Raspberry Pi murder

By Abhijit Menon-Sen <ams@toroid.org>

2017-01-19

I wanted to restore a clean Raspbian image on the Raspberry Pi that was running in the battery room. I could have gone and got it, but I would have had to climb a ladder.

So I thought “Why not just remount the filesystems 'ro' and dd the image to /dev/mmcblk0?”

I remounted / and /boot (after "systemctl isolate rescue.target", which stopped sshd but left my ssh session running) read-only, and dd'ed the image from an NFS mount onto /dev/mmcblk0. The dd worked fine. I used /proc/sysrq-trigger afterwards to sync and reboot (I couldn't run any binaries after the dd, which wasn't much of a surprise). The machine fell off the network as expected…

…and never came back up. So I climbed up the ladder and brought the Pi down to my desk and plugged it into my monitor. It did start to boot, and got a fair distance before the kernel panicked. I didn't bother to try to figure out the problem, just extracted and rewrote the SD card; and all was well thereafter.

But I still think my plan ought to have worked.