What to do when the system libraries go away…

You’ve been hacking away at this system (let’s be positive and upbeat and say it’s a test system and not production). Through a slip of the fingers, you move the system libraries out of the way – all of them. Now nothing can find the libraries. Now what? Is everything lost?

Don’t despair! You can do a lot without libraries. Already loaded software has the libraries in memory, so that is okay. This includes the shell, so the shell should be okay.

There may be some statically compiled binaries on the system that don’t require libraries; these can be run. If a scripting language like perl or ruby is statically compiled, then all is well – these languages can do anything, and can replace binaries (temporarily) such as mv, cp, and others. However, since vi is probably not statically linked, you may have to do it at the command line (and not in an editor).

Here are some things one can do:

echo *

Through the use of the shell’s filename expansion, this works out to a reasonable imitation of ls (ls -m, in particular). If you have to empty a file (make the contents nothing), use this command:

> file

Every standard utility today is dynamically linked; this means that in situations like these you are stuck with only what the shell itself provides. Remember that things like cat, ls, mv, cp, vi, rm, ln, and so on are all system executables – and quite possibly dynamically linked.

The best thing for a situation like this is to have prepared in advance – have a copy of busybox handy, and possibly a statically compiled perl or ruby (or both). Don’t forget editors – either have a copy of e3 or of a statically compiled editor. Busybox provides all the standard utilities in one statically created binary, and e3 is an editor that is tiny (and i386-specific) which emulates vi, pico, wordstar, and emacs (based on its name).  Neither busybox nor e3 require additional libraries.

A good tool (and a good tool in case of security breach) is a small CDROM of tools, all statically linked for your environment. Such a disk requires no libraries at all – and could have all of these necessary tools and more.

Of course, the best thing is to avoid doing this kind of thing in the first place…