2 .\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>
4 .\" All rights reserved.
6 .\" Redistribution and use in source and binary forms, with or without
7 .\" modification, are permitted provided that the following conditions
9 .\" 1. Redistributions of source code must retain the above copyright
10 .\" notice, this list of conditions and the following disclaimer.
11 .\" 2. Redistributions in binary form must reproduce the above copyright
12 .\" notice, this list of conditions and the following disclaimer in the
13 .\" documentation and/or other materials provided with the distribution.
15 .\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
16 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 .\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
19 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 .\" $FreeBSD: src/lib/libc/sys/shmget.2,v 1.8.2.6 2001/12/14 18:34:01 ru Exp $
33 .Nd obtain a shared memory identifier
42 .Fn shmget "key_t key" "size_t size" "int flag"
44 Based on the values of
49 returns the identifier of a newly created or previously existing shared
52 .\" The following bit about keys and modes also applies to semaphores
53 .\" and message queues.
56 is analogous to a filename: it provides a handle that names an
57 IPC object. There are three ways to specify a key:
60 IPC_PRIVATE may be specified, in which case a new IPC object
63 An integer constant may be specified. If no IPC object corresponding
66 is specified and the IPC_CREAT bit is set in
68 a new one will be created.
71 may be used to generate a key from a pathname. See
75 The mode of a newly created IPC object is determined by
77 the following constants into the
80 .Bl -tag -width XSHM_WXX6XXX
84 Write access for user.
86 Read access for group.
88 Write access for group.
90 Read access for other.
92 Write access for other.
95 .\" XXX - we should also mention how uid, euid, and gid affect ownership
98 .\" end section about keys and modes
101 When creating a new shared memory segment,
103 indicates the desired size of the new segment in bytes. The size
104 of the segment may be rounded up to a multiple convenient to the
105 kernel (i.e., the page size).
107 Upon successful completion,
109 returns the positive integer identifier of a shared memory segment.
110 Otherwise, -1 is returned and
112 set to indicate the error.
118 .\" XXX What about ipcperm failing?
121 Size specified is greater than the size of the previously existing segment.
122 Size specified is less than the system imposed minimum, or greater than
123 the system imposed maximum.
125 No shared memory segment was found matching
127 and IPC_CREAT was not specified.
129 The kernel was unable to allocate enough memory to
132 IPC_CREAT and IPC_EXCL were specified, and a shared memory segment