shmctl.2 (2010 09)

shmctl(2) shmctl(2)

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

[EINVAL] cmd is not a valid command, or the command contains invalid parameters.

[ENOMEM] cmd is equal to

SHM_LOCK and there is not sufﬁcient lockable memory to ﬁll the

request.

[EOVERFLOW]

cmd is equal to

IPC_STAT. The attached process count of a shared memory object

is too large for the ﬁeld in the data structure provided by the application. Recom-

pile the application with the latest /usr/include/sys/ipc.h

ﬁle to resolve

this issue.

[EPERM] cmd is equal to

IPC_RMID, IPC_SET

, SHM_LOCK,orSHM_UNLOCK and the

effective user ID of the calling process is not equal to that of a user having appropri-

ate privileges and it is not equal to the value of either

shm_perm.uid or

shm_perm.cuid in the data structure associated with shmid.

cmd is equal to

IPC_SET and the shared memory segment has

relaxed isola-

tion.

[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 a user having appropriate privileges and the calling

process does not have the

PRIV_MLOCK privilege (see getprivgrp (2)).

EXAMPLES

The following call to

shmctl() locks in memory the shared memory segment represented by myshmid.

This example assumes the process has a valid shmid, which can be obtained by calling shmget (2).

shmctl (myshmid, SHM_LOCK, 0);

The following call to shmctl() removes the shared memory segment represented by myshmid. This

example assumes the process has a valid shmid, which can be obtained by calling shmget() (see

shmget(2).

shmctl (myshmid, IPC_RMID, 0);

AUTHOR

shmctl() was developed by AT&T and HP.