Yet another command that I don't use often and always need to search for it. The reason that I write about this here is to find is easily next time…
$ sudo service nginx start
Response I got was
bind() to 0.0.0.0:80 failed (98: Address already in use). Trying
restart does not help and it's not the first time. Then this command comes to rescue:
$ sudo fuser -k 80/tcp
This will kill old nginx instance for sure. Or anything else that listens to port 80.