shmctl(2)							System Calls Manual							 shmctl(2)

Name
       shmctl - shared memory control operations

Syntax
       #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 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

       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 either that of the superuser or to the
		       value of 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 struc-
		      ture  associated	with  it. This cmd can only be executed by a process that has an effective user ID equal to either that of
		      the superuser or to the value of in the data structure associated with shmid.

       SHM_LOCK       Lock the shared memory segment specified by shmid in memory.  Lock prevents the shared memory segment from being swapped	or
		      paged.  This cmd can only be executed by a process that has an effective user ID equal to the superuser.

       SHM_UNLOCK     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 the superuser.

Return Values
       Upon successful completion, a value of zero (0) is returned.  Otherwise, a value of -1 is returned, and	errno  is  set	to  indicated  the
       error.

Diagnostics
       The system call fails if any of the following is true:

       [EINVAL]       The shmid is not a valid shared memory identifier.

       [EINVAL]       The cmd is not a valid command.

       [EACCES]       The cmd is equal to IPC_STAT, and read permission is denied to the calling process.  For further information, see

       [EPERM]	      The  cmd is equal to IPC_RMID or IPC_SET, and the effective user ID of the calling process is not equal to that of the supe-
		      ruser or to the value of in the data structure associated with shmid.

       [EPERM]	      The cmd is equal to SHM_LOCK or SHM_UNLOCK and the effective user ID of the calling process is not  equal  to  that  of  the
		      superuser.

       [EINVAL]       The cmd is equal to SHM_LOCK, and the shared memory segment is currently locked by this process.

       [EINVAL]       The  cmd	is equal to SHM_UNLOCK, and the shared memory segment specified by shmid is not currently locked in memory by this
		      process.

       [EFAULT]       The buf points to an illegal address.

See Also
       shmget(2), shmop(2)

																	 shmctl(2)