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msgctl(S)


msgctl -- message control operations

Syntax

cc ... -lc

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

int msgctl (msqid, cmd, buf) int msqid, cmd; struct msqid_ds *buf;

Description

The msgctl system call provides a variety of message control operations as specified by cmd. The following cmds are available:

IPC_RMID
Remove the message queue identifier specified by msqid from the system and destroy the message queue 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 msg_perm.cuid or msg_perm.uid in the data structure associated with msqid.

IPC_SET
Set the value of the following members of the data structure associated with msqid to the corresponding value found in the structure pointed to by buf:
   msg_perm.uid
   msg_perm.gid
   msg_perm.mode /* only low 9 bits */
   msg_qbytes

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 msg_perm.cuid or msg_perm.uid in the data structure associated with msqid. Only super user can raise the value of msg_qbytes.


IPC_STAT
Place the current value of each member of the data structure associated with msqid into the structure pointed to by buf. The contents of this structure are defined in Intro(S).

The msgctl system call fails if one or more of the following is true:


[EACCES]
The cmd argument is equal to IPC_STAT and {READ} operation permission is denied to the calling process.

[EFAULT]
The buf argument points to an illegal address.

[EINVAL]
1. The msqid argument is not a valid message queue identifier.
2. The cmd argument is not a valid command.

[EPERM]
1. The cmd argument is equal to IPC_RMID or IPC_SET. The effective user ID of the calling process is not equal to that of super user, or to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid.
2. The cmd argument is equal to IPC_SET, an attempt is being made to increase to the value of msg_qbytes, and the effective user ID of the calling process is not equal to that of super user.

Diagnostics

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

See also

Intro(S), msgget(S), msgop(S)

Standards conformance

msgctl is conformant with:

X/Open Portability Guide, Issue 3, 1989 .


© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003