Uhuh:
$ rm -rf /
rm: it is dangerous to operate recursively on '/'
rm: use --no-preserve-root to override this failsafeUhuh:
$ rm -rf /
rm: it is dangerous to operate recursively on '/'
rm: use --no-preserve-root to override this failsafe
That's a special case that is a) easy to call accidentally from a script when variables end up being unset and b) almost never a sensible thing to do.