# Arcline OS — architecture

This is the foundation ("the wires") for Arcline OS: a hardened, Debian-derived
operating system for people who run infrastructure. The landing page describes
the product; this repository is how it gets built.

## Design goals

1. **Secure by default** — hardened kernel, default-deny firewall, AppArmor,
   locked-down ssh. You opt *in* to exposure, never out.
2. **Zero telemetry** — no phone-home, no analytics, no cloud integration.
3. **btrfs-native** — snapshots and boot-to-snapshot rollback are built in.
4. **Production-ready from first boot** — observability pre-configured, tools
   pre-installed, everything documented.
5. **Auditable** — every script and config is plain text in this repo.

## How a build flows

```mermaid
flowchart LR
    A[editions/* metadata] --> B[debootstrap<br/>Debian bookworm]
    B --> C[install edition<br/>packages.list]
    C --> D[apply overlays<br/>base + edition]
    D --> E[configure-system.sh<br/>in chroot]
    E --> F[rootfs .tar.xz]
    F --> G[grub-mkrescue + squashfs<br/>→ live ISO]
    E -.toolchain .debs.-> C
```

Pipeline stages live in `scripts/`:

| Stage | Script | What it does |
|-------|--------|--------------|
| bootstrap | `build-rootfs.sh` | debootstrap minbase, apt sources, package install |
| overlay | `apply-overlays.sh` | copies `overlays/base` + `overlays/<edition>` into the rootfs |
| configure | `configure-system.sh` | runs *in the chroot*: hostname, locale, kernel cmdline, services, live-boot, toolchain |
| package | `build-iso.sh` | kernel + initramfs + squashfs → hybrid BIOS/UEFI ISO |
| orchestrate | `build-edition.sh` / `Makefile` | wire the above to `make iso-<edition>` |

## The four source trees

| Path | Role |
|------|------|
| `editions/` | per-edition **manifests**: package lists, kernel cmdline, fstab, metadata |
| `overlays/` | **files that land in the image**, organised as layered rootfs trees |
| `scripts/` | the **build pipeline** (all plain bash, readable top to bottom) |
| `btrfs/`, `toolchain/`, `observability/`, `tests/`, `ci/` | supporting subsystems |

There is no hidden magic: the Makefile is a thin wrapper, `versions.mk` /
`scripts/common.sh` hold the single source of truth for versions and paths.

## Zero telemetry, enforced

- No distro telemetry packages are installed (`ubuntu-report`,
  `popularity-contest`, snapd are never in a package list).
- apt automatic-update timers are **masked** in every edition's metadata.
- The firewall's output chain never initiates calls on its own.
- cloud-init is pointed only at the configured cloud datasource.
- The smoke tests (`tests/smoke/verify-rootfs.sh`) fail the build if telemetry
  artifacts are found.

## Follow-up work (explicitly out of scope for "the wires")

- Partitioning/installer that runs `btrfs/init.sh` on a target disk.
- Cloud images (qcow2/raw) for the `cloud` edition — the ISO path is wired,
  a disk-image path is the next step.
- Grafana/Loki packaged as `.deb`s rather than fetched from upstream.
- A signed (secure-boot) kernel for official releases.