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(5) for descriptions of the following attributes:


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

SEE ALSO


Intro(2), msgget(2), msgrcv(2), msgsnd(2), attributes(5), privileges(5),
standards(5)


March 22, 2004 MSGCTL(2)