atd dead but subsys locked

After I killed the atd process by hand (sudo kill ), I can no longer start at jobs: [vagrant@localhost ~]$ echo ls | at 'now + 1 minute' job 6 at 2016-05-09 20:17 Can't open /var/run/atd.pid to signal atd. No atd running? Also, I see: [vagrant@localhost ~]$ service atd status atd dead but subsys locked [vagrant@localhost ~]$ service atd restart Stopping atd: [FAILED] Starting atd: [FAILED] [vagrant@localhost ~]$ I could reboot, since this is a Vagrant box expressly for playing around with, but I'd rather learn the "right way" to fix this. How do I get atd running again? (I'm running CentOS 6.6.)