code: def get_free_space(self):
          
          cmd = "df -k | grep -vE '^Filesystem|tmpfs|cdrom|none|udev|cgroup' | awk '{ print($1 \" \" $4 }'"
          lines = [_ for _ in self.run(cmd).strip().split('\n') if _.startswith('/')]
          assert len(lines) == 1, 'Ambiguous devices: %s' % str(lines)
          device, kb = lines[0].split(' ')
          free_space = int(kb) * 1024
          self.vprint('free_space (bytes):', free_space)
          return free_space
docs: Return free space in bytes.