How do I know if I'm in a jail, container, snapshot, etc. environment? [duplicate]

This question is an exact duplicate of:

• Ubuntu user disappeared from machine 1 answer

I received a machine (Ubuntu 12.04 server) from a coworker when he left the company. I created my own user as sudo/admin and used the machine for months via SSH. After rebooting for the first time since I was given the machine, I discovered that my user and everything I installed were missing. My user wasn't in the /etc/passwd file and the /home/myuser directory was missing. When I recreated the user and reinstalled everything, I didn't get any suspicious errors.

I suspect that I might have been in a snapshot/jail/container environment the whole time before rebooting, but how can I tell?