docs: def _init_sys_auto_lookup(self):
          """Return a list of tuples of available init systems on the
          current machine.
  
          Note that in some situations (Ubuntu 14.04 for instance) more than
          one init system can be found.
          """
          # TODO: Instead, check for executables for systemd and upstart
          # systemctl for systemd and initctl for upstart.
          # An alternative might be to check the second answer here:
          # http://unix.stackexchange.com/questions/196166/how-to-find-out-if-a-system-uses-sysv-upstart-or-systemd-initsystem
          # TODO: Move to each system's implementation
          init_systems = []
          if self._is_init_system_installed('/usr/lib/systemd'):
              init_systems.append('systemd')
          if self._is_init_system_installed('/usr/share/upstart'):
              init_systems.append('upstart')
          if self._is_init_system_installed('/etc/init.d'):
              init_systems.append('sysv')
          return init_systems