msgctl(2)                                                         msgctl(2)




 NAME    [Toc]    [Back]
      msgctl - message control operations

 SYNOPSIS    [Toc]    [Back]
      #include <sys/msg.h>

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

 DESCRIPTION    [Toc]    [Back]
      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 glossary(9).

           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 low 9 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 either msg_perm.uid
                          or msg_perm.cuid in the data structure associated
                          with msqid.  Only super-user can raise the value
                          of msg_qbytes.

                          WARNING: Programs compiled on HP-UX revisions
                          prior to 11.11 use old 16-bit msqid_ds structure
                          fields (obtained via IPC_STAT) which can describe
                          queue sizes only up to 64KBytes. Care must be
                          taken such that queues shared with such programs
                          are not made larger than 64KBytes (65535).  Or,
                          those existing programs should be recompiled.  Or,
                          the system administrator should restrict the
                          MSGMNB kernel tunable parameter to 64KBytes or
                          less.

           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 superuser
 or to the value of either msg_perm.uid or



 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003






 msgctl(2)                                                         msgctl(2)




                          msg_perm.cuid in the data structure associated
                          with msqid.

 RETURN VALUE    [Toc]    [Back]
      Upon successful completion, a value of 0 is returned.  Otherwise, a
      value of -1 is returned and errno is set to indicate the error.

 ERRORS    [Toc]    [Back]
      msgctl() fails if one or more of the following is true:

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

      [EINVAL]       cmd is not a valid command, or the command contains
                     invalid parameters.

      [EACCES]       cmd is equal to IPC_STAT and Read operation permission
                     is denied to the calling process (see message operation
                     permissions in glossary(9)).

      [EPERM]        cmd is equal to IPC_RMID or IPC_SET and the effective
                     user ID of the calling process is not equal to that of
                     a user who has appropriate privileges and it is not
                     equal to the value of either msg_perm.uid or
                     msg_perm.cuid in the data structure associated with
                     msqid.

      [EPERM]        cmd is equal to 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 equal to that of
                     super-user.

      [EFAULT]       buf points to an illegal address.  Reliable detection
                     of this error is implementation dependent.

 SEE ALSO    [Toc]    [Back]
      ftok(3C), ipcrm(1), ipcs(1), msgget(2), msgop(2).

 STANDARDS CONFORMANCE    [Toc]    [Back]
      msgctl(): SVID2, SVID3, XPG2, XPG3, XPG4


 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003