[SOLVED] I used dd accidentally to restore a drive image over top of the drive I was presently using.
by wh33t from LinuxQuestions.org on (#6DY4N)
I have multiple linux installs on separate drives in my home computer. I have my main drive where I keep things tidy and stable and then I have an experimental copy of the main drive on a second drive. I also have a third drive which is just used as storage.
Often I will trial out experimental drivers, or attempt to write my own systemd service files etc on my experimental install, completely break it, and then reboot back into my main drive and use dd to overwrite the experimental drive with a disk image based upon my main drive.
Today I wasn't paying attention and from the experimental drive I used dd to overwrite itself. This process takes about 25 minutes and about 10 minutes in I realized I was in the wrong drive, but to my absolute surprise it still worked just fine. I saw the situation as an opportunity to see what would happen and was expecting the system to crash hard at some point, but it did not.
How is that possible that I can be overwriting a drive that I am presently booted into? Did it not crash or error in anyway because I wasn't presently using the system? It was just an idle desktop with a terminal window open running the dd command.
Often I will trial out experimental drivers, or attempt to write my own systemd service files etc on my experimental install, completely break it, and then reboot back into my main drive and use dd to overwrite the experimental drive with a disk image based upon my main drive.
Today I wasn't paying attention and from the experimental drive I used dd to overwrite itself. This process takes about 25 minutes and about 10 minutes in I realized I was in the wrong drive, but to my absolute surprise it still worked just fine. I saw the situation as an opportunity to see what would happen and was expecting the system to crash hard at some point, but it did not.
How is that possible that I can be overwriting a drive that I am presently booted into? Did it not crash or error in anyway because I wasn't presently using the system? It was just an idle desktop with a terminal window open running the dd command.