Recently, there was a Mailman upgrade that seems to break Mailman if you don’t have a list called “mailman” on your server. Symptoms of this error include:

/var/log/mailman/error
mailmanctl(2801): PID unreadable in: /var/run/mailman/mailman.pid
mailmanctl(2801): [Errno 2] No such file or directory: '/var/run/mailman/mailman.pid'
mailmanctl(2801): Is qrunner even running?


If you try to restart mailman
/etc/rc2.d/S20mailman restart
and get the same error, then you need to check whether you have a “mailman” list on your server.

To install mailman list, follow this resource:
http://www.askdavetaylor.com/why_is_mailman_complaining_site_list_is_missing_mailman.html

After installing the mailman list, you can try restarting the mailman qrunner service to see if it works.
/etc/rc2.d/S20mailman start