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steamify-cachyos-dev/.claude/skills/wsl-build-host/SKILL.md
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theupriser cb247b9cc3 docs: wsl-build-host skill, vminstall.sh without udisks (WSL), AGENTS.md/TODO WSL notes corrected
The WSL box has a desktop after all (WSLg windows on Windows), closing the
Arch window shuts it down, and vminstall.sh loop-mounts the ISO with losetup
as root when udisksctl is missing (R1c).
2026-09-29 15:40:03 +02:00

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---
name: wsl-build-host
description: Use when building or testing the Steam Machine ISO, or running the VM tests (vmtest.sh), on the user's Windows PC - Arch Linux in WSL2 (`ssh wsl`), with podman, QEMU + KVM and WSLg windows on the Windows desktop. Covers access, syncing working trees from the laptop, the podman ISO build as root, VM windows vs headless, showing output in the user's WSL terminal, and the WSL pitfalls (closing the window kills it, no udisks, no GPU passthrough).
---
# WSL build host (Arch on WSL2, the Windows PC)
The laptop is an arm64 Mac: x86_64 QEMU or containers there run emulated,
far too slow for Plasma/Calamares or an ISO build. The PC is the x86 host:
same workflows as `steam-machine-iso`, `vm-install` and `vmtest.sh`, with
the differences below. Found and tried on 2026-09-28 (ISO build, ISO VM with
a window, the loop-mount fallback); `vmtest.sh` itself not yet run here.
## Access
- `ssh wsl` = `root@10.0.0.36`, port 22 (alias in the laptop's
`~/.ssh/config`). That's Arch's own sshd inside WSL, not Windows' OpenSSH.
- `%UserProfile%\.wslconfig`: `networkingMode=mirrored` (WSL shares the PC's
LAN IP), `nestedVirtualization=true` (`/dev/kvm`), `memory=` (WSL2 defaults
to half the RAM: 30 GB seen). `/etc/wsl.conf`: `[boot] systemd=true`.
- Installed: podman, qemu-full, edk2-ovmf (`/usr/share/edk2/x64/OVMF*.4m.fd`,
run.sh finds it), git, rsync, python, python-pillow (`qmpshot.py` writes a
.ppm without it). vmtest.sh also wants `screen`.
- **The Arch window must stay open.** Closing the last WSL terminal shuts
the distro down a little later, with every build, VM and sshd in it: SSH
times out while the PC still pings. Ask the user to keep it open during
runs and to reopen it after a Windows reboot. After such a restart, delete
half-written VM disks before rerunning (`vminstall.sh` refuses an
existing `disk.qcow2`, and `--force` asks).
## Differences from a normal Linux host
- User is **root**: no `sudo`, `systemd-run` without `--user`, paths under
`/root/projects/` and `/root/vms/`. Units have no `$HOME`: set `HOME=/root`
for scripts started with `systemd-run` (vminstall.sh needs it).
- No udisks: `vminstall.sh` falls back to `losetup -P` + `mount` when
`udisksctl` is missing and it runs as root. Don't install udisks2 here.
- `pkill -x qemu-system-x86_64` never matches (names over 15 characters):
`pkill -f '^[q]emu-system'`.
## Getting the code there
The WSL clones have no GitHub key: sync the laptop's working trees
(uncommitted changes included) instead of pulling. `vmtest-remote.sh`
pulls the pushed branch on the remote, so it needs a GitHub key there first
(and `REMOTE_REPO=/root/projects/steamify-cachyos-dev`).
```bash
cd ~/Projects && rsync -az --exclude out --exclude build \
steammachine-cachyos-live-iso steamify-cachyos steamify-cachyos-dev wsl:projects/
ssh wsl 'find ~/projects -name __pycache__ -prune -exec rm -rf {} +; chown -R root: ~/projects'
```
Both fixups are needed: rsync keeps the laptop's uid (git then refuses with
"dubious ownership"), and a synced `patches/__pycache__` breaks
`steamify-prepare.sh` ("Is a directory").
## Building the ISO (~8 minutes)
```bash
ssh wsl 'cd ~/projects/steammachine-cachyos-live-iso && ./steamify-prepare.sh ~/projects/steamify-cachyos'
ssh wsl 'cd ~/projects/steammachine-cachyos-live-iso && rm -rf build out && systemd-run --collect -q -u isobuild-$(date +%s) --working-directory=$PWD bash -c "podman run --rm -t --pids-limit=-1 --ulimit nofile=65536:65536 --privileged --network=host -v /root/projects/iso-cache:/var/cache/pacman/pkg -v $PWD:/iso -w /iso docker.io/cachyos/cachyos:latest bash -c '\''pacman-key --init && pacman-key --populate && pacman -Syu --noconfirm --needed archiso mkinitcpio-archiso git squashfs-tools grub sudo && ./build-live-modules.sh && ./build-calamares-modules.sh && { ./buildiso.sh -p desktop -w || ./buildiso.sh -p desktop -c -w; }'\'' > /root/projects/iso-build.log 2>&1"'
```
Wait in one background command, not a polling loop:
`ssh wsl 'until ! podman ps -q | grep -q .; do sleep 20; done; tail -c 1500 ~/projects/iso-build.log; ls -la ~/projects/steammachine-cachyos-live-iso/out/desktop/'`.
Never start a build while `podman ps` shows one. Output:
`/root/projects/steammachine-cachyos-live-iso/out/desktop/*.iso` (from
Windows Explorer: `\\wsl$\<distro>\root\projects\...`). The trailing
`chown: missing operand` / "unknown error" is harmless. mksquashfs shows no
progress in the log; the growing `build/iso/arch/x86_64/airootfs.sfs`
(~3.1 GB when done) is the measure.
## VM windows on the Windows desktop (WSLg)
There is a desktop after all: WSLg (`/tmp/.X11-unix/X0`,
`/mnt/wslg/runtime-dir/wayland-0`) puts QEMU's GTK window on the user's
Windows desktop. SSH sessions and units lack the variables, so set them:
`DISPLAY=:0 WAYLAND_DISPLAY=wayland-0 XDG_RUNTIME_DIR=/mnt/wslg/runtime-dir`.
- A VM for the user to watch or drive: that env plus e.g.
`VM_SERIAL=/root/vms/iso-vm/serial ISO_VM_DIR=/root/vms/iso-vm scripts/vmisoboot.sh --fresh --iso <iso>`.
The user may click through it themselves: check the disk size / serial
log before assuming it still sits at the live session.
- Automated runs stay headless (`--headless` / `VM_HEADLESS=1`, vmtest.sh's
default); `qmpshot.py` works then.
- GPU: no passthrough of the NVIDIA card. WSL2 only has the paravirtual
`/dev/dxg`, no PCI device for VFIO, and Windows keeps driving the card.
run.sh's default virgl (`virtio-vga-gl`, `gl=on`) renders through WSLg's
d3d12 Mesa on it, but QMP screenshots then give "no surface".
## Showing output in the user's WSL terminal
Their visible terminal is the `-bash` whose parent is WSL's `/init`
(`ps -eo pid,ppid,tty,args --forest`), usually `/dev/pts/0`. Not the
`login -- root` one: a hidden console getty. Stream a log into it as a unit
so it can be stopped:
`systemd-run --collect -q -u showlog bash -c "tail -n 20 -F <log> > /dev/pts/0 2>&1"`;
stop with `systemctl stop showlog` (Ctrl+C there doesn't). Tell the user
not to type there while it runs. A header printed before a busy log scrolls
away at once.