SHMCTL(2)                            SysV                            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
     shmctl 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.

ERRORS
     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 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
                structure 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. Otherwise, a value
     of -1 is returned and errno is set to indicate the error.

NOTES
     The following cmds, available on some other implementations, are not
     implemented under Domain/OS SysV.

     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 shmid.  This
                 cmd can only be executed by a process that has an effective
                 user ID equal to super-user.

     The user must explicitly remove shared memory segments after the last
     reference to them has been removed.