unix:///tmp/supervisor.sock no such file

I had the same problem. After reading the man supervisorctl manual I realized the default file is /etc/supervisord.conf which in ubuntu is at /etc/supervisor/supervisord.conf. I created a symlink using:

sudo ln -s  /etc/supervisor/supervisord.conf /etc/supervisord.conf

This fixed my problem.

Running this command sudo service supervisord restart solved my issue.

Some answers suggest re-installation, which is essentially doing this

Finally solved it by reinstalling supervisor after deleting all configuration files in /etc/supervisor/conf.d/ this did the trick.