I’ve found ttylinux to be quite useful. For a while it was not actively maintained, but now Douglas Jerome has stepped up as the new maintainer. It’s a small, fast text based Linux distribution that is an invaluble part of my usb toolkit. It can mount a usb drive, giving quick access to be able to modify important files.
Nicely, while ttylinux is only ~10 megabytes, it has bash, the most used shell, rather than a smaller alternative. I’ve added in nano, an editor that I prefer to vi.
The default login is “root” password “root” or “guest” “guest”. Ttylinux loads its entire filesystem as an initial ram disk (initrd). The filesystem is easily modified (It’s a loopfile), but the bundled applications are fairly good. You can munt (and then modify) the entire system in an existing Linux install:
mkdir mount