Problem: A port is being used by some process but the pid of process is not visible
When the process is started by
root, other users not in the root group cannot view the process ids. So when you do:
process id will not be visible to normal user.
You have to run
netstat command with
sudo, to view all process ids.
sudo netstat -atnp
A scenario I came across is when Apache tomcat was started as a Java service with jsvc command. The daemon.sh was run by the root user, so the process belonged to root.