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The command is
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.Dv IPC_STAT
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and the caller has no read permission for this shared memory segment.
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.It Bq Er EFAULT
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.Fa buf
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specifies an invalid address.
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.It Bq Er EINVAL
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.Fa shmid
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is not a valid shared memory segment identifier.
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.Pp
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.Va cmd
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is not a valid command.
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.It Bq Er ENOMEM
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The
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.Fa cmd
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is equal to
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.Dv SHM_LOCK
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and there is not enough physical memory.
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.It Bq Er EPERM
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.Fa cmd
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is equal to
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.Dv IPC_SET
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or
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.Dv IPC_RMID
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and the caller is not the super-user, nor does
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the effective uid match either the
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.Va shm_perm.uid
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or
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.Va shm_perm.cuid
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fields of the data structure associated with the shared memory segment.
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.Pp
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An attempt was made to increase the value of
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.Va shm_qbytes
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through
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.Dv IPC_SET
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but the caller is not the super-user.
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.Pp
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The
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.Fa cmd
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is equal to
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.Dv SHM_LOCK
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or
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.Dv SHM_UNLOCK
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and the caller is not the super-user.
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.El
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.Sh SEE ALSO
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.Xr ipcrm 1 ,
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.Xr ipcs 1 ,
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.Xr shmat 2 ,
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.Xr shmget 2
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.Sh STANDARDS
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The
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.Nm
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system call conforms to
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.St -xsh5 .
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.Sh HISTORY
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Shared memory segments appeared in the first release of
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.At V .
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