MSGCTL(2)

NAME
msgctl - message control operations

SYNOPSIS
#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
msgctl provides a variety of message control operations as specified by cmd. The following commands are available:

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 kedef(2).

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

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.uid in the data structure associated with msqid.

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

ERRORS

msgctl will fail if:

EINVAL
    msqid is not a valid message queue identifier.

EINVAL
    cmd is not a valid command.

EACCES
    cmd is equal to IPC_STAT and read permission is denied to the calling process (see kedef(2)).

EPERM
    cmd is equal to IPC_RMID or IPC_SET. The effective user ID of the calling process is not equal to that of super user and it is not equal to the value of msg_perm.uid in the data structure associated with msqid.

EPERM
    cmd 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.

EFAULT
    Buf points to an illegal address.

SEE ALSO
kedef(2), msgget(2), msgop(2)