114 lines
4.1 KiB
Markdown
114 lines
4.1 KiB
Markdown
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# mdns-termux
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**mDNS + Tailscale hostname resolution for Termux (Android).**
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Termux runs on Android's Bionic libc, which does **not** resolve `.local` names
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and lacks `getent`. This repo ships small, dependency-light helpers that fix
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that — without root, and without a custom system resolver.
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Works on any network: LAN via multicast, off-LAN via Tailscale MagicDNS.
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---
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## What's in here
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| Script | Role |
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|--------|------|
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| `mdns-resolve` | Resolve `<host>.local` via raw multicast UDP (pure Python, stdlib only). |
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| `mdns-publish.py` | Publish this device on the LAN as `movil.local` using `zeroconf`. |
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| `ssh-mdns-proxy` | SSH `ProxyCommand`: mDNS → Tailscale DNS → cached IP. |
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| `ssh-fallback` | SSH `ProxyCommand`: Tailscale → LAN, for flaky Tailscale. |
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| `resolve` | Generic resolver for **any** command (ping, curl, kubectl, nc…). Same order. |
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## Install
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```bash
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git clone https://devops.ingeniumcodex.com/andresgarcia0313/mdns-termux.git
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cd mdns-termux
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bash install.sh # or --dry-run first
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```
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Then follow the printed reminders (append `bashrc.snippet`, set your
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`TAILSCALE_DOMAIN`, optionally merge `ssh_config.example`).
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## Usage
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### Generic resolver — works in any command
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```bash
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resolve lenovo # -> 100.69.236.16
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ping $(resolve hp62a)
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curl "http://$(resolve dell):8080"
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kubectl --server="https://$(resolve master):6443" get nodes
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```
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Environment knobs:
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- `TAILSCALE_DOMAIN` — defaults to `tailb0bb74.ts.net`. Set to your own tailnet.
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- `MDNS_TIMEOUT` — seconds waiting for multicast (default `1`, keeps off-LAN snappy).
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### Shell helpers (from `config/bashrc.snippet`)
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```bash
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alias r='resolve'
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pingr <host> # ping -c 3 to resolved IP
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curlr <host> [flags] # curl http://<resolved-ip>
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sshr <host> [cmd...] # ssh via resolved IP with correct HostKeyAlias
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```
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### SSH by hostname (via `ProxyCommand`)
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Drop `config/ssh_config.example` into `~/.ssh/config`. Then:
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```bash
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ssh lenovo # resolves via mDNS then Tailscale, connects
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ssh lenovo.local # forces mDNS-first path
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```
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### Publishing this device as `movil.local`
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```bash
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python ~/.local/bin/mdns-publish.py # foreground
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nohup python ~/.local/bin/mdns-publish.py >>~/.cache/mdns.log 2>&1 & disown
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```
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## Behavior by network
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| Scenario | Path | Typical latency |
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|--------------------|--------------------------------------------|-----------------|
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| On home LAN | mDNS multicast (1 s cap) → else Tailscale | < 100 ms |
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| Mobile data / away | mDNS fails → Tailscale MagicDNS | < 200 ms |
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| No Tailscale | Both fail → cached last-known IP | instant |
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## Gotchas found the hard way
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- **`getent` doesn't exist on Termux.** Scripts that shell out to it silently
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fail. This repo uses `python -c "import socket; socket.gethostbyname(...)"`
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as the portable fallback on Bionic.
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- **Shebang matters.** `#!/data/data/com.termux/files/usr/bin/bash` is required
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for `declare -A`. A stray backslash (`#\!`) makes the kernel fall through to
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`sh`, which rejects bash-only syntax with `Syntax error: "(" unexpected`.
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- **mDNS off-LAN is a no-op.** Multicast (224.0.0.251) does not cross networks.
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Over mobile data, only Tailscale resolves.
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- **`zeroconf` is not `pkg`-managed.** After restoring Termux from a `tar`
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backup, re-run `pip install zeroconf` or `mdns-publish.py` will silently die
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with `ModuleNotFoundError`.
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- **Silent failures are the enemy.** The `.bashrc` snippet deliberately logs
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to `~/.cache/mdns.log` instead of `/dev/null`. Keep it that way.
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## Tailscale on Termux
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Tailscale runs as the **Android app**, not as a Termux CLI — `tailscale up`
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inside a shell won't work. The app provides MagicDNS for
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`*.<your-tailnet>.ts.net`, which Bionic-libc resolves fine (it's just a
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regular DNS lookup).
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## Related
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- [claude-code-termux](https://devops.ingeniumcodex.com/andresgarcia0313/claude-code-termux)
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— Claude Code CLI setup for Termux. Uses this repo for SSH/host resolution.
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## License
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MIT — see `LICENSE`.
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