I have Ubuntu running on an old desktop as a local file server, and it's been working fine for the last three months without me ever needing to touch it, however today I wanted to change some configuration, and found that I could not SSH to it (connection refused). I plugged a keyboard and monitor into the box, and I could not even 'ssh localhost' successfully (connection refused). 'ps -aux | grep ssh' shows only ssh-agent is running, and when I tried to restart the service, it said that sshd (and just ssh, I tried that too) wasn't a recognized service. 'dpkg -l | grep ssh' lists openssh-client, but not openssh-server.
Now, I assume I could probably install openssh-server and everything would be fine again, but I'm quite confused as to what possibly could have caused this. dpkg.log makes no mention of openssh-server ever being installed, let alone uninstalled, which doesn't make sense considering I'd ssh'd to the machine in the past just fine. Is there some other package Ubuntu comes with that would let me SSH to it?