msgctl(2)                                                         msgctl(2)


   NAME
         msgctl - message control operations

   SYNOPSIS
         #include <sys/types.h>
         #include <sys/ipc.h>
         #include <sys/msg.h>

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

   DESCRIPTION
         msgctl 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 /* only access permission 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.cuid or 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.cuid or msg_perm.uid in the data structure
                     associated with msqid.

         msgctl fails if one or more of the following are true:

         EACCES         cmd is IPC_STAT and operation permission is denied to
                        the calling process [see intro(2)].

         EFAULT         buf points to an illegal address.

         EINVAL         msqid is not a valid message queue identifier.




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   msgctl(2)                                                         msgctl(2)


         EINVAL         cmd is not a valid command.

         EINVAL         cmd is IPC_SET and msg_perm.uid or msg_perm.gid is not
                        valid.

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

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

         EPERM          cmd is 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 that of super user.

   SEE ALSO
         intro(2), msgget(2), msgop(2).

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






























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