code: def _find_cgroup_mounts():
      
      try:
          with open('/proc/mounts', 'rt') as mountsFile:
              for mount in mountsFile:
                  mount = mount.split(' ')
                  if mount[2] == 'cgroup':
                      mountpoint = mount[1]
                      options = mount[3]
                      for option in options.split(','):
                          if option in ALL_KNOWN_SUBSYSTEMS:
                              yield (option, mountpoint)
      except IOError:
          logging.exception('Cannot read /proc/mounts')
docs: Return the information which subsystems are mounted where.
      @return a generator of tuples (subsystem, mountpoint)