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.

> control/configuration/debugging

This is one of several major arguments made against unikernels in that famous Triton rant from a decade ago:

https://tritondatacenter.com/blog/unikernels-are-unfit-for-p...

Basically, even if your application _can_ run as the kernel, and it's desirable for it to run with kernel-level permissions, do you really want production to be a world without strace and iotop and the like?

That's a halted firewall setup. Normally as part of shutdown you would tear down networking in SysVinit or systemd but you don't actually have to do that. When shutting down you can choose whether to power off or just to halt. It's basically like the old Windows "It is now safe to power off your PC".