IIRC, it ran a script as init process that set up the network cards, set up iptables, etc. and then just exited. Kernel would panic (the "init was killed" panic), but the network would still be functional. Automatic reboot on panic was disabled.

To reconfigure, the admin would simply reset it and start the system with "init=/something/else" as kernel parameter that booted to a normal userspace.

Oh, clever; I didn't know you could make Linux panic but keep running.