Read-only root

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I've been playing iwth using /dev/shm to create a read-only root.

Recompile the kernel to include /dev/shm support (look for virtual memory file system, tmpfs, shmfs or similar)

Then, add the following line to /dev/fstab:

tmpfs /var tmpfs defaults 0 0

You should have a virtual file system on /var. You can read and write to it, but on a reboot, everything will be wiped out.

The beauty is that you can create a tarball that you unpack on every reboot, and symlink the handful of files you may need to edit into it.

Unlike a ramdisk, you don't need to specify a fixed image size; the kernel will resize it as needed.