title: Systemd: service doesn't restart with WatchdogSec option set
body: <p>I'm trying to manager my vm with systemd. In case the qemu crashes, I want to implement watchdog for the service, following is the unit file.  </p>
  
  <pre><code>[Unit]
  Description=vm manager
  After=network.target
  Before=shutdown.target reboot.target poweroff.target halt.target
  
  [Service]
  Type=forking
  ExecStart=/root/vm/vm-manager.sh start-vm
  ExecStop=/root/vm/vm-manager.sh stop-vm
  KillSignal=SIGCONT
  PIDFile=/root/vm/run/pid
  WatchdogSec=30s
  Restart=on-failure
  
  [Install]
  WantedBy=multi-user.target
  </code></pre>
  
  <p>I didn't call sd_notify(0, "WATCHDOG=1") in my application, above is the background. I have two questions:</p>
  
  <ol>
  <li>In my opinion, this service should be restarted after 30s, why it keeps running until I kill or stop it?</li>
  <li>When I kill qemu manually(I take qemu process as the main process), the service restart immediately, without waiting.</li>
  </ol>
  
  <p>Besides the two questions, if there's anything wrong or suggestion about the unit file, please raise it freely.</p>
  
  <p>Thanks!</p>