54 lines
4.5 KiB
Markdown
54 lines
4.5 KiB
Markdown
# Bootstrap Alpine Linux on a headless system
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[Alpine Linux documentation](https://docs.alpinelinux.org/user-handbook/0.1a/Installing/setup_alpine.html) assumes **initial setup** is carried-out on a system with a keyboard & display to interract with.\
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However, in many cases one might want to deploy a headless system that is only available through a network connection (ethernet, wifi or as USB ethernet gadget).
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This repo provides an **overlay file** to initially bootstrap[^1] a headless system (leveraging Alpine distro's `initramfs` feature): it starts a ssh server to log-into from another Computer, so that actual install on fresh system (or rescue on existing disk-based system) can then be performed remotely.\
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An optional script may also be launched during that same initial bootstrap, to perform fully automated setup.
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## Setup procedure:
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Please follow [Alpine Linux Wiki](https://wiki.alpinelinux.org/wiki/Installation#Installation_Overview) to download & create installation media for the target platform.\
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Tools provided here can be used on any plaform for any install modes (diskless, data disk, system disk).
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Just add [**headless.apkovl.tar.gz**](https://is.gd/apkovl_master)[^2] overlay file *as-is* at the root of Alpine Linux boot media (or onto any custom side-media) and boot-up the system.\
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With default DCHP-based network interface definitions (and [SSID/pass](#extra-configuration) file if using wifi), system can then be remotely accessed with: `ssh root@<IP>`\
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(system IP address may be determined with any IP scanning tools such as `nmap`).
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As with Alpine Linux initial bring-up, `root` account has no password initially (change that during target setup!).\
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From there, actual system install can be performed as usual with `setup-alpine` for instance (check [wiki](https://wiki.alpinelinux.org/wiki/Alpine_setup_scripts#setup-alpine) for details).
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## Extra configuration:
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Extra files may be added next to `headless.apkovl.tar.gz` to customise boostrapping configuration (check sample files):
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- `wpa_supplicant.conf`[^3] (*mandatory for wifi usecase*): define wifi SSID & password.
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- `unattended.sh`[^3] (*optional*): provide a deployment script to automate setup & customizations during initial bootstrap.
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- `interfaces`[^3] (*optional*): define network interfaces at will, if defaults DCHP-based are not suitable.
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- `authorized_keys` (*optional*): provide client's public SSH key to secure `root` ssh login.
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- `ssh_host_*_key*` (*optional*): provide server's custom ssh keys to be injected (may be stored), instead of using bundled ones[^2] (not stored). Providing an empty key file will trigger new keys generation (ssh server may take longer to start).
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**Goody:** seamless USB-serial & USB-ethernet gadget mode (PiZero for instance):\
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On supporting Pi devices, just add `dtoverlay=dwc2,dr_mode=peripheral` in `usercfg.txt` (or `config.txt`), and plug USB cable into host Computer port.\
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Serial terminal can then be connected-to from host Computer (e.g. `cu -l ttyACM0` on Linux. xon/xoff flow control).\
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Alternatively, with host Computer set-up to share networking with USB interface as 10.42.0.1 gateway, one can log into device from host with: `ssh root@10.42.0.2`.
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Main execution steps are logged: `cat /var/log/messages | grep headless`.
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[^1]: Initial boot fully preserves system's original state (config files & installed packages): a fresh system will therefore come-up as unconfigured.
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[^2]: About bundled ssh keys: this overlay is meant to **quickly bootstrap** system in order to then proceed with proper install; therefore it purposely embeds [some ssh keys](https://github.com/macmpi/alpine-linux-headless-bootstrap/tree/main/overlay/tmp/.trash) so that bootstrapping is as fast as possible. Those temporary keys are moved in RAM /tmp: they will **not be stored/reused** once actual system install is performed (whether or not ssh server is installed in final setup).
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[^3]: These files are linux text files: Windows/macOS users need to use text editors supporting linux text line-ending (such as [notepad++](https://notepad-plus-plus.org/), BBEdit or any similar).
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## Want to tweak more ?
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This repository may be forked/cloned/downloaded.\
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Main script file is [`headless.start`](https://github.com/macmpi/alpine-linux-headless-bootstrap/tree/main/overlay/usr/local/bin/headless_bootstrap).\
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Execute `./make.sh` to rebuild `headless.apkovl.tar.gz` after changes.\
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(requires `busybox`; check `busybox` build options if not running from Alpine or Ubuntu)
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## Credits
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Thanks for the initial guides & scripts from @sodface and @davidmytton.
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