Description

   The kill function is restricted to C and C++ programs that
   include the main function.

   The kill function sends a signal to a process, as if the process
   had called raise. If the signal is not trapped or ignored by the
   target program, the program exits.

   OpenVMS VAX and Alpha implement different rules about what
   process you are allowed to send signals to. A program always has
   privileges to send a signal to a child started with vfork/exec.
   For other processes, the results are determined by the OpenVMS
   security model for your system.

   Because of an OpenVMS restriction, the kill function cannot
   deliver a signal to a target process that runs an image installed
   with privileges.

   Unless you have system privileges, the sending and receiving
   processes must have the same user identification code (UIC).

   On OpenVMS systems before Version 7.0, kill treats a signal value
   of 0 as if SIGKILL were specified.

   For OpenVMS Version 7.0 and higher systems, if you include
   <stdlib.h> and compile with the _POSIX_EXIT feature-test macro
   set, then:

   o  If the signal value is 0, kill validates the process ID but
      does not send any signals.

   o  If the process ID is not valid, kill returns -1 and sets errno
      to ESRCH.