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	1	.\" $OpenBSD: shmget.2,v 1.2 1996/10/08 01:20:16 michaels Exp $
	2	.\" $NetBSD: shmget.2,v 1.1 1995/10/16 23:49:32 jtc Exp $
	3	.\"
	4	.\" Copyright (c) 1995 Frank van der Linden
	5	.\" All rights reserved.
	6	.\"
	7	.\" Redistribution and use in source and binary forms, with or without
	8	.\" modification, are permitted provided that the following conditions
	9	.\" are met:
	10	.\" 1. Redistributions of source code must retain the above copyright
	11	.\" notice, this list of conditions and the following disclaimer.
	12	.\" 2. Redistributions in binary form must reproduce the above copyright
	13	.\" notice, this list of conditions and the following disclaimer in the
	14	.\" documentation and/or other materials provided with the distribution.
	15	.\" 3. All advertising materials mentioning features or use of this software
	16	.\" must display the following acknowledgement:
	17	.\" This product includes software developed for the NetBSD Project
	18	.\" by Frank van der Linden
	19	.\" 4. The name of the author may not be used to endorse or promote products
	20	.\" derived from this software without specific prior written permission
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
	23	.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	24	.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
	25	.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
	26	.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	27	.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	28	.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	29	.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	30	.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	31	.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	32	.\"/
	33	.Dd August 17, 1995
	34	.Dt SHMGET 2
	35	.Os
	36	.Sh NAME
	37	.Nm shmget
	38	.Nd get shared memory area identifier
	39	.Sh SYNOPSIS
	40	.Fd #include <sys/shm.h>
	41	.Ft int
	42	.Fo shmget
	43	.Fa "key_t key"
	44	.Fa "size_t size"
	45	.Fa "int shmflg"
	46	.Fc
	47	.Sh DESCRIPTION
	48	.Fn shmget
	49	returns the shared memory identifier associated with the key
	50	.Fa key .
	51	.Pp
	52	A shared memory segment is created if either
	53	.Fa key
	54	is equal to IPC_PRIVATE, or
	55	.Fa key
	56	does not have a shared memory segment identifier associated with it, and the IPC_CREAT
	57	bit is set in
	58	.Fa shmflg.
	59	.Pp
	60	If a new shared memory segment is created, the data structure associated with it (the
	61	.Va shmid_ds
	62	structure, see
	63	.Xr shmctl 2 )
	64	is initialized as follows:
	65	.Bl -bullet
	66	.It
	67	.Va shm_perm.cuid
	68	and
	69	.Va shm_perm.uid
	70	are set to the effective uid of the calling process.
	71	.It
	72	.Va shm_perm.gid
	73	and
	74	.Va shm_perm.cgid
	75	are set to the effective gid of the calling process.
	76	.It
	77	.Va shm_perm.mode
	78	is set to the lower 9 bits of
	79	.Fa shmflg .
	80	.It
	81	.Va shm_lpid ,
	82	.Va shm_nattch ,
	83	.Va shm_atime ,
	84	and
	85	.Va shm_dtime
	86	are set to 0
	87	.It
	88	.Va shm_ctime
	89	is set to the current time.
	90	.It
	91	.Va shm_segsz
	92	is set to the value of
	93	.Fa size .
	94	.It
	95	The
	96	.Xr ftok 3
	97	function may be used to generate a key from a pathname.
	98	.El
	99	.Sh RETURN VALUES
	100	Upon successful completion a positive shared memory segment identifier is returned.
	101	Otherwise, -1 is returned and the global variable
	102	.Va errno
	103	is set to indicate the error.
	104	.Sh ERRORS
	105	The
	106	.Fn shmget
	107	system call will fail if:
	108	.Bl -tag -width Er
	109	.\" ===========
	110	.It Bq Er EACCES
	111	A shared memory segment is already associated with
	112	.Fa key
	113	and the caller has no permission to access it.
	114	.\" ===========
	115	.It Bq Er EEXIST
	116	Both IPC_CREAT and IPC_EXCL are set in
	117	.Fa shmflg ,
	118	and a shared memory segment is already associated with
	119	.Fa key .
	120	.\" ===========
	121	.It Bq Er EINVAL
	122	No shared memory segment is to be created,
	123	and a shared memory segment exists for
	124	.Fa key ,
	125	but the size of the segment associated with it
	126	is less than
	127	.Fa size ,
	128	which is non-zero.
	129	.\" ===========
	130	.It Bq Er ENOENT
	131	IPC_CREAT was not set in
	132	.Fa shmflg
	133	and no shared memory segment associated with
	134	.Fa key
	135	was found.
	136	.\" ===========
	137	.It Bq Er ENOMEM
	138	There is not enough memory left to created a shared memory segment of the
	139	requested size.
	140	.\" ===========
	141	.It Bq Er ENOSPC
	142	A new shared memory identifier could not be created because the system limit
	143	for the number of shared memory identifiers has been reached.
	144	.El
	145	.Sh LEGACY SYNOPSIS
	146	.Fd #include <sys/types.h>
	147	.Fd #include <sys/ipc.h>
	148	.Fd #include <sys/shm.h>
	149	.Pp
	150	.Ft int
	151	.br
	152	.Fo shmget
	153	.Fa "key_t key"
	154	.Fa "int size"
	155	.Fa "int shmflg"
	156	.Fc ;
	157	.Pp
	158	All of these include files are necessary.
	159	The type of
	160	.Fa size
	161	has changed.
	162	.Sh SEE ALSO
	163	.Xr ftok 3 ,
	164	.Xr shmat 2 ,
	165	.Xr shmctl 2 ,
	166	.Xr shmdt 2 ,
	167	.Xr compat 5