1.\" 2.\" Copyright (c) 1995 David Hovemeyer <[email protected]> 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.\" $FreeBSD$ 27.\" 28.Dd July 17, 1995 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 IPC_RMID operation has taken place, no further 78processes will be allowed to attach the segment. 79For the operation 80to succeed, the calling process's effective uid must match 81.Fa shm_perm.uid 82or 83.Fa shm_perm.cuid , 84or the process must have superuser privileges. 85.\" .It Dv SHM_LOCK 86.\" Locks the segment in memory. The calling process must have 87.\" superuser privileges. Not implemented in FreeBSD. 88.\" .It Dv SHM_UNLOCK 89.\" Unlocks the segment from memory. The calling process must 90.\" have superuser privileges. Not implemented in FreeBSD. 91.El 92.Pp 93The 94.Vt shmid_ds 95structure is defined as follows: 96.\" 97.\" I fiddled with the spaces a bit to make it fit well when viewed 98.\" with nroff, but otherwise it's straight from sys/shm.h 99.\" 100.Bd -literal 101struct shmid_ds { 102 struct ipc_perm shm_perm; /* operation permission structure */ 103 int shm_segsz; /* size of segment in bytes */ 104 pid_t shm_lpid; /* process ID of last shared memory op */ 105 pid_t shm_cpid; /* process ID of creator */ 106 short shm_nattch; /* number of current attaches */ 107 time_t shm_atime; /* time of last shmat() */ 108 time_t shm_dtime; /* time of last shmdt() */ 109 time_t shm_ctime; /* time of last change by shmctl() */ 110 void *shm_internal; /* sysv stupidity */ 111}; 112.Ed 113.Sh RETURN VALUES 114.Rv -std shmctl 115.Sh ERRORS 116The 117.Fn shmctl 118system call 119will fail if: 120.Bl -tag -width Er 121.It Bq Er EINVAL 122Invalid operation, or 123no shared memory segment was found corresponding to 124.Fa shmid . 125.\" 126.\" XXX I think the following is right: ipcperm() only returns EPERM 127.\" when an attempt is made to modify (IPC_M) by a non-creator 128.\" non-owner 129.It Bq Er EPERM 130The calling process's effective uid does not match the uid of 131the shared memory segment's owner or creator. 132.It Bq Er EACCES 133Permission denied due to mismatch between operation and mode of 134shared memory segment. 135.El 136.Sh "SEE ALSO" 137.Xr shmat 2 , 138.Xr shmdt 2 , 139.Xr shmget 2 , 140.Xr ftok 3 141