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feat(nixos): prune system+HM gens after 14d, keep ≥3 past (#128 )

Weekly nomarchy-gen-prune deletes only generations that are both older
than 14 days and beyond the three most recent past gens (current always
kept), for system and Home Manager profiles. Stock nix.gc no longer uses
--delete-older-than. checks.gen-prune covers selection self-test and
unit wiring; doctor points at the new tool when disk is tight.

2026-07-15 11:59:26 +01:00

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Recovery runbook — when something breaks

Ordered from "the desktop looks wrong" to "the machine won't boot". Everything here already ships on an installed machine — you don't need a live USB until the last resort. The theme is always the same: nothing in Nomarchy is destroyed by a bad change — every rebuild is a NixOS / Home Manager generation you can step back to, and (on BTRFS installs) snapper keeps file-level history on top.

If the graphical session is unusable, a text console is one keystroke away: Ctrl+Alt+F2 gives a TTY login (the session itself runs on tty1); log in with your normal user.

1. A theme or desktop change broke the session

Theme applies and home-update are Home Manager switches — one generation each, so the previous desktop is still on disk:

home-manager generations          # newest first, one per theme/HM change
/nix/store/…-home-manager-generation/activate   # run the one you want

The same picker lives in the menu: System › Recovery › Desktop generation lists the recent Home Manager generations — pick one and it activates. System-level undo is System › Recovery › System boot generation (boot menu) or Files (BTRFS) (snapper).

Or simply apply a theme you know is good: nomarchy-state-sync apply boreal (or any preset). If a switch failed halfway, the state file is written before the rebuild — fix the cause and re-run home-manager switch --flake ~/.nomarchy (or nomarchy-home).

Your flake checkout is a git repo, and with auto-commit enabled every apply is a commit — and every nomarchy-pull/-rebuild/-home first sweeps pending hand edits into one, so history mirrors your generations: git -C ~/.nomarchy log to see what changed, git revert the culprit, then nomarchy-home.

2. The desktop won't start at all

Greeter loops, black screen after the password, session exits straight back to tuigreet — from the Ctrl+Alt+F2 TTY:

journalctl -b -u greetd           # did the session command launch?
journalctl --user -b              # Hyprland + the user services

Rolling back the desktop half is §1 (works from the TTY).
If greetd/tuigreet itself is broken, that's system-side → §3.
In a VM, a black screen is almost always missing guest OpenGL, not your config — see docs/TESTING.md §5.
First boot after an install came up unthemed: read /var/log/nomarchy-hm-preactivate.log on the installed system.

3. A system change broke it — boot an older generation

Reboot and pick an older NixOS generation in the systemd-boot menu (hold a key during firmware handoff if the menu doesn't linger; the last 10 generations are kept). That boots yesterday's system unchanged.

Booting an old generation is temporary — the default entry is still the broken one. Make the fix stick from the working boot: revert the change in ~/.nomarchy (git -C ~/.nomarchy revert … or edit system.nix back), then nomarchy-rebuild.

Automatic prune (#128): a weekly timer (nomarchy-gen-prune) removes system and Home Manager generations that are older than 14 days and beyond the three most recent past gens (current + ≥3 past always kept). Manual: sudo nomarchy-gen-prune (or --dry-run).

4. Files went missing or wrong — snapshots (BTRFS installs)

With nomarchy.system.snapper.enable (the installer's default on BTRFS), the root filesystem has hourly/daily history, and nixos-rebuild-snap leaves a snapshot right before a rebuild:

GUI: menu › System › Recovery › Files (BTRFS) (btrfs-assistant; expects a polkit password prompt).
Terminal/SSH: sudo nomarchy-snapshots — browse a snapshot's diff, restore changed files (snapper undochange), or roll the whole root back to a snapshot and reboot. Both destructive actions sit behind a typed-yes confirmation.

Snapshots are the undo for data on disk; the Nix config model is undone by generations (§1/§3) — use each for its half.

5. Last resort — from the outside

Boot the Nomarchy ISO (any NixOS ISO works), then:

sudo mount /dev/<root> /mnt        # + /mnt/boot; LUKS: cryptsetup open first
sudo nixos-enter --root /mnt       # chroot with nix available

From there you have the full toolbox: nixos-rebuild boot --flake /home/<you>/.nomarchy#default after fixing the flake, or snapper from §4. If you get this far with something Nomarchy shipped broken, please file it.

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