docs: def _double_fork(self):
          """Do the UNIX double-fork magic.
  
          See Stevens' "Advanced Programming in the UNIX Environment" for details
          (ISBN 0201563177)
          http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
          """
          try:
  
              pid = os.fork()
              if pid > 0:
  
                  # Exit first parent.
                  sys.exit(0)
                  return None
  
          except OSError as err:
  
              LOG.exception(
                  "Fork #1 failed: {0} ({1})".format(
                      err.errno,
                      err.strerror,
                  ),
              )
              sys.exit(exit.DAEMONIZE_FAILED)
              return None
  
          # Decouple from parent environment.
          os.chdir("/")
          os.setsid()
          os.umask(0)
  
          # Do second fork.
          try:
  
              pid = os.fork()
              if pid > 0:
  
                  # Exit from second parent.
                  sys.exit(0)
  
          except OSError as err:
  
              LOG.exception(
                  "Fork #2 failed: {0} ({1})".format(
                      err.errno,
                      err.strerror,
                  ),
              )
              sys.exit(exit.DAEMONIZE_FAILED)
              return None