# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Flake-based NixOS config for a homelab. Hosts: **jupiter** (ZimaBlade NAS, x86_64),
**neptun** (netcup public reverse proxy + tailnet node, x86_64), **mercury** (Raspberry
Pi 3B+ DNS/DHCP, aarch64). See `README.md` for the full install/deploy walkthrough.

## Layout

```
flake.nix          # nixosConfigurations: real hosts + test/util targets
common.nix         # shared base: user darman (key-only ssh), nix settings, firewall :22, tz
services/<cat>/*.nix   # one reusable NixOS module per service, grouped by category
                       # (media, network, vpn, identity, dev, desktop); each opens
                       # ITS OWN firewall ports. services/containers.nix (podman
                       # backend) stays at the top level, shared across categories.
hosts/<h>/         # configuration.nix + disk-config.nix (disko) + hardware-configuration.nix + secrets.nix
secrets/<h>.yaml   # sops-nix, age-encrypted per host
scripts/deploy     # config-agnostic deploy wrapper (all args mandatory)
scripts/edit_secrets
.sops.yaml         # per-host encryption rules (admin key + each host's key)
```

A host = `common.nix` + the `services/**` modules it imports + its `hosts/<h>/configuration.nix`.
`services/` modules are engine-agnostic and shared across hosts (e.g. `services/vpn/tailscale.nix`,
`services/network/caddy.nix` used by jupiter and neptun).

## Commands

Eval/verify a config before deploying (eval only checks the module tree, not
freeform config like pihole's TOML or a container's runtime):
```
nix eval --raw .#nixosConfigurations.<host>.config.system.build.toplevel.drvPath
```

Deploy (from a non-NixOS laptop too — runs nixos-rebuild/nixos-anywhere via `nix run`):
```
./scripts/deploy switch  <config> <host>     # daily rebuild + activate
./scripts/deploy install <config> <host>     # first install (nixos-anywhere, wipes OS disk)
./scripts/deploy kexec   <config> <host>     # RO-root box (ZimaOS): kexec into a RAM installer first
sudo ./scripts/deploy kexec-local [--yes]    # kexec THIS box (no ssh); confirm prompt unless --yes
./scripts/deploy image   mercury             # build the aarch64 SD image
./scripts/deploy flash   mercury /dev/sdX    # build + write SD + drop the sops age key
```

Both password prompts are auto-filled from the "HomeLab" Proton Pass vault, keyed by
**`<config>`, not `<host>`** — items `darman@<config>` (sudo) and `root@<config>` (ssh).
A *trashed* Proton Pass item with the same title shadows the active one and yields an
empty password, so the script resolves the title among `--filter-state active` items
first; a plain `pass-cli item view --item-title` silently returns the trashed copy and
you get an interactive prompt with no explanation.

`HOMELAB_KEXEC_TARBALL` (+ `_CPIO` / `_GZIP`) makes `kexec`/`kexec-local` reuse a
prebuilt installer instead of rebuilding ~500MB. The VM test below uses this.

Secrets (needs the admin age key at `~/.config/sops/age/keys.txt`):
```
./scripts/edit_secrets secrets/<host>.yaml
```

Test a service config BEFORE touching hardware — always do this for nontrivial changes:
```
# x86 QEMU VM of mercury's DNS/DHCP stack (fast; validates pihole/unbound at runtime)
nix build .#nixosConfigurations.mercury-vm.config.system.build.vm -o result
./result/bin/run-mercury-vm-vm            # ssh -p 2223 darman@localhost (pw: test)
# jupiter services as a VirtualBox OVA
nix build .#nixosConfigurations.jupiter-vbox.config.system.build.virtualBoxOVA
# end-to-end VM test of `deploy kexec-local` (~45s once the tarball is built)
nix build .#checks.x86_64-linux.kexec-local -L
```

`checks.kexec-local` is the only way to exercise `kexec-local` at all: it jumps the
machine you are typing at, so it cannot be rehearsed on real hardware and a failure
looks exactly like a slow boot. It asserts the box actually left the old kernel
(SSH drops then returns), came back as `nixos-installer`, lost its old `/run`, and
kept its ssh host key. Run it after ANY change to the kexec paths.

## Secrets (sops-nix)

- Each `secrets/<host>.yaml` is encrypted to the **admin** key (edit) + that **host's**
  key (runtime decrypt); rules in `.sops.yaml`. Private keys live OFF-repo:
  `~/.config/sops/age/keys.txt` (admin), `~/.config/homelab/<host>/` (host keys).
- jupiter/neptun decrypt with their **ssh host key** (`ssh-to-age` recipient), shipped at
  install via `nixos-anywhere --extra-files`.
- mercury (SD image, no `--extra-files`) uses a **dedicated age key** at
  `/var/lib/sops-nix/age.txt` — `./scripts/deploy flash` writes it to the ext4 root partition.
- A service password that must come from sops but whose module has no `passwordFile`
  hook (pihole, adguard) is injected via `sops.templates` → an env file → the service
  (`FTLCONF_*` for pihole). See `hosts/mercury/configuration.nix`.

## Non-obvious gotchas (all learned the hard way)

- **aarch64 (mercury)**: the x86 laptop needs `extra-platforms = aarch64-linux` in
  `/etc/nix/nix.custom.conf` (NOT `/etc/nix/nix.conf` — Determinate Nix regenerates that)
  + `qemu-user-static-binfmt`, else emulated builds fail with "platform mismatch". Or
  build on the Pi with `--build-host darman@<ip>`.
- **pihole on mercury is a CONTAINER** (`services/network/pihole.nix`, official image, host
  networking, caps NET_ADMIN/NET_RAW/SYS_NICE/CHOWN, `FTLCONF_*` env config). The native
  `services.pihole-ftl` module **segfaults on the Pi 3B+ aarch64** — do not switch back.
- **`services.unbound.resolveLocalQueries = false`** is required: unbound listens on
  :5335, so leaving it true points the host's resolv.conf at 127.0.0.1:**53** with nothing
  there → boot-time DNS deadlock (starves image pulls / list downloads). Host resolves via
  upstream `networking.nameservers`; pihole forwards to unbound explicitly at `127.0.0.1#5335`.
- **Remote deploy pushes unsigned closures**: hosts set `nix.settings.trusted-users =
  [ "root" "@wheel" ]` (in common.nix) so a laptop-built closure is accepted by the target.
- **jupiter**: `boot.kernelParams = [ "reboot=pci" ]` (warm reboot hangs on that board);
  eMMC initrd modules pinned in `configuration.nix` (generate-config misses them); the
  16TB×2 **RAID0** data lives on `/mnt/data` with `nofail`, kept OUT of disko (never wiped).
- **terra: `./scripts/deploy kexec-local` hangs hard — do not use it there.** Confirmed
  on real hardware: kexec's `device_shutdown()` pass runs (SCSI disks sync fine in the
  log), then the machine goes dark and never comes back — `journalctl --list-boots`
  showed a ~15min gap before the next boot, i.e. a genuine hang needing a manual power
  cycle, not a slow jump. Near-certainly amdgpu (RX 6800 XT): discrete AMD GPUs are known
  to hang during kexec's device-shutdown pass with no clean handoff before the jump —
  same class of issue as jupiter's `reboot=pci` workaround, just fatal here instead of
  slow. Use the USB installer path instead (README's "First install on terra" section).
- **disko wipes only the OS disk** named in `hosts/<h>/disk-config.nix`; data disks are
  plain `fileSystems` in `configuration.nix`.
- `nixos-anywhere`/kexec needs a writable root; **ZimaOS root is read-only**, hence the
  `./scripts/deploy kexec` step that streams a RAM installer (with static cpio/gzip since
  ZimaOS lacks them).
- **`kexec/run` jumps ~6s AFTER it returns**: nixos-images' `kexec-run.sh` ends with
  `nohup sh -c "sleep 6 && $SCRIPT_DIR/kexec -e" &`. So the staging dir must OUTLIVE the
  script — an `rm -rf` in an EXIT trap deletes the binary that performs the jump and the
  box silently stays on the old kernel. `kexec-local` clears its trap before jumping and
  then sleeps 60s on purpose. Covered by `checks.kexec-local`.
- **The kexec installer KEEPS the box's ssh host key**: `kexec-run.sh` copies
  `/etc/ssh/ssh_host_*` into the appended initrd and `restore-remote-access.nix` installs
  them back. So do NOT `ssh-keygen -R` after a kexec — the key does not change, and
  clearing it just throws away the known_hosts record.
- **`kexec-local` stages on `/var/tmp`, not `/tmp`**: `kexec-run.sh` appends a fresh cpio
  to `kexec/initrd` in place and execs binaries from that dir, so a size-capped or
  `noexec` tmpfs gives a half-written initrd or a bare "Permission denied".