MSGCTL(2) System Calls MSGCTL(2)

NAME

msgctl - message control operations

SYNOPSIS

#include <sys/msg.h>

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

DESCRIPTION

The msgctl() function provides a variety of message control
operations as specified by cmd. The following cmds 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 Intro(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 /* access permission bits only */
msg_qbytes

This command can be executed only by a process that has
either the {PRIV_IPC_OWNER} privilege or an effective
user ID equal to the value of msg_perm.cuid or
msg_perm.uid in the data structure associated with msqid.
Only a process with the {PRIV_SYS_IPC_CONFIG} privilege
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
either with appropriate privileges asserted in the
effective set or equal to the value of msg_perm.cuid or
msg_perm.uid in the data structure associated with msqid.
The buf argument is ignored.

RETURN VALUES

Upon successful completion, msgctl() returns 0. Otherwise, it returns
-1 and sets errno to indicate the error.

ERRORS

The msgctl() function will fail if:

EACCES
The cmd argument is IPC_STAT and operation permission is
denied to the calling process (see Intro(2)).


EFAULT
The buf argument points to an illegal address.


EINVAL
The msqid argument is not a valid message queue
identifier; or the cmd argument is not a valid command
or is IPC_SET and msg_perm.uid or msg_perm.gid is not
valid.


EOVERFLOW
The cmd argument is IPC_STAT and uid or gid is too large
to be stored in the structure pointed to by buf.


EPERM
The cmd argument is IPC_RMID or IPC_SET, the
{PRIV_SYS_IPC_OWNER} privilege is not asserted in the
effective set of the calling process, and is not equal
to the value of msg_perm.cuid or msg_perm.uid in the
data structure associated with msqid.

The cmd argument is IPC_SET, an attempt is being made to
increase to the value of msg_qbytes, and the
{PRIV_SYS_IPC_CONFIG} privilege is not asserted in the
effective set of the calling process.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+

SEE ALSO

Intro(2), msgget(2), msgrcv(2), msgsnd(2), attributes(7),
privileges(7), standards(7)

March 22, 2004 MSGCTL(2)