Moving from CachyOS to NixOS

nixos-anywhere installs NixOS from the MacBook over SSH. It switches the running CachyOS into a NixOS installer in RAM (kexec), wipes the NVMe drive and lays it out as hosts/desktop/disko.nix says, builds the system on the desktop itself and reboots into it. No USB stick, and nothing Linux gets built on the Mac.

CachyOS and everything on the NVMe drive are gone afterwards. Your home folder is backed up to the Kingston SATA SSD (sda) first, and only what restore-filter lists comes back: it's a fresh start. The other SATA SSD (sdb) is never touched.

1. On the desktop (CachyOS)

• Optional, but the last chance: record WoW's performance to compare later. In Faugus, edit Battle.net, turn on MangoHud and add this line to the launch arguments: MANGOHUD_CONFIG=read_cfg,output_folder=/home/vizie/benchmarks,log_duration=60,log_interval=0. In game, stand somewhere you can return to (a busy city), keep the camera still and press Left Shift+F2. Do it three times. Do the same on NixOS later and compare with ~/git/dot/tools/bench-compare.

• Quit Signal, Discord, Firefox, Claude and the games, then update the backup (only what changed since the last run is copied):

  sudo ~/git/dot/tools/backup-to-sata

2. On the Mac

Needs Nix (with flakes) and the GitHub CLI signed in to your account: dot and philly are private, and gh auth setup-git lets Nix fetch them. The Mac's public key must also be in macKeys in hosts/desktop/default.nix (committed and pushed), so it can log in to the new system.

gh auth setup-git
gh repo clone Eiziv/dot ~/dot
cd ~/dot && nix develop

nix develop opens a shell with nixos-anywhere in it. Then install. It logs in as you (with your password, or the Mac's key if CachyOS has it), asks for your sudo password once, and from then on wipes the desktop's NVMe drive without asking again:

nixos-anywhere --flake .#desktop --build-on remote --copy-host-keys --no-use-machine-substituters vizie@10.0.0.40

It takes a while: the CachyOS kernel's binary cache has been down, so the kernel compiles on the desktop. --no-use-machine-substituters skips that cache; if it's back up (curl -sI https://attic.xuyh0120.win/lantian/nix-cache-info gives 200), leave the flag out and the kernel downloads instead. The desktop reboots into NixOS at the end.

If the kernel compile fails with a "Bus error", the installer ran out of RAM (it builds there). The backup drive has the system that was built on CachyOS, kernel included. Load it into the new system's store and run only the install:

ssh root@10.0.0.40 'mkdir -p /backup && mount -o ro /dev/disk/by-label/backup /backup &&
  nix --extra-experimental-features nix-command copy --no-check-sigs \
    --from file:///backup/nix-cache --to /mnt "$(cat /backup/nix-cache/system)"'
nixos-anywhere --flake .#desktop --build-on remote --copy-host-keys --no-use-machine-substituters --phases install,reboot root@10.0.0.40

3. After the reboot

The desktop may come back on a different IP address (it did: 10.0.0.127). If ssh times out, find it in the router's client list, or scan for the desktop's host key: ssh-keyscan -t ed25519 10.0.0.<n> and compare with ssh-keygen -F 10.0.0.40. A DHCP reservation in the router keeps it fixed.

From the Mac (its key is in the config, for root and for you). The backup drive is mounted read-only at /mnt/backup:

ssh root@10.0.0.127
passwd vizie
/mnt/backup/vizie/git/dot/tools/restore-from-sata

Then log in on the desktop.

4. On the new system

• The login screen is the same gtkgreet over the blurred wallpaper.
• Only what restore-filter lists came back: app data and logins, SSH keys, shell history, ~/git/dot, Steam's settings and saves. Everything else (Downloads, the other repos, CachyOS leftovers) is on the backup drive, at /mnt/backup/vizie/, to copy something back.
• "Command not found" suggestions need nix-index's database once: nix-index (takes a few minutes).
• Check the background programs: systemctl --user list-units --type=service.

5. What changed

What is different from CachyOS, all on purpose:

• Packages are generic x86-64 builds, apart from the kernel (Zen 4) and proton-cachyos (x86-64-v3). CachyOS rebuilds everything for v3/v4.
• Snapper root snapshots are replaced by NixOS generations: each rebuild is a boot menu entry. /home was never snapshotted on CachyOS either.
• GTK theme: set in modules/home/theming.nix. nwg-look can't save over those files any more.
• Signal theme is built into the package: edit, rebuild, config/signal/restart.
• Bitwarden autostart: the same XDG autostart entry, with NixOS's program name.
• fish: only CachyOS's default fish config was there, and your shell is zsh, so fish isn't set up.
• vkBasalt's ReShade shaders in ~/.config/vkBasalt/reshade-shaders stay in your home folder; they aren't in this repo (vkBasalt.conf doesn't use them).
• vkSumi: its config is kept, but the layer itself wasn't installed on CachyOS (there is no nixpkgs package for it either).

Unchanged on purpose, but worth knowing:

• kitty's font: kitty.conf asks for JetBrains Mono, which was never installed, so kitty has been showing Noto Sans Mono. That's kept. Add nerd-fonts.jetbrains-mono to fonts.packages in modules/nixos/desktop.nix to get the font the config names.
• The login screen opens a kitty terminal behind gtkgreet (hl.exec_cmd("kitty") in config/greetd/hyprland.lua), running as the greeter user. If gtkgreet ever crashed, that shell would be on screen before anyone logs in. If it's a leftover from debugging, delete that line.
• ~/.ssh/authorized_keys has a key labelled chris@echoz.io, which lets that key log in as you over SSH (port 22 is open, as before). It stays in your home folder.
• mDNS (port 5353) stays closed in the firewall, as ufw had it.
• sched-ext schedulers stay off, as before. See the comment in modules/nixos/cachyos.nix to try one.

6. Games

• Steam: your settings, Proton versions and game saves (compatdata) are back. The games in ~/Games/SteamLibrary and Steam's own library show as not installed; install them again. Steam may need the library folder re-added (Settings → Storage).

• WoW: in Faugus, remove the old Battle.net entry and add Battle.net again (Faugus installs it into a new prefix at ~/Games/battlenet). Pick the same runner, Proton-CachyOS Latest (it's back in ~/.local/share/Steam/compatibilitytools.d), and the same launch arguments: WINE_SIMULATE_WRITECOPY=1 and PROTON_ENABLE_WAYLAND=0. Install WoW, then copy your settings and addons back before you start it:

  cp -a /mnt/backup/wow/{WTF,Interface} ~/Games/battlenet/drive_c/'Program Files (x86)'/'World of Warcraft'/_retail_/

• OSRS: install the official Old School RuneScape launcher. Bolt is gone, and so is its data.

7. Once you're happy

The backup on the Kingston drive stays until you need the drive for something else. It is the only copy of what wasn't restored, including the repos that exist only here (skate3, skate-game, he60, move, and Left4Resi's uncommitted changes), so copy out anything you want before reusing the drive. NixOS mounts it read-only at /mnt/backup; before reusing it, remove the fileSystems."/mnt/backup" entry in hosts/desktop/hardware-configuration.nix.