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System Interface Guide

Controlling Message Queues

The msgctl(2) function alters the permissions and other characteristics of a message queue. The msqid argument must be the ID of an existing message queue. The cmd argument is one of the following:

IPC_STAT

Place information about the status of the queue in the data structure pointed to by buf. The process must have read permission for this call to succeed.

IPC_SET

Set the owner's user and group ID, the permissions, and the size (in number of bytes) of the message queue. A process must have the effective user ID of the owner, creator, or superuser for this call to succeed.

IPC_RMID

Remove the message queue specified by the msqid argument.

The following code illustrates msgctl(2) with all its various flags:

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

 	...
 	if (msgctl(msqid, IPC_STAT, &buf) == -1)  {
 		perror("msgctl: msgctl failed");
 		exit(1);
 	}
 	...
 	if (msgctl(msqid, IPC_SET, &buf) == -1) {
 		perror("msgctl: msgctl failed");
 		exit(1);
 	}
 	...