175 lines
4.5 KiB
Groff
175 lines
4.5 KiB
Groff
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.\" $NetBSD: shmget.2,v 1.22 2008/10/27 16:49:10 wiz 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 October 27, 2008
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.Dt SHMGET 2
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.Os
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.Sh NAME
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.Nm shmget
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.Nd get shared memory segment
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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 shmget "key_t key" "size_t size" "int shmflg"
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.Sh DESCRIPTION
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.Fn shmget
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returns the shared memory identifier associated with the key
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.Fa key .
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.Pp
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A shared memory segment is created if either
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.Fa key
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is equal to
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.Dv IPC_PRIVATE ,
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or
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.Fa key
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does not have a shared memory segment identifier associated with it, and the
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.Dv IPC_CREAT
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bit is set in
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.Fa shmflg .
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If both the
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.Dv IPC_CREAT
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bit and the
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.Dv IPC_EXCL
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bit are set in
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.Fa shmflg ,
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and
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.Fa key
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has a shared memory segment identifier associated with it already,
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the operation will fail.
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.Pp
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If a new shared memory segment is created, the data structure
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associated with it (the
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.Va shmid_ds
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structure, see
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.Xr shmctl 2 )
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is initialized as follows:
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.Bl -bullet
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.It
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.Va shm_perm.cuid
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and
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.Va shm_perm.uid
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are set to the effective uid of the calling process.
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.It
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.Va shm_perm.gid
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and
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.Va shm_perm.cgid
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are set to the effective gid of the calling process.
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.It
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.Va shm_perm.mode
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is set to the lower 9 bits of
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.Fa shmflg .
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.It
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.Va shm_lpid ,
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.Va shm_nattch ,
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.Va shm_atime ,
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and
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.Va shm_dtime
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are set to 0.
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.It
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.Va shm_ctime
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is set to the current time.
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.It
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.Va shm_segsz
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is set to the value of
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.Fa size .
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.El
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.Sh RETURN VALUES
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Upon successful completion a positive shared memory segment identifier
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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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.Bl -tag -width Er
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.It Bq Er EACCES
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A shared memory segment is already associated with
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.Fa key
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and the caller has no permission to access it.
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.It Bq Er EEXIST
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Both
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.Dv IPC_CREAT
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and
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.Dv IPC_EXCL
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are set in
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.Fa shmflg ,
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and a shared memory segment is already associated with
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.Fa key .
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.It Bq Er EINVAL
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No shared memory segment is to be created, and a shared memory segment
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exists for
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.Fa key ,
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but the size of the segment associated with it is less
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than
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.Fa size ,
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which is non-zero.
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.Pp
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A shared memory segment
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.Em is
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to be created, and
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.Fa size
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is less than the system imposed minimum, or greater than the system
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imposed maximum (refer to the
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.Li kern.ipc
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values in
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.Xr sysctl 7 ) .
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.It Bq Er ENOENT
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.Dv IPC_CREAT
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is not set in
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.Fa shmflg
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and no shared memory segment associated with
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.Fa key
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was found.
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.It Bq Er ENOMEM
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There is not enough memory left to create a shared memory segment of the
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requested size.
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.It Bq Er ENOSPC
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A new shared memory identifier could not be created because the system limit
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for the number of shared memory identifiers has been reached.
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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 mmap 2 ,
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.Xr shmat 2 ,
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.Xr shmctl 2 ,
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.Xr ftok 3 ,
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.Xr sysctl 7
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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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