0                  Successful completion.
    -1                 Indicates an error. The function sets errno to
                       one of the following values:

                       o  EINVAL - The value of the euid argument is
                          invalid and not supported.

                       o  EPERM - The process does not have the
                          IMPERSONATE privilege, and euid does not
                          match the real user ID or the saved set-
                          user-ID.