# 0016: Arch Linux base, in snapshots

> Why WolOS is built on Arch Linux packages pinned to a dated snapshot.

Source: https://wolos.pages.dev/manual/adr-0016

## Context

the desktop needs current GPU drivers (Mesa, NVIDIA, virtio-gpu in VMs), native Steam and Proton, and a current kernel. A rolling base breaks the "it just works" promise; a frozen base ages.
## Decision

- Base = Arch Linux packages pinned to one Arch Linux Archive date per WolOS release (`wolos-iso/profile/snapshot`). pacman reads only that date (`Server = https://archive.archlinux.org/repos/<date>/$repo/os/$arch`). A WolOS update moves the whole system to a newer tested date; nothing rolls in between.
- Kernel = only `linux-wolos`, published through the `[wolos]` channel: github.com/wonderlandos/linux (current stable, pinned ref) + `kernel/conf/wolos.config` fragment + the patches in `kernel/linux/patches/`. Other or modified kernels may be installed with pacman; they get their own boot entry, `linux-wolos` stays the default.
- A/B slots: btrfs root subvolumes `@wolos-a` / `@wolos-b` (writable, so pacman works), shared `@home`, `@var`. An update snapshots the running root into the other slot, moves its pacman.conf to the new release date, runs `pacman -Syu` there and boots it next; user-installed packages carry over. systemd-boot entries with boot counting (`+3`) fall back to the previous slot, which is also the restore point. A failed update deletes the new slot.
- Init = systemd. rc.d scripts become units in `image/files/usr/lib/systemd/`. sysctl/pciconf/kld readers become /proc, /sys, `lspci`, modprobe.
- Build: `wolos-iso/build.sh` = mkarchiso profile `wolos-iso/profile/` (live + installer ISO) on any Arch host or `archlinux` container. VM tests use QEMU virtio-gpu, so Hyprland runs in the VM.
- Packages: pacman stays the package manager, used directly; `wol` controls only the pinned pacman.conf, release updates and `.wol` app metadata. `.wol` = signed pacman package + WolOS metadata; `[wolos]` repo (apps, kernel, system) beside the pinned Arch repos; each release has a signed manifest (snapshot date, repo revision, image + sha256).
- Steam and Proton are native packages (multilib). NVIDIA uses `nvidia-open`.
## Consequences

FreeBSD-only code (ZFS boot environments, pf, bsdinstall, pkg, wolos_qos kmod) is replaced; `Host::is_freebsd` paths stay compiling only while removed slice by slice. Firewall = nftables. Scheduler QoS moves to a sched_ext scheduler (follow-up).