So probably about a decade ago at this point I was working for free for a friend's start-up hosting company. He had rented out a high-end server in some data center and sold out virtualized chunks to clients.

This is back when you had only a few options for running virtual servers, but the market was taking off like a bat out of hell. In our case, we used User-Mode Linux (UML).

UML is essentially a kernel hack that lets you run the kernel in user space. That alone helps keep things separate or jailed. I'm pretty sure some of you can shed more light on it, but that's as I understood it at the time and I wasn't too shabby at hacking the kernel when we'd have driver issues.

Anyway, one of the ways my friend would on-board someone was to generate a new disk image file, mount it, and then chroot to that mount path. He'd basically use a stock image to do this and then wipe it out before putting it live.

I'm not sure exactly what he was doing at the time, but I got a panicked message on New Years Day saying that he had deleted everything. By everything, he had done an rm -fr /home as root on what he had thought was the root of a drive image.

It wasn't an image. It was the host server.

In the stoke of a single command, all user data was lost. We were pretty much screwed, but I have a knack for not giving up - so I spent a ton of time investigating linux file recovery.

Fun fact about UML - since the kernel runs in user space as a regular ol' process, anything it opens is attached to that process. I had noticed that while the files were "gone", I could still see disk usage. I ended up finding the images attached to their file pointers associated with each running kernel - and thankfully all customers were running at the time.

The next part was crazy, and I still think is crazy. I don't remember the command, but I had to essentially copy the image from the referenced path into a new image file, then shutdown the kernel and power it back on from the new image. We had configs all set aside, so that was easy. When it finally worked I was floored.

Rinse and repeat, I managed to drag every last missing bit out of /proc - with the only side effect being that all MySQL databases needed to be cleaned up.