SHMCTL(2) INTERACTIVE UNIX System 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 shmid_ds *buf;
DESCRIPTION
The shmctl system call provides a variety of shared memory
control operations as specified by cmd. The following cmds
are available:
IPC_STAT 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}
IPC_SET 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 shm_perm.cuid or
shm_perm.uid in the data structure associated
with shmid.
IPC_RMID Remove the shared memory identifier specified by
shmid from the system and destroy the shared
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 shm_perm.cuid or
shm_perm.uid in the data structure associated
with shmid.
SHM_LOCK 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.
SHM_UNLOCK Unlock the shared memory segment specified by
Rev. C Software Development Set Page 1
SHMCTL(2) INTERACTIVE UNIX System SHMCTL(2)
shmid. This cmd can only be executed by a pro-
cess that has an effective user ID equal to
super-user.
The shmctl system call will fail if one or more of the fol-
lowing is true:
[EINVAL] Shmid is not a valid shared memory identifier.
[EINVAL] Cmd is not a valid command.
[EACCES] Cmd is equal to IPC_STAT and {READ} operation
permission is denied to the calling process [see
intro(2)].
[EPERM] Cmd is equal to IPC_RMID or IPC_SET, and the
effective user ID of the calling process is not
equal to that of super-user or to the value of
shm_perm.cuid or shm_perm.uid in the data struc-
ture associated with shmid.
[EPERM] Cmd is equal to SHM_LOCK or SHM_UNLOCK, 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 SHM_LOCK, and there is not
enough memory.
SEE ALSO
shmget(2), shmop(2).
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Other-
wise, a value of -1 is returned, and errno is set to indi-
cate the error.
NOTES
The user must explicitly remove shared memory segments after
the last reference to them has been removed.
Rev. C Software Development Set Page 2