osf1 man page for msgctl

msgctl(2)							System Calls Manual							 msgctl(2)

NAME
       msgctl - Performs message control operations

SYNOPSIS
       #include <sys/msg.h>

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

       Application developers may want to specify #include statements for <sys/types.h> and <sys/ipc.h> before the one for <sys/msg.h> if programs
       are being developed for multiple platforms. The additional #include statements are not required on Tru64 UNIX systems or by ISO	or  X/Open
       standards, but may be required on other vendors' systems that conform to these standards.

STANDARDS
       Interfaces documented on this reference page conform to industry standards as follows:

       msgctl():  XSH5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS
       Specifies  the  message	queue  ID.   Specifies the type of command.  The possible commands and the operations they perform are as follows:
       Queries the message queue ID by copying the contents of its associated data structure into the buf structure.  The process must have manda-
       tory  read  access  to the message queue with respect to all access control policies.  Sets the message queue ID by copying values found in
       the buf structure into corresponding fields in the msqid_ds structure associated with the message queue ID.  This operation is  restricted.
       The  effective  user ID of the calling process must be equal to that of superuser or equal to the value of msg_perm.uid or msg_perm.cuid in
       the associated msqid_ds structure.  Only superuser can raise the value of msg_qbytes.  Removes the message queue  ID  and  deallocates  its
       associated  msqid_ds structure.	This operation is restricted.  The effective user ID of the calling process must be equal to that of supe-
       ruser or equal to the value of msg_perm.uid or msg_perm.cuid in the associated msqid_ds structure.  Points to a msqid_ds  structure.   This
       structure is used only with the IPC_STAT and IPC_SET commands.  With IPC_STAT, the results of the query are copied to this structure.  With
       IPC_SET, the values in this structure are used to set the corresponding fields in the msqid_ds structure associated with the message  queue
       ID.  In either case, the calling process must have allocated the structure before making the call.

DESCRIPTION
       The  msgctl()  function allows a process to query or set the contents of the msqid_ds structure associated with the specified message queue
       ID.  It also allows a process to remove the message queue ID and its associated msqid_ds structure.  The cmd value determines which  opera-
       tion is performed.

       The  IPC_SET command uses the user-supplied contents of the buf structure to set the following members of the msqid_ds structure associated
       with the message queue ID: The owner's user ID.	The owner's group ID.  The access modes for the queue.	Only the low-order nine  bits  are
       set.  The maximum number of bytes on the queue.	The time of the last msgctl() operation that changed the structure.

RETURN VALUES
       Upon  successful  completion,  msgctl(  returns a value of 0 (zero).  Otherwise, a value of -1 is returned and errno is set to indicate the
       error.

ERRORS
       The msgctl() function sets errno to the specified values for the following conditions: The cmd  parameter  is  IPC_STAT,  but  the  calling
       process	does not have read permission.	[Tru64 UNIX]  The cmd parameter is IPC_STAT or IPC_SET, and an error occurred in accessing the buf
       structure.  The msqid parameter is not a valid message queue ID, or the cmd parameter is not a valid command.  The cmd parameter  is  equal
       to  either IPC_RMID or IPC_SET, and the calling process does not have appropriate privilege.  The cmd parameter is equal to IPC_SET, and an
       attempt is being made to increase the value of the msg_qbytes parameter when the calling process does not have the superuser privilege.

RELATED INFORMATION
       Functions: msgget(2), msgrcv(2), msgsnd(2)

       Data Structures: msqid_ds(4)

       Standards: standards(5) delim off

																	 msgctl(2)