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authorJacob McDonnell <jacob@jacobmcdonnell.com>2026-04-25 19:55:15 -0400
committerJacob McDonnell <jacob@jacobmcdonnell.com>2026-04-25 19:55:15 -0400
commit253e67c8b3a72b3a4757fdbc5845297628db0a4a (patch)
treeadf53b66087aa30dfbf8bf391a1dadb044c3bf4d /static/netbsd/man2/shmctl.2
parenta9157ce950dfe2fc30795d43b9d79b9d1bffc48b (diff)
docs: Added All NetBSD Manuals
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+.\" $NetBSD: shmctl.2,v 1.22 2026/01/02 22:22:22 nia Exp $
+.\"
+.\" Copyright (c) 1995 Frank van der Linden
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\" notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\" notice, this list of conditions and the following disclaimer in the
+.\" documentation and/or other materials provided with the distribution.
+.\" 3. The name of the author may not be used to endorse or promote products
+.\" derived from this software without specific prior written permission
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.Dd November 25, 2006
+.Dt SHMCTL 2
+.Os
+.Sh NAME
+.Nm shmctl
+.Nd shared memory control operations
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In sys/shm.h
+.Ft int
+.Fn shmctl "int shmid" "int cmd" "struct shmid_ds *buf"
+.Sh DESCRIPTION
+The
+.Fn shmctl
+system call performs control operations on the shared memory segment
+specified by
+.Fa shmid .
+.Pp
+Each shared memory segment has a
+.Sy shmid_ds
+structure associated with it which contains the following members:
+.Bd -literal
+ struct ipc_perm shm_perm; /* operation permissions */
+ size_t shm_segsz; /* size of segment in bytes */
+ pid_t shm_lpid; /* pid of last shm op */
+ pid_t shm_cpid; /* pid of creator */
+ shmatt_t shm_nattch; /* # of current attaches */
+ time_t shm_atime; /* last shmat() time */
+ time_t shm_dtime; /* last shmdt() time */
+ time_t shm_ctime; /* last change by shmctl() */
+.Ed
+.Pp
+The
+.Sy ipc_perm
+structure used inside the
+.Sy shmid_ds
+structure is defined in
+.In sys/ipc.h
+and contains the following members:
+.Bd -literal
+ uid_t cuid; /* creator user id */
+ gid_t cgid; /* creator group id */
+ uid_t uid; /* user id */
+ gid_t gid; /* group id */
+ mode_t mode; /* permission (lower 9 bits) */
+.Ed
+.Pp
+The operation to be performed by
+.Fn shmctl
+is specified in
+.Fa cmd
+and is one of:
+.Bl -tag -width IPC_RMIDX
+.It Dv IPC_STAT
+Gather information about the shared memory segment and place it in the
+structure pointed to by
+.Fa buf .
+.It Dv IPC_SET
+Set the value of the
+.Va shm_perm.uid ,
+.Va shm_perm.gid
+and
+.Va shm_perm.mode
+fields in the structure associated with
+.Fa shmid .
+The values are taken from the corresponding fields in the structure
+pointed to by
+.Fa buf .
+This operation can only be executed by the super-user, or a process that
+has an effective user id equal to either
+.Va shm_perm.cuid
+or
+.Va shm_perm.uid
+in the data structure associated with the shared memory segment.
+.It Dv IPC_RMID
+Remove the shared memory segment specified by
+.Fa shmid
+and destroy the data associated with it.
+Only the super-user or a process with an effective uid equal to the
+.Va shm_perm.cuid
+or
+.Va shm_perm.uid
+values in the data structure associated with the segment can do this.
+.It Dv SHM_LOCK
+Lock the shared memory segment specified by
+.Fa shmid
+in memory.
+This operation can only be executed by the super-user.
+.It Dv SHM_UNLOCK
+Unlock the shared memory segment specified by
+.Fa shmid .
+This operation can only be executed by the super-user.
+.El
+.Pp
+The read and write permissions on a shared memory identifier
+are determined by the
+.Va shm_perm.mode
+field in the same way as is
+done with files (see
+.Xr chmod 2 ) ,
+but the effective uid can match either the
+.Va shm_perm.cuid
+field or the
+.Va shm_perm.uid
+field, and the
+effective gid can match either
+.Va shm_perm.cgid
+or
+.Va shm_perm.gid .
+.Sh RETURN VALUES
+Upon successful completion, a value of 0 is returned.
+Otherwise, \-1 is returned and the global variable
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+.Fn shmctl
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EACCES
+The command is
+.Dv IPC_STAT
+and the caller has no read permission for this shared memory segment.
+.It Bq Er EFAULT
+.Fa buf
+specifies an invalid address.
+.It Bq Er EINVAL
+.Fa shmid
+is not a valid shared memory segment identifier.
+.Pp
+.Va cmd
+is not a valid command.
+.It Bq Er ENOMEM
+The
+.Fa cmd
+is equal to
+.Dv SHM_LOCK
+and there is not enough physical memory.
+.It Bq Er EPERM
+.Fa cmd
+is equal to
+.Dv IPC_SET
+or
+.Dv IPC_RMID
+and the caller is not the super-user, nor does
+the effective uid match either the
+.Va shm_perm.uid
+or
+.Va shm_perm.cuid
+fields of the data structure associated with the shared memory segment.
+.Pp
+An attempt was made to increase the value of
+.Va shm_qbytes
+through
+.Dv IPC_SET
+but the caller is not the super-user.
+.Pp
+The
+.Fa cmd
+is equal to
+.Dv SHM_LOCK
+or
+.Dv SHM_UNLOCK
+and the caller is not the super-user.
+.El
+.Sh SEE ALSO
+.Xr ipcrm 1 ,
+.Xr ipcs 1 ,
+.Xr shmat 2 ,
+.Xr shmget 2
+.Sh STANDARDS
+The
+.Nm
+system call conforms to
+.St -xsh5 .
+.Sh HISTORY
+Shared memory segments appeared in the first release of
+.At V .