shmctl(2)                                                     shmctl(2)

  shmctl()

  NAME

    shmctl() - control shared memory operations

  SYNOPSIS

    #include 

    int shmctl(int shmid, int cmd, struct shmid_ds *buf)

  DESCRIPTION

    The shmctl(2) function gives you access to the data information associated
    with a shared memory segment, either to read or set the values of members,
    or to remove a shared memory identifier. argument.

    The function parameters are:

    shmid
        An identifier for the shared memory segment. The shared memory segment
        has a shmid_ds data structure associated with it; see  for
        a description of the structure.

    cmd
        The operation to be performed. The following are valid (defined in
        ):

        IPC_STAT
            Copies the current values of the shmid_ds data structure
            associated with shmid into buf.

        IPC_SET
            Sets the value of members of the shmid_ds data structure
            associated with shmid from the same members in buf. The members
            copied are sh_perm.uid sh_perm.gid and the low-order nine bits of
            shm_perm.mode

        IPC_RMID
            Removes the identifier specified by shmid from the system and
            destroys the shared memory segment and data structure associated
            with it.

    buf
        The buffer used to store information copied or to be copied.

    The header file  includes .

  RETURN VALUE

    The shmctl(2) call returns 0 on success. On failure, it returns -1 and
    sets errno

  ERRORS

    The shmctl(2) function can fail for the following reasons:

    [EACCES]
        The cmd is IPC_STAT and the calling process doesn't have read
        permission.

    [EINVAL]
        Shmid is not a valid shared memory identifier.

    [ENOSYS]
        The function isn't implemented.

    [EPERM]
        The cmd is IPC_RMID or IPC_SET and the calling process doesn't the
        appropriate privileges (that is, the ones set by shm_perm.cuid or
        shm_perm.uid in the data structure associated with shmid).

    The function may fail because of:

    [EOVERFLOW]
        The cmd is PC_STAT and the value of gid or uid is too large to be
        stored in the structure indicated by buf.

  SEE ALSO

    shmat(2)

    shmdt(2)

    shmget(2)

  USAGE NOTES

    The shmctl function is thread safe.

    The shmctl function is not async-signal safe.