1.\" 2.\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com> 3.\" 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 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. 14.\" 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. 25.\" 26.\" $FreeBSD: src/lib/libc/sys/shmctl.2,v 1.9.2.4 2001/12/14 18:34:01 ru Exp $ 27.\" 28.Dd September 12, 2019 29.Dt SHMCTL 2 30.Os 31.Sh NAME 32.Nm shmctl 33.Nd shared memory control 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In machine/param.h 38.In sys/types.h 39.In sys/ipc.h 40.In sys/shm.h 41.Ft int 42.Fn shmctl "int shmid" "int cmd" "struct shmid_ds *buf" 43.Sh DESCRIPTION 44Performs the action specified by 45.Fa cmd 46on the shared memory segment identified by 47.Fa shmid : 48.Bl -tag -width SHM_UNLOCKX 49.It Dv IPC_STAT 50Fetch the segment's 51.Fa "struct shmid_ds" , 52storing it in the memory pointed to by 53.Fa buf . 54.\" 55.\" XXX need to make sure that this is correct for FreeBSD 56.\" 57.It Dv IPC_SET 58Changes the 59.Fa shm_perm.uid , 60.Fa shm_perm.gid , 61and 62.Fa shm_perm.mode 63members of the segment's 64.Fa "struct shmid_ds" 65to match those of the struct pointed to by 66.Fa buf . 67The calling process's effective uid must 68match either 69.Fa shm_perm.uid 70or 71.Fa shm_perm.cuid , 72or it must have superuser privileges. 73.It Dv IPC_RMID 74Removes the segment from the system. 75The removal will not take 76effect until all processes having attached the segment have exited; 77however, once the 78.Dv IPC_RMID 79operation has taken place, no further 80processes will be allowed to attach the segment. 81For the operation 82to succeed, the calling process's effective uid must match 83.Fa shm_perm.uid 84or 85.Fa shm_perm.cuid , 86or the process must have superuser privileges. 87.\" .It Dv SHM_LOCK 88.\" Locks the segment in memory. 89.\" The calling process must have superuser privileges. 90.\" Not implemented in FreeBSD. 91.\" .It Dv SHM_UNLOCK 92.\" Unlocks the segment from memory. 93.\" The calling process must have superuser privileges. 94.\" Not implemented in FreeBSD. 95.El 96.Pp 97The 98.Fa shmid_ds 99struct is defined as follows: 100.\" 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 103.\" 104.Bd -literal 105typedef unsigned int shmatt_t; 106 107struct shmid_ds { 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 */ 117}; 118.Ed 119.Pp 120The 121.Vt ipc_perm 122structure used inside the 123.Vt shmid_ds 124structure is defined in 125.In sys/ipc.h . 126.Sh RETURN VALUES 127.Rv -std shmctl 128.Sh ENVIRONMENT 129The XSI Interprocess Communication family of functions is also available 130as an implementation in userspace. 131To use it, the 132.Xr sysvipcd 8 133daemon has to be running. 134.Pp 135If the 136.Ev USR_SYSVIPC 137variable is set in a process' environment, the process and its children 138will use the userspace implementation. 139.Sh ERRORS 140.Fn Shmctl 141will fail if: 142.Bl -tag -width Er 143.It Bq Er EINVAL 144Invalid operation, or 145no shared memory segment was found corresponding to 146.Fa shmid . 147.\" 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 150.\" non-owner 151.It Bq Er EPERM 152The calling process's effective uid does not match the uid of 153the shared memory segment's owner or creator. 154.It Bq Er EACCES 155Permission denied due to mismatch between operation and mode of 156shared memory segment. 157.El 158.Sh "SEE ALSO" 159.Xr shmat 2 , 160.Xr shmdt 2 , 161.Xr shmget 2 , 162.Xr ftok 3 163.Sh AUTHORS 164.An -nosplit 165The 166.Dx 167specific userspace implementation (see 168.Sx ENVIRONMENT ) 169was written by 170.An Larisa Grigore . 171