Selenium: Invalid “already running” error when starting server

Question

I am trying to get the Selenium server up and running. However, when I type:

java -jar selenium-server-standalone-2.0b3.jar

I get an Exception

Answer 1

If you get a 403 error on 127.0.01:4444 and not a 404 one, something is running there. (You're positive it cannot be a previous instance Selenium ? It'd be the most logical.)

Sometimes Selenium continue running in the background after an unexpected exit. I'd suggest checking the running processes, or rebooting the machine if everything else fails.

It happens to me frequently when Hudson asks Selenium-Server to run some tests and it fails in the middle for some reasons. Killing the process solves the problem.