What is vpsAdminOS
vpsAdminOS is a lightweight operating system that serves as a host for unprivileged Linux system containers. System containers run the entire userspace part of a Linux system and should look and feel as a virtual machine. You can create a container with many distributions, such as CentOS, Debian, Ubuntu and of course NixOS.
vpsAdminOS can be used as a live distribution and boot e.g. via network using PXE, or it can be installed to disk.
vpsAdminOS is built on top of Nix, NixOS and nixpkgs. Nix is a package manager, NixOS is a distribution based on Nix and nixpkgs is the package collection. We chose to make our own spin of NixOS, because NixOS relies on systemd and we wanted to replace it with something simpler. The host's only job is to mount storage, connect to network and run containers. systemd's advanced features are not needed, vpsAdminOS uses runit. This approach was pioneered by not-os, which we reused.
vpsAdminOS relies heavily on OpenZFS. The host system has no local state, but all containers and their configuration is stored on ZFS pools.
Containers in vpsAdminOS are managed by a system daemon called osctld -- short for OS control daemon. osctld can be controlled using a command line interface called osctl.
vpsAdminOS uses LTS Linux kernel with a mix of out-of-tree patches. These
patches are essential, providing e.g. a syslog namespace to isolate kernel logs,
virtualized views of selected files in
/sys and other tweaks.
Under the hood, osctld uses LXC to start and monitor the containers.
Container processes are also restricted by AppArmor.
vpsAdminOS is made for administrators. The people who have to get up during the night and deal with unexpected problems. It's designed to be hopefully simple and easy to debug. The boot process is made of several shell scripts, the few runit services are short scripts as well. We've invested a lot of time into making the administrator's life simpler, see the page about container administration. For example, although we have osctld to manage LXC seamlessly under the hood, LXC utilities are still easily accessible, so that osctld is not in the way while debugging issues.
vpsAdminOS is being developed and used in production by vpsFree.cz.
About the user guide
For the purposes of this user guide, you don't need to be familiar with Nix and NixOS, but it certainly helps. It's also good know the basics of ZFS -- e.g. what is a zpool, dataset, or a snapshot. To use vpsAdminOS in production, you definitely need to know how to use Nix with nixpkgs, NixOS. The learning curve is pretty steep, but we think it is well worth it.