为什么一些服务在系统启动后有时无法正常运行？

Issue

• 有些服务在引导时无法正确启动。但是，它们可以在以后正常启动。

• systemd 检测到的 ordering cycle，如下所示：

  # journalctl -b | egrep "Found|ordering cycle"
  ...
  systemd[1]: Found ordering cycle on sysinit.target/start
  systemd[1]: Found dependency on local-fs.target/start
  systemd[1]: Found dependency on data.mount/start
  systemd[1]: Found dependency on home.mount/start
  systemd[1]: Found dependency on network.target/start
  systemd[1]: Found dependency on NetworkManager-wait-online.service/start
  systemd[1]: Found dependency on basic.target/start
  systemd[1]: Found dependency on sysinit.target/start
  systemd[1]: Breaking ordering cycle by deleting job local-fs.target/start
  ...
  

• 文件 /run/nologin 存在且没有被自动删除，从而导致用户无法登录