Rescue USI

Build a minimal and opinionated rescue USI (unified kernel image with embedded root filesystem), i.e. a single EFI executable containing a minimal yet complete system for recovery.

Why?

You tinker, things break. They say every Arch Linux user carries a USB stick with the installation disk around, just in case.

With this image, you don't need to. Put the image on your ESP, and boot it rescue your Linux installation.

How?

Make sure you have recent versions of mkosi and systemd-ukify installed.

First, set a root password:

$ printf "hashed:%s\n" "$(openssl passwd -6)" > mkosi.rootpw
$ chmod 600 mkosi.rootpw

Note: Without this step you cannot log in on the rescue image, so don't forget it. Alternatively,

• write hashed: to mkosi.rootpw to make root have an empty password, or
• pass --autologin when building the image (see below) to have root automatically login on the first console (at your own risk!).

Then, build the image:

$ mkosi build

Note: If you did not set up user namespaces, you have to run the above command as root.

Then, put the image on your EFI partition (or on the XBOOTLDR partition if your EFI system partition is too small):

# install -m644 -t /efi/EFI/Linux mkosi.output/*.efi

If you place it in EFI/Linux systemd-boot will discover it automatically without further configuration.

Image version

By default, mkosi reads the version of this image from the mkosi.version file; together with the distribution release version this helps you identify what rescue image you have.

However, for a rolling release distribution which has no distribution release version, i.e. Archlinux specifically, you can chose an explicit image version to help identify the image contents:

$ mkosi build --image-version="$(git rev-parse --short=10 HEAD)-(date --utc +%Y%m%d%H%M)"

Secure boot

After installing the rescue image to /efi you can sign it for secure boot, e.g. with sbctl sign.

mkosi can also sign the image by itself, using sbsigntools. For this you need to set SecureBootKey= and SecureBootCertificate=, e.g in mkosi.local.conf.

Customization

By default, the image builds for the same distribution as the host, i.e. if you're running an Arch system it build an Arch image. You can customize this by setting the Distribution key in mkosi.local.conf.

You can put additional options for mkosi into mkosi.local.conf which is ignored by git. You can also fork the repository and freely adapt the configuration to your own needs.

Refer to mkosi(1) for more information.

License

This code in this repository is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

Packages inside the generated rescue image are covered by their respective licenses.