@Viss my top tip on a Debian based system. Use debootstrap to install a minimal root folder onto tmpfs (eg in /run/ramdisk). Bind mount proc, says and dev into there and then chroot into it. Now you have a functioning shell which won't explode on you. Echo 'u' into proc sysrq-trigger to remount root read-only. Splat /dev/sda in relative safety. It's been a while since I actually did this at work but hopefully it still basically works. Luckily I can no longer remember WHY I did this. Hmm.