# 03 — SSH, mDNS and Tailscale on Termux

Termux's Bionic libc does **not** resolve `.local` names. This repo ships small Python helpers that fix this without needing root or a custom resolver.

## Scripts involved

| Script | Role |
|--------|------|
| `mdns-resolve` | Resolve `<host>.local` via raw multicast UDP. Returns the IP or non-zero. |
| `mdns-publish.py` | Publish this device on the LAN as `movil.local` (or whatever you choose) using `zeroconf`. |
| `ssh-mdns-proxy` | SSH `ProxyCommand` that tries mDNS first, then Tailscale DNS. Used from `~/.ssh/config`. |
| `ssh-fallback` | Lower-level fallback: tries Tailscale, then LAN. Useful when Tailscale is flaky. |

## SSH config

Drop the contents of `config/ssh_config.example` into `~/.ssh/config` (or merge it).

The key entries:

```ssh-config
Host *.local
    ProxyCommand ~/.local/bin/ssh-mdns-proxy %h %p

Host lenovo-ideapad
    ProxyCommand ~/.local/bin/ssh-mdns-proxy %h %p

Host *.YOUR-TAILNET.ts.net
    User YOUR_USER
```

Adjust the username and the tailnet domain. The proxy command will try mDNS first, then fall through to your Tailscale magic-DNS name (env `TAILSCALE_DOMAIN`).

## Publishing this device as `movil.local`

If you want the device to be reachable as `movil.local` from your LAN:

```bash
# One-shot foreground (to see errors):
python ~/.local/bin/mdns-publish.py

# Background (typical use, from ~/.bashrc):
nohup python ~/.local/bin/mdns-publish.py >>~/.cache/mdns.log 2>&1 &
disown
```

**Gotcha:** `zeroconf` (the pip package) is **not** part of a `pkg`-managed install. If you restore Termux from a `tar` backup, `zeroconf` will be missing from `$PREFIX/lib/python*/site-packages` and the script will silently fail with `ModuleNotFoundError`. Re-run `pip install zeroconf` after every restore.

## Logging, not silencing

The `.bashrc` auto-start lines in this repo (`config/bashrc.snippet`) deliberately log to a file instead of `/dev/null`. Silent failures are the single most painful class of bug after a restore — keep the logs.

## Tailscale

Tailscale on Termux runs **as the Android app**, not as a CLI inside Termux. You can't `tailscale up` from a shell. The app provides magic DNS for `*.YOUR-TAILNET.ts.net`, which Bionic-libc resolves fine (it's just a regular DNS query).

When you list hosts in `~/.ssh/config`, prefer:
1. `<host>.local` for fast LAN access
2. `<host>.YOUR-TAILNET.ts.net` for off-LAN

Never hardcode IPs — they rotate.