So I turned on my MBP (mid-2012, Sierra, 10GB RAM, 250GB SSD) today, and I was surprised to see that OSX wanted to install.

I only use this laptop for online classes and occasional browsing, so I wasn't worried about a reinstall. Got to the point of naming my home folder, and was not able to use my preferred choice. It was automatically being appended with a 1. This made me think that my original /home folder was still intact. I created a new user and finished the install.

Sure enough, I was able to log in normally to my original user profile after a reboot.

I've been around Linux/UNIX/BSD enough to not be surprised by the survival of the file system, but the unprompted reinstall is a mystery.

This message has been edited. Last edited by: striker1,

May have hit the "r" key on boot, or the system lost the boot drive and defaulted to the recovery partition.

Solved. Caused by a sneaky teenager.