For a while, I've been getting "ERROR: Another cron is running" when trying to run
barman cron. In the process of looking for the stray lock file, I realized that the problem was actually a permissions one. I was running barman with a regular user account, not the
/var/lib/barman was chowned by
barman:barman. Once I set this, barman cron runs fine.
It would be great, in the case that the lock file check fails, to check directory permissions and give a more sensible error message.