我使用Ubuntu 20.04，Nodemon 2.0.4，Node 14.9.0和Express 4.17.1。每次我保存代码时，都会得到这个错误：

events.js:291
      throw er; // Unhandled 'error' event
      ^

Error: listen EADDRINUSE: address already in use :::3000
    at Server.setupListenHandle [as _listen2] (net.js:1318:16)
    at listenInCluster (net.js:1366:12)
    at Server.listen (net.js:1452:7)
    at Function.listen (/home/ubuntu/kopum/node_modules/express/lib/application.js:618:24)
    at Object.<anonymous> (/home/ubuntu/kopum/app.js:37:5)
    at Module._compile (internal/modules/cjs/loader.js:1075:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1096:10)
    at Module.load (internal/modules/cjs/loader.js:940:32)
    at Function.Module._load (internal/modules/cjs/loader.js:781:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47
Emitted 'error' event on Server instance at:
    at emitErrorNT (net.js:1345:8)
    at processTicksAndRejections (internal/process/task_queues.js:80:21) {
  code: 'EADDRINUSE',
  errno: -98,
  syscall: 'listen',
  address: '::',
  port: 3000
}
[nodemon] app crashed - waiting for file changes before starting...

然后我试着在终端上运行这个：

sudo lsof -i :3000
kill -9 {PID}

然后我通过运行nodemon app.js重新启动Nodemon，一切都恢复正常。但是当我添加一些代码并保存它时，EADDRINUSE又回来了。