MSGCTL(S)                XENIX System V                 MSGCTL(S)



     Name
          msgctl - Provides message control operations.

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

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

     Description
          msgctl provides for message control operations specified by
          cmd.

          The cmds available are:

          IPC_STAT
                 Places the current value of each member of the data
                 structure associated with msqid into the structure
                 pointed to by buf.  Contents of this structure are
                 defined in intro(S).

          IPC_SETSets the value of the following members of the data
                 structure associated with msqid into the structure
                 pointed to by buf:
                        msg_perm.uid
                        msg_perm.gid
                        msg_perm.mod /* only low 9 bits*/
                        msg_qbytes

                This cmd can only be executed by a process that has an
                effective user ID equal to either a super-user or to
                the value of msg_perm.uid in the data structure
                associated with msqid.  Only a super-user can raise
                the value of msg_qbytes.

          IPC_RMID
                 Removes the message queue identifier specified by
                 msqid from the system and destroys 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 a super-user or to the value
                 of msg_perm.uid in the data structure associated with
                 msqid.

          msgctl will fail if one or more of the following are true:

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




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     MSGCTL(S)                XENIX System V                 MSGCTL(S)



               cmd is not a valid command.  [EINVAL]

               cmd is equal to IPC_STAT and buf points to an address
               in read-only shared data.  [EINVAL]

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

               cmd is equal to IPC_RMID or IPC_SET.  The effective
               user ID of the calling process does not equal that of a
               super-user nor does it equal the value of msg_perm.uid
               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.

               buf points to an illegal address.  [EFAULT]

     Return Value
          A value of 0 is returned upon successful completion.
          Otherwise, -1 is returned and errno is set to indicate the
          error.

     See Also
          intro(S), msgget(S), msgop(S)

     Notes
          Programs using this function must be compiled with the -Me
          compiler option.























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