Supervisor on Debian Wheezy: another program is already listening on a port that one of our HTTP servers is configured to use

I solved my problem by unlinking the .sock file.

sudo unlink /var/run/supervisor.sock

If this does not help you should check and unlink the file at /tmp/supervisor.sock.

Type this in your terminal

ps -ef | grep supervisord

You will get some pid of supervisord just like these

root   2503  1  0 Nov19 ?  00:03:23 /usr/bin/python /usr/bin/supervisord
root   21337 2556  0 18:15 pts/8   00:00:00 grep --color=auto supervisord

And the PID is 2503

Then type this:

kill -s SIGTERM 2503  

It should work

Similar to @N'falyKaba's answer but perhaps a bit more direct, as of newer versions of Supervisor you can use supervisorctl pid to get the pid, kill it, and restart:

$ kill -s SIGTERM $(supervisorctl pid)

To restart:

$ supervisord -c /path/to/supervisord.conf

Source: docs.