Suppose -- arbitrarily and entirely theoretical, of course -- that you wish to replace the currently used /lib/libc.so file. Considering that you might be using -- further absurdely and entirely theoretical, of course -- cp(1), itself dynamically linked. It might well happen, that during the copy process, you loose, as cp(1) might fail and thus won't finish the copy. In theory.
Now should this happen, you need to get a proper libc back into your filesystem. You can do this remotely (if you have remote console access) on your trusty old NetBSD system by booting into single user mode. Or can you? As you boot, you will find that the dynamically linked /sbin/init will also fail...
Ask the bootloader to prompt you for the path to init by passing '-a' to the boot command (so together with single-user mode this would be 'boot -as'). Then pass it /rescue/init as the path to init and /rescue/sh as the shell. From there, you can fix your system via the other commands found statically linked in /rescue. Which is exactly why they call it that.
November 30, 2005