Rosbridge TCP server is no longer starting

edit

For the past year or so I have been using the following command to start up a rosbridge on my computer:

roslaunch rosbridge_server rosbridge_tcp.launch bson_only_mode:=True

Up until recently I would see the confirmation "Rosbridge TCP Server started on port 9090" and it worked as expected. Now when I run that same command I get the message "trying to start rosbridge TCP server.." printed repeatedly every second or two until I ctrl+c out.

Does anyone know what I can do to get my rosbridge working again? I'm using ROS melodic and ros-melodic-rosbridge-server on Ubuntu 18.04 4.15.0-128-generic.

edit: I solved the problem that I was seeing. The issue was that there was another process that was still using port 9090 on my machine. In fact, I suspect it was the remnants of a previous rosbridge process that I had going when my computer crashed for an unrelated reason a while back. To fix the issue, I used the lsof command to find which process was using that port and then killed it.

$ sudo lsof -i TCP:9090 | grep LISTEN
  python2 23156 corwinjs   13u  IPv4 37621397      0t0  TCP *:9090 (LISTEN)
$ kill -9 23156

Rosbridge was able to start successfully after that!