Sometimes when trying to start an app you find that the port is in use. You can figure out what that program is by running:
$ lsof -i :8000
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
squid3 1289 proxy 15u IPv6 14810490 0t0 TCP *:8000 (LISTEN)
To see more information based on the pid
:
$ ps -fp 1289
UID PID PPID C STIME TTY TIME CMD
proxy 1289 1 0 09:48 ? 00:00:00 /usr/sbin/squid3 -N -f /etc/squid-deb-proxy/squid-deb-proxy.conf
Then you can kill the program with
$ kill -SIGKILL 1289