230 lines
6.8 KiB
Groff
230 lines
6.8 KiB
Groff
.\" $OpenBSD: shmctl.2,v 1.2 1996/10/08 01:20:15 michaels Exp $
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.\" $NetBSD: shmctl.2,v 1.1 1995/10/16 23:49:30 jtc 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 August 17, 1995
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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 SYNOPSIS
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.Fd #include <sys/shm.h>
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.Ft int
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.Fo shmctl
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.Fa "int shmid"
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.Fa "int cmd"
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.Fa "struct shmid_ds *buf"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn shmctl
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system call performs some control operations on the shared memory area
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specified by
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.Fa shmid .
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Each shared memory segment has a data structure associated with it,
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parts of which may be altered by
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.Fn shmctl
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and parts of which determine the actions of
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.Fn shmctl .
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This structure is defined as follows in
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.Aq Pa sys/shm.h :
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.Bd -literal
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struct shmid_ds {
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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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short 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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void *shm_internal; /* sysv stupidity */
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};
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.Ed
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.Pp
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The
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.Bf -literal
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ipc_perm
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.Ef
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structure used inside the
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.Bf -literal
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shmid_ds
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.Ef
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structure is defined in
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.Aq Pa sys/ipc.h
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and looks like this:
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.Bd -literal
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struct ipc_perm {
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uid_t uid; /* Owner's user ID */
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gid_t gid; /* Owner's group ID */
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uid_t cuid; /* Creator's user ID */
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gid_t cgid; /* Creator's group ID */
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mode_t mode; /* r/w permission (see chmod(2)) */
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unsigned short _seq; /* Reserved for internal use */
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key_t _key; /* Reserved for internal use */
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};
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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. Only the super-user or a process
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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 queue can do this.
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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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.\" ===========
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.It Bq Er EACCES
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The command is IPC_STAT
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and the caller has no read permission for this shared memory segment.
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.\" ===========
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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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.\" ===========
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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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.Va cmd
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is not a valid command.
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.\" ===========
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.It Bq Er EPERM
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.Fa cmd
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is equal to IPC_SET or IPC_RMID and the caller is not the super-user,\
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nor does 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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An attempt is made to increase the value of
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.Va shm_qbytes
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through IPC_SET
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but the caller is not the super-user.
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.El
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.Sh LEGACY SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/ipc.h>
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.Fd #include <sys/shm.h>
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.Pp
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All of these include files are necessary.
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.Sh LEGACY DESCRIPTION
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The
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.Bf -literal
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ipc_perm
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.Ef
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structure used inside the
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.Bf -literal
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shmid_ds
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.Ef
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structure, as defined in
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.Aq Pa sys/ipc.h ,
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looks like this:
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.Bd -literal
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struct ipc_perm {
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__uint16_t cuid; /* Creator's user id */
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__uint16_t cgid; /* Creator's group id */
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__uint16_t uid; /* Owner's user id */
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__uint16_t gid; /* Owner's group id */
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mode_t mode; /* r/w permission (see chmod(2)) */
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__uint16_t seq; /* Reserved for internal use */
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key_t key; /* Reserved for internal use */
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};
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.Ed
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.Pp
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This structure is maintained for binary backward compatibility
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with previous versions of the interface.
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New code should not use this interface,
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because ID values may be truncated.
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.Pp
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Specifically,
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LEGACY mode limits the allowable uid/gid ranges to 0-32767.
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If the user has a UID that is out of this range (e.g., "nobody"),
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software using the LEGACY API will not behave as expected.
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.Sh SEE ALSO
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.Xr shmat 2 ,
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.Xr shmdt 2 ,
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.Xr shmget 2 ,
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.Xr compat 5
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