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/shmctl.2,v 1.9.2.4 2001/12/14 18:34:01 ru Exp $
28 .Dd September 12, 2019
33 .Nd shared memory control
42 .Fn shmctl "int shmid" "int cmd" "struct shmid_ds *buf"
44 Performs the action specified by
46 on the shared memory segment identified by
48 .Bl -tag -width SHM_UNLOCKX
51 .Fa "struct shmid_ds" ,
52 storing it in the memory pointed to by
55 .\" XXX need to make sure that this is correct for FreeBSD
63 members of the segment's
65 to match those of the struct pointed to by
67 The calling process's effective uid must
72 or it must have superuser privileges.
74 Removes the segment from the system.
75 The removal will not take
76 effect until all processes having attached the segment have exited;
79 operation has taken place, no further
80 processes will be allowed to attach the segment.
82 to succeed, the calling process's effective uid must match
86 or the process must have superuser privileges.
88 .\" Locks the segment in memory.
89 .\" The calling process must have superuser privileges.
90 .\" Not implemented in FreeBSD.
92 .\" Unlocks the segment from memory.
93 .\" The calling process must have superuser privileges.
94 .\" Not implemented in FreeBSD.
99 struct is defined as follows:
101 .\" I fiddled with the spaces a bit to make it fit well when viewed
102 .\" with nroff, but otherwise it's straight from sys/shm.h
105 typedef unsigned int shmatt_t;
108 struct ipc_perm shm_perm; /* operation permission structure */
109 size_t shm_segsz; /* size of segment in bytes */
110 pid_t shm_lpid; /* process ID of last shared memory op */
111 pid_t shm_cpid; /* process ID of creator */
112 shmatt_t shm_nattch; /* number of current attaches */
113 time_t shm_atime; /* time of last shmat() */
114 time_t shm_dtime; /* time of last shmdt() */
115 time_t shm_ctime; /* time of last change by shmctl() */
116 void *shm_internal; /* sysv stupidity */
122 structure used inside the
124 structure is defined in
129 The XSI Interprocess Communication family of functions is also available
130 as an implementation in userspace.
133 daemon has to be running.
137 variable is set in a process' environment, the process and its children
138 will use the userspace implementation.
144 Invalid operation, or
145 no shared memory segment was found corresponding to
148 .\" XXX I think the following is right: ipcperm() only returns EPERM
149 .\" when an attempt is made to modify (IPC_M) by a non-creator
152 The calling process's effective uid does not match the uid of
153 the shared memory segment's owner or creator.
155 Permission denied due to mismatch between operation and mode of
156 shared memory segment.
167 specific userspace implementation (see