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 kedef(2). Read permission is required.

    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 super-user or to the value of 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 either that of super-user or to the value of shm_perm.uid in the data structure associated with shmid.

RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

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 kedef(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 and it is not equal to the value of shm_perm.uid in the data structure associated with shmid.

EFAULT
    Buf points to an illegal address.

SEE ALSO
kedef(2), shmget(2), shmop(2).