shmctl.2 (2010 09)

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shmctl(2) shmctl(2)

NAME

shmctl() - shared memory control operations

SYNOPSIS

#include <sys/shm.h>

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

DESCRIPTION

The shmctl() system call provides a variety of shared memory control operations as speciﬁed by the

cmd argument. cmd can have the following values:

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).

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 a user having appropriate privileges or to the value of either

shm_perm.uid or shm_perm.cuid in the data structure associated with shmid.

This cmd cannot be executed on a shared memory segment that has been created

with relaxed isolation .

IPC_RMID Remove the shared memory identiﬁer speciﬁed by shmid from the system and des-

troy the shared memory segment and data structure associated with it. If the seg-

ment is attached to one or more processes, then the segment key is changed to

IPC_PRIVATE and the segment is marked removed. The segment disappears

when the last attached process detaches it. This cmd can only be executed by a pro-

cess that has an effective user ID equal to either that of a user with appropriate

privileges or to the value of either shm_perm.uid or shm_perm.cuid

in the

data structure associated with shmid.

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 that of a user

having appropriate privileges or has an effective user ID equal to the value of either

shm_perm.uid or shm_perm.cuid in the data structure associated with shmid

and has the

PRIV_MLOCK privilege (see getprivgrp (2)).

SHM_UNLOCK Unlock the shared memory segment speciﬁed by shmid. This cmd can only be exe-

cuted by a process that either has an effective user ID equal to a user having

appropriate privileges or has an effective user ID equal to the value of either

shm_perm.uid or shm_perm.cuid in the data structure associated with shmid

and has the PRIV_MLOCK privilege (see getprivgrp (2)).

RETURN VALUE

shmctl() returns the following values:

0 Successful completion.

-1 Failure. errno is set to indicate the error.

ERRORS

shmctl() fails, errno is set to one of the following values.

[EACCES] cmd is equal to

IPC_STAT and Read operation permission is denied to the calling

process (see shared memory operation permissions in glossary (9)).

[EFAULT] buf points to an illegal address. The reliable detection of this error is implementa-

tion dependent.

[EINVAL] cmd is equal to

SHM_UNLOCK and the shared-memory segment speciﬁed by shmid

is not locked in memory.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (2 pages)

PAGE 1
shmctl(2) shmctl(2) NAME shmctl() - shared memory control operations SYNOPSIS #include int shmctl(int shmid, int cmd, struct shmid_ds *buf); DESCRIPTION The shmctl() system call provides a variety of shared memory control operations as specified by the cmd argument. cmd can have the following values: 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).
PAGE 2
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. Recompile the application with the latest /usr/include/sys/ipc.