Controlling Message Queues

msgctl() 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() with all its 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);
        }
...