.\"	$OpenBSD: shmget.2,v 1.16 2008/04/05 14:56:39 jmc Exp $
.\"	$NetBSD: shmget.2,v 1.2 1997/03/27 08:20:39 mikel Exp $
.\"
.\" Copyright (c) 1995 Frank van der Linden
.\" All rights reserved.
.\"
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.\"    must display the following acknowledgement:
.\"      This product includes software developed for the NetBSD Project
.\"      by Frank van der Linden
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.\"/
.Dd $Mdocdate: April 5 2008 $
.Dt SHMGET 2
.Os
.Sh NAME
.Nm shmget
.Nd get shared memory area identifier
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/ipc.h>
.Fd #include <sys/shm.h>
.Ft int
.Fn shmget "key_t key" "size_t size" "int shmflg"
.Sh DESCRIPTION
.Fn shmget
returns the shared memory identifier associated with the key
.Fa key .
.Pp
A shared memory segment is created if either
.Fa key
is equal to
.Dv IPC_PRIVATE ,
or
.Fa key
does not have a shared memory segment identifier associated with it, and the
.Dv IPC_CREAT
bit is set in
.Fa shmflg .
.Pp
If a new shared memory segment is created, the data structure associated with
it (the
.Va shmid_ds
structure, see
.Xr shmctl 2 )
is initialized as follows:
.Bl -bullet
.It
.Va shm_perm.cuid
and
.Va shm_perm.uid
are set to the effective uid of the calling process.
.It
.Va shm_perm.gid
and
.Va shm_perm.cgid
are set to the effective gid of the calling process.
.It
.Va shm_perm.mode
is set to the lower 9 bits of
.Fa shmflg .
.It
.Va shm_lpid ,
.Va shm_nattch ,
.Va shm_atime ,
and
.Va shm_dtime
are set to 0.
.It
.Va shm_ctime
is set to the current time.
.It
.Va shm_segsz
is set to the value of
.Fa size .
.El
.Sh RETURN VALUES
Upon successful completion a positive shared memory segment identifier is
returned.
Otherwise, \-1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EACCES
A shared memory segment is already associated with
.Fa key
and the caller has no permission to access it.
.It Bq Er EEXIST
Both
.Dv IPC_CREAT
and
.Dv IPC_EXCL
are set in
.Fa shmflg ,
and a shared memory segment is already associated with
.Fa key .
.It Bq Er EINVAL
A shared memory segment is already associated with
.Fa key
and its
.Fa size
is less than the requested size.
.It Bq Er ENOSPC
A new shared memory identifier could not be created because the system limit
for the number of shared memory identifiers has been reached.
.It Bq Er ENOENT
.Dv IPC_CREAT
was not set in
.Fa shmflg
and no shared memory segment associated with
.Fa key
was found.
.It Bq Er ENOMEM
There is not enough memory left to create a shared memory segment of the
requested size.
.El
.Sh SEE ALSO
.Xr ipcrm 1 ,
.Xr ipcs 1 ,
.Xr mmap 2 ,
.Xr shmat 2 ,
.Xr shmctl 2 ,
.Xr ftok 3