When a node application crashes unexpectedly, you might get a EADDRINUSE, Address already in use error when you try to restart it. This means that the port you’re using is already being used by the crashed application. What you need to do is fun the PID of that process, and then kill it. There’s more than one way to skin that cat, but I like to use netstat. N.B. You’ll need to run this as sudo for it to work.

sudo netstat -tulpn

This will produce something like the following. You want to look in the Local Address column for the port your app was using. Suppose you’re using port 3000, which appears on the next to last line. The PID for that process (and the name of the program using that process as a sanity check) can be found on the last column.

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name
tcp        0      0 127.0.0.1:199               0.0.0.0:*                   LISTEN      3374/snmpd
tcp        0      0 0.0.0.0:775                 0.0.0.0:*                   LISTEN      3137/rpc.statd
tcp        0      0 0.0.0.0:53644               0.0.0.0:*                   LISTEN      -
tcp        0      0 0.0.0.0:111                 0.0.0.0:*                   LISTEN      3094/portmap
tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN      3679/sshd
tcp        0      0 0.0.0.0:3000                0.0.0.0:*                   LISTEN      25011/node
tcp        0      0 :::22                       :::*                        LISTEN      3679/sshd

Then, to kill that process you would say,

kill -9 25011

I’ve seen other people use these solutions on Stack Overflow. Notably, running

ps aux | grep "node"

Which returns,

root     25011  0.2  0.0 1966296    8 pts/16   Sl+  Jul20   8:21 node app.js

In this case, the PID is found in the second column.