msgctl(2)                 SYSTEM CALLS                  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



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msgctl(2)                 SYSTEM CALLS                  msgctl(2)



                    identifier.

     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. Other-
     wise, a value of -1 is returned and errno is set to indicate
     the error.


























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