Description

   The setgid function can be used with POSIX style identifiers
   enabled or disabled.

   POSIX style IDs are supported on OpenVMS Version 7.3-2 and
   higher.

   With POSIX IDs disabled, the setgid function is implemented for
   program portability and serves no function. It returns 0 (to
   indicate success).

   With POSIX style IDs enabled:

   o  If the process has the IMPERSONATE privilege, the setgid
      function sets the real group ID, effective group ID, and the
      saved set-group-ID to gid.

   o  If the process does not have appropriate privileges but gid is
      equal to the real group ID or to the saved set-group-ID, then
      the setgid function sets the effective group ID to gid. The
      real group ID and saved set-group-ID remain unchanged.

   o  Any supplementary group IDs of the calling process remain
      unchanged.