I keep /usr in a squashfs, mounted with aufs over top of it, for the 0.01% speedup I probably get (I grew up on gentoo, forgive me). Periodically, I need to re

I keep /usr in a squashfs, mounted with aufs over top of it, for the 0.01% speedup I probably get (I grew up on gentoo, forgive me). Periodically, I need to rebuild the squashfs to reclaim space in the aufs writable directory. I once had a script something like this: mksquashfs /usr /squashed/usr/usr_tmp.sfs -b 65536 umount -l /usr umount -l /squashed/usr/ro rm /squashed/usr/usr.sfs mv /squashed/usr/usr_tmp.sfs /squashed/usr/usr.sfs rm -rf /squashed/usr/rw/* mount /squashed/usr/ro mount /usr Guess what happens if you hit Ctrl-C during the mksquashfs? That's right, bash runs all the rest too, including the deletion of the old squashfs file. I was left without a /usr, and it was brutal. Managed to recover (it's incredible how resilient a linux system is, as long as /bin and /lib are intact), and immediately put "set -e" in almost every bash script on my machine (I also fixed the script to keep the system in a recoverable state at all times...).