SHMCTL(2) SHMCTL(2)
NAME
shmctl - shared memory control operations
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
int shmctl (shmid, cmd, buf)
int shmid, cmd;
struct shmidds *buf;
DESCRIPTION
shmctl provides a variety of shared memory control
operations as specified by cmd. The following cmds are
available:
IPCSTAT Place the current value of each member of the
data structure associated with shmid into the
structure pointed to by buf. The contents of
this structure are defined in intro(2). {READ}
IPCSET Set the value of the following members of the
data structure associated with shmid to the
corresponding value found in the structure
pointed to by buf:
shm_perm.uid
shm_perm.gid
shm_perm.mode /* only low 9 bits */
This cmd can only be executed by a process that
has an effective user ID equal to that of super
user, or to the value of shmperm.cuid or
shmperm.uid in the data structure associated
with shmid.
IPCRMID Remove the shared memory identifier specified by
shmid from the system and destroy the shared
Page 1 May 1989
SHMCTL(2) SHMCTL(2)
memory segment and data structure associated with
it. This cmd can only be executed by a process
that has an effective user ID equal to that of
super user, or to the value of shmperm.cuid or
shmperm.uid in the data structure associated
with shmid.
SHMLOCK Lock the shared memory segment specified by shmid
in memory. This cmd can only be executed by a
process that has an effective user ID equal to
super user.
SHMUNLOCK Unlock the shared memory segment specified by
shmid. This cmd can only be executed by a
process that has an effective user ID equal to
super user.
shmctl will fail if one or more of the following are true:
[EINVAL] Shmid is not a valid shared memory identifier.
[EINVAL] Cmd is not a valid command.
[EACCES] Cmd is equal to IPCSTAT and {READ} operation
permission is denied to the calling process [see
intro(2)].
[EPERM] Cmd is equal to IPCRMID or IPCSET and the
effective user ID of the calling process is not
equal to that of super user, or to the value of
shmperm.cuid or shmperm.uid in the data
structure associated with shmid.
[EPERM] Cmd is equal to SHMLOCK or SHMUNLOCK and the
effective user ID of the calling process is not
equal to that of super user.
[EFAULT] Buf points to an illegal address.
[ENOMEM] Cmd is equal to SHMLOCK and there is not enough
Page 2 May 1989
SHMCTL(2) SHMCTL(2)
memory.
SEE ALSO
shmget(2), shmop(2).
DIAGNOSTICS
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and errno is set to
indicate the error.
NOTES
The user must explicitly remove shared memory segments after
the last reference to them has been removed.
Page 3 May 1989