msgctl(2) [sunos man page]

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 privi-
		       leges  asserted	in the effective set or equal to the value of msg_perm.cuid or	msg_perm.uid in the data structure associ-
		       ated 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)

SunOS 5.10							    22 Mar 2004 							 msgctl(2)

MSGCTL(2)						      BSD System Calls Manual							 MSGCTL(2)

NAME

     msgctl -- message control operations

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/msg.h>

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

DESCRIPTION

     The msgctl() system call performs control operations on the message queue specified by msqid.

     Each message queue has a msqid_ds structure associated with it which contains the following members:

	 struct ipc_perm msg_perm; /* msg queue permission bits */
	 msgqnum_t msg_qnum;	   /* # of msgs in the queue */
	 msglen_t  msg_qbytes;	   /* max # of bytes on the queue */
	 pid_t	   msg_lspid;	   /* pid of last msgsnd() */
	 pid_t	   msg_lrpid;	   /* pid of last msgrcv() */
	 time_t    msg_stime;	   /* time of last msgsnd() */
	 time_t    msg_rtime;	   /* time of last msgrcv() */
	 time_t    msg_ctime;	   /* time of last msgctl() */

     The ipc_perm structure used inside the msgid_ds structure is defined in <sys/ipc.h> and contains the following members:

	 uid_t cuid;  /* creator user id */
	 gid_t cgid;  /* creator group id */
	 uid_t uid;   /* user id */
	 gid_t gid;   /* group id */
	 mode_t mode; /* permission (lower 9 bits) */

     The operation to be performed by msgctl() is specified in cmd and is one of:

     IPC_STAT	Gather information about the message queue and place it in the structure pointed to by buf.

     IPC_SET	Set the value of the msg_perm.uid, msg_perm.gid, msg_perm.mode and msg_qbytes fields in the structure associated with msqid.  The
		values are taken from the corresponding fields in the structure pointed to by buf.  This operation can only be executed by the
		super-user, or a process that has an effective user id equal to either msg_perm.cuid or msg_perm.uid in the data structure associ-
		ated with the message queue.  The value of msg_qbytes can only be increased by the super-user.	Values for msg_qbytes that exceed
		the system limit (MSGMNB from <sys/msg.h>) are silently truncated to that limit.

     IPC_RMID	Remove the message queue specified by msqid and destroy the data associated with it.  Only the super-user or a process with an
		effective uid equal to the msg_perm.cuid or msg_perm.uid values in the data structure associated with the queue can do this.

     The permission to read from or write to a message queue (see msgsnd(2) and msgrcv(2)) is determined by the msg_perm.mode field in the same
     way as is done with files (see chmod(2)), but the effective uid can match either the msg_perm.cuid field or the msg_perm.uid field, and the
     effective gid can match either msg_perm.cgid or msg_perm.gid.

RETURN VALUES

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

ERRORS

     msgctl() will fail if:

     [EPERM]		cmd is equal to IPC_SET or IPC_RMID and the caller is not the super-user, nor does the effective uid match either the
			msg_perm.uid or msg_perm.cuid fields of the data structure associated with the message queue.

			An attempt was made to increase the value of msg_qbytes through IPC_SET, but the caller is not the super-user.

     [EACCES]		cmd is IPC_STAT and the caller has no read permission for this message queue.

     [EINVAL]		msqid is not a valid message queue identifier.

			cmd is not a valid command.

     [EFAULT]		buf specifies an invalid address.

SEE ALSO

     msgget(2), msgrcv(2), msgsnd(2)

STANDARDS

     The msgctl system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5'').

HISTORY

     Message queues appeared in the first release of AT&T System V UNIX.

BSD
								  August 25, 1999							       BSD