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;

HP-UX COMPATIBILITY

Level: HP-UX/STANDARD

Origin: System V

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 glossary(9). {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 either that of super-user or to the value of either shm_perm.uid or shm_perm.cuid 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 either shm_perm.uid or shm_perm.cuid in the data structure associated with shmid.

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 glossary(9)).

[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, nor is it equal to the value of shm_perm.uid or shm_perm.cuid in the data structure associated with shmid.

[EFAULT] Buf points to an illegal address.

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.

HARDWARE DEPENDENCIES

Series 200 and 500:

Two additional shared memory control operations as specified by cmd are available:

SHM_LOCK Lock the shared memory segment specified by shmid in memory. This cmd can only be executed by a process that either has an effective user ID equal to super-user or has PRIV_MLOCK privilege (see setprivgrp(2)).

SHM_UNLOCK Unlock the shared memory segment specified by shmid. This cmd can only be executed by a process that either has an effective user ID equal to super-user or has PRIV_MLOCK privilege (see setprivgrp(2)).

Shmctl will fail if one or more of the following are true:

[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 and the calling process does not have PRIV_MLOCK privilege (see setprivgrp(2)).

[EINVAL] Cmd is equal to SHM_UNLOCK and the shared-memory segment specified by shmid is not locked in memory.

Museum