Moving from CachyOS to NixOS

The install wipes the whole NVMe drive (nvme0n1, the 980 PRO) and lays it out again with disko, as hosts/desktop/disko.nix describes. CachyOS and everything in it are gone afterwards, so your home folder goes to the Kingston SATA SSD (sda) first and comes back after the install. Game installs aren't backed up (see backup-filter): Steam games and WoW download again. WoW's settings and addons are kept.

The other SATA SSD (sdb) isn't touched at any point. disko only knows the NVMe drive, by its serial number.

1. Before you start (on CachyOS)

• Push this repo and the latest Eiziv/philly.
• Get the NixOS installer (26.05, minimal is enough) on a USB stick, and make sure Secure Boot is off in the firmware, as it is for Limine now.
• Optional, but this is the last chance: record WoW's performance on CachyOS, to compare with NixOS 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. The logs land in ~/benchmarks, which the backup includes. Do the same on NixOS later, then compare the two with ~/git/dot/tools/bench-compare.

The backup can be made ahead of time, days before the install if you like. Right before the wipe you run the two rsync commands below again (and the "save the built system" step, if the config changed since); they only copy what changed, so that takes a minute or two.

tools/backup-to-sata does all of the steps below in one go (run it with sudo; it only formats the Kingston if it is empty). They are spelled out here too, in case you'd rather do them by hand.

Prepare the backup drive (once). This erases sda, the 112 GB Kingston, which is empty now. Check that the name points at sda first:

ls -l /dev/disk/by-id/ata-KINGSTON_SA400S37120G_50026B76820FD3CE
sudo mkfs.btrfs -L backup /dev/disk/by-id/ata-KINGSTON_SA400S37120G_50026B76820FD3CE
sudo mkdir -p /mnt/backup
sudo mount -o compress=zstd /dev/disk/by-label/backup /mnt/backup
sudo install -d -o vizie /mnt/backup/nix-cache /mnt/backup/wow

Save the built system. The finished system and the disko script go onto the backup drive, so the installer doesn't have to build anything (or compile the CachyOS kernel, if its binary cache is still down):

cd ~/git/dot
sys=$(nix build --no-link --print-out-paths .#nixosConfigurations.desktop.config.system.build.toplevel)
disko=$(nix build --no-link --print-out-paths .#nixosConfigurations.desktop.config.system.build.diskoScript)
nix copy --to 'file:///mnt/backup/nix-cache?compression=zstd' "$sys" "$disko"
echo "$sys" > /mnt/backup/nix-cache/system
echo "$disko" > /mnt/backup/nix-cache/disko

Back up WoW's settings and addons (WTF is keybinds, macros and addon settings, Interface is the addons):

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

Back up your home folder. Quit Signal, Discord, Firefox, Claude and the games first, so their databases aren't copied halfway through a write. About 83 GB before compression, and the saved system adds roughly 10 GB, so it fits the 112 GB drive with some room. If it runs out of space, leave out repos that are pushed to GitHub (the biggest are git/skate3, 23 GB, and git/philly, 16 GB) with an extra --exclude=/git/skate3/:

sudo rsync -aHAXx --delete --info=progress2 --filter='merge /home/vizie/git/dot/backup-filter' /home/vizie/ /mnt/backup/vizie/

Check that it looks complete (ls -a /mnt/backup/vizie, du -sh /mnt/backup/*), then sudo umount /mnt/backup. To update the backup later, mount it again (sudo mount -o compress=zstd /dev/disk/by-label/backup /mnt/backup) and rerun the commands above.

2. Install

Boot the installer. Wired network works out of the box; the install itself doesn't need it.

sudo -i

# The backup drive, read-only. Not under /mnt: disko unmounts everything there.
mkdir /backup
mount -o ro /dev/disk/by-label/backup /backup
sys=$(cat /backup/nix-cache/system)
disko=$(cat /backup/nix-cache/disko)

# The disko script. It doesn't ask before it wipes, so check that the drive it
# names is the 980 PRO (nvme0n1) one last time.
ls -l /dev/disk/by-id/nvme-Samsung_SSD_980_PRO_1TB_S5GXNF1R877751D
nix --extra-experimental-features nix-command copy --no-check-sigs --from file:///backup/nix-cache "$disko"

# Wipe, partition, format and mount the NVMe drive at /mnt.
"$disko"

# Copy the system onto it and install it, with the boot loader.
nix --extra-experimental-features nix-command copy --no-check-sigs \
  --from file:///backup/nix-cache --to 'local?root=/mnt' "$sys"
nixos-install --system "$sys" --no-channel-copy
# It asks for a root password at the end.

# Your home folder back, owned by you (uid 1000, group users).
rsync -aHAX --info=progress2 --chown=1000:100 /backup/vizie/ /mnt/home/vizie/
nixos-enter --root /mnt -c 'passwd vizie'
reboot

If something in /backup/nix-cache is missing, install from the flake instead (this needs the network, and compiles the kernel if its cache is down): nixos-install --flake /backup/vizie/git/dot#desktop after nix run github:nix-community/disko/latest -- --mode destroy,format,mount /backup/vizie/git/dot/hosts/desktop/disko.nix.

3. First boot

• The login screen is the same gtkgreet over the blurred wallpaper.
• Home Manager replaces the old symlinks in ~/.config (pointing into ~/git/dotfiles) with its own. The old ones are kept beside them with a .pre-nixos suffix, so nothing is overwritten.
• Bolt installs from Flathub in the background on the first boot with network (systemctl status flatpak-bolt).
• "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.

4. 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.

5. 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:

  sudo mount -o ro /dev/disk/by-label/backup /mnt
  cp -a /mnt/wow/{WTF,Interface} ~/Games/battlenet/drive_c/'Program Files (x86)'/'World of Warcraft'/_retail_/
  sudo umount /mnt

• OSRS: Bolt installs itself again (see First boot); its data in ~/.var/app/com.adamcake.Bolt came back with your home folder, so you stay signed in.

6. Once you're happy

The backup on sda stays until you need the drive for something else. NixOS doesn't mount it; sudo mount /dev/disk/by-label/backup /mnt gets you into it.