Install (or rescue) Alpine Linux on a headless system

Alpine Linux documentation assumes initial setup is carried-out on a system with a keyboard & display to interract with.
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).

This repo provides an overlay file to initially bootstrap¹ a headless system (leveraging Alpine distro's initramfs feature): it starts a basic 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.

Install procedure:

Please follow Alpine Linux Wiki to download & create installation media for the target platform.
Tools provided here can be used on any plaform for any install modes (diskless, data disk, system disk).

Just add headless.apkovl.tar.gz² overlay file at the root of Alpine Linux boot media (or onto any custom side-media) and boot-up the system.
With default network interface definitions (and SSID/pass file if using wifi), system can then be remotely accessed with: ssh root@<IP>
(system IP address may be determined with any IP scanning tools such as nmap).

As with Alpine Linux initial bring-up, root account has no password initially (change that during setup!).
From there, actual system install can be performed as usual with setup-alpine for instance (check wiki for details).

Extra files may be added next to headless.apkovl.tar.gz to customise boostrapping configuration (check sample files):

• wpa_supplicant.conf³ (mandatory for wifi usecase): define wifi SSID & password.
• interfaces³ (optional): define network interfaces at will, if defaults DCHP-based are not suitable.
• ssh_host_*_key* (optional): provide custom ssh keys to be injected (may be stored), instead of using bundled ones² (not stored). Providing an empty key file will trigger new keys generation (ssh server may take longer to start).
• unattended.sh³ (optional): create custom automated deployment script to further tune & extend actual setup (backgrounded).

Goody: seamless USB-ethernet gadget boostrapping (PiZero for instance):
On supporting Pi devices, just add dtoverlay=dwc2 in usercfg.txt (or config.txt), and plug USB cable into Computer port.
With Computer set-up to share networking with USB interface as 10.42.0.1 gateway, one can log into device from Computer with: ssh root@10.42.0.2

Main execution steps are logged in /var/log/messages.

How to customize ?

This repository may be forked/cloned/downloaded.
Main script file is headless.start.
Execute ./make.sh to rebuild headless.apkovl.tar.gz after changes.

Credits

Thanks for the initial guides & scripts from @sodface and @davidmytton.

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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. ↩︎

2. About bundled ssh keys: as this package is essentially intended to quickly bootstrap system in order to configure it, it purposely embeds some ssh keys so that bootstrapping is as fast as possible. Those (temporary) keys are moved in RAM /tmp, so they will not be saved/reused once permanent configuration is set (with or without ssh server voluntarily installed in permanent setup). ↩︎

3. These files are linux text files: Windows/macOS users need to use text editors supporting linux text line-ending (such as notepad++, BBEdit or any similar). ↩︎