A login session (under Jessie) running
certbot -d example.com -d www.example.com froze, and when I tried to run Let's Encrypt's certbot from another session, it said, "Another instance of Certbot is already running." I did a
kill -HUP on the still-running process, and tried to run certbot with a
--config-dir argument among other things, and got the same error.
How can I ask for the first attempt to be forgotten?
Is there a lockfile I can delete?