bajia/README.md

# bajia

an init system (PID 1) for embedded / VM targets, written in C++20 and
configured with a small declarative language inspired by Android's init `.rc`
format.

## Status

- `.rc` config parser (services + on-trigger action blocks)
- Supervisor event loop built on `signalfd` + `epoll`
- service spawn / reap / respawn (per-service restart policy)
- action commands: `start`, `stop`, `restart`, `exec`, `mkdir`, `chmod`,
  `chown`, `setenv`, `write`, `symlink`, `mount`, `log`
- logger with a ring buffer that flushes to the console once available

roadmap:

- user/group privilege drop (`user`, `group`, supplementary groups)
- dependency ordering between services
- `SIGCHLD` crash-window limiting (rate-limited restarts)
- property triggers (`property:<k>=<v>`) and `setprop`/`getprop`
- per-service logging to files
- `reboot`/`poweroff` path with ordered unmount
- `SIGHUP` config reload
- SELinux

## building

requires a C++20 compiler and [Ninja](https://ninja-build.org/)

```sh
python3 configure.py     # generates build/build.ninja
ninja -C build           # produces build/bajia
```

`configure.py` also writes a thin `Makefile` convenience wrapper
(`make`, `make clean`, `make format`, `--asan`, `--debug`).

## running

As a real init, the kernel must launch it as PID 1:

```
init=/path/to/bajia
```

Or by hand against a config (useful for development, may not behave like a
real boot). bajia normally refuses to start unless it is PID 1; pass
`--run-as-user` to override:

```sh
./build/bajia --run-as-user etc/init.rc
```

If no files are given it looks for `/etc/bajia/init.rc`.

## configuration language

See [`etc/init.rc`](etc/init.rc) for a complete example.

### services

```rc
service NAME /path/to/exe [args...]
    user root|other          # privilege level (drop, planned)
    group GROUP [GROUP...]
    oneshot                  # run once and exit, never respawn
    disabled                 # not started by the boot sequence
    console                  # bind stdio to /dev/console
    class NAME               # grouping (default "default")
    respawn never|on-failure|always   # restart policy (default always)
    crash-threshold N        # restarts allowed per window
    crash-window SECS
    setenv K=V               # extra environment (repeatable)
    cwd /path
```

### actions

```rc
on TRIGGER
    start NAME | stop NAME | restart NAME
    exec /cmd args...
    mkdir PATH [mode]
    chmod PATH mode
    chown PATH uid gid
    setenv K V
    write PATH CONTENT
    symlink TARGET LINK
    mount SOURCE TARGET FSTYPE
    log message
```

boot triggers fire in order: `early-init`, `init`, `boot`. `shutdown` is
reserved (planned wiring to the signal path). property/`service-*` triggers
are on the roadmap.