depthcharge-tools 0.6.2

Tools to manage the Chrome OS bootloader

This project is a collection of tools that ease and automate interacting with depthcharge, the Chrome OS bootloader.

Depthcharge is built into the firmware of Chrome OS boards, uses a custom verified boot flow and usually cannot boot other operating systems as is. This means someone who wants to use e.g. Debian on these boards need to either replace the firmware or work their system into the format depthcharge expects. These tools are about the latter.

Right now these are developed on and tested with only a few boards, but everything will attempt to work on other boards based on my best guesses.

mkdepthcharge

The mkdepthcharge tool is intended to wrap mkimage and vbutil_kernel to provide reasonable defaults to them, hide their idiosyncrasies and automate creating a depthcharge-bootable partition image appropriate for the running architecture. An example invocation on a Samsung Chromebook Plus (v1, arm64) could be:

$ mkdepthcharge -o depthcharge.img --compress lzma \
    --cmdline "console=tty1 root=/dev/mmcblk0p2 rootwait" -- \
    /boot/vmlinuz.gz /boot/initrd.img rk3399-gru-kevin.dtb

Here, mkdepthcharge would automatically extract and recompress the kernel, create a FIT image, put command line parameters into a file, create an empty bootloader, and provide defaults for vboot keys and other arguments while building the partition image.

depthchargectl

The depthchargectl tool goes a step further and aims to fully automate bootable image creation and Chrome OS kernel partition management, even the board-specific and distro-specific parts. With proper integration with your distribution, depthchargectl can keep your system bootable across kernel and initramfs changes without any interaction on your part. Even without such integration, a single command automates most of the work:

# Use --allow-current if you only have one Chrome OS kernel partition.
$ sudo depthchargectl write --allow-current
Building depthcharge image for board 'Samsung Chromebook Plus' ('kevin').
Built depthcharge image for kernel version '5.10.0-6-arm64'.
Wrote image '/boot/depthcharge/5.10.0-6-arm64.img' to partition '/dev/mmcblk1p1'.
Set partition '/dev/mmcblk1p1' as next to boot.

# After a reboot, you or an init service should run this.
$ sudo depthchargectl bless
Set partition '/dev/mmcblk1p1' as successfully booted.

Installation

This depends on the pkg_resources Python package which is usually distributed with setuptools. The tools can run a number of programs when necessary, which should be considered dependencies:

• futility (vbutil_kernel), cgpt, crossystem

• mkimage, fdtget, fdtput

• lz4, lzma

• gzip, lzop, bzip2, xz, zstd (optional, for unpacking compressed /boot/vmlinuz)

The rst2man program (from docutils) should be used to convert the mkdepthcharge.rst and depthchargectl.rst files to manual pages. However, this is not automated here and has to be done manually.

This project (or at least depthchargectl) is meant to be integrated into your operating system by its maintainers, and the best way to install it is through your OS’ package manager whenever possible.

Debian

An official depthcharge-tools Debian package is available upstream, since Debian 12 (bookworm). You can install it like any other package:

$ sudo apt install depthcharge-tools

It includes the necessary system hooks and services to make and keep your Chromebook bootable, enabled by default. These however do not trigger on the depthcharge-tools installation, but on kernel and initramfs changes. To trigger these hooks manually, run:

$ sudo update-initramfs -u

Alpine Linux

Thanks to the efforts in supporting postmarketOS on ChromeOS Devices, there is an official depthcharge-tools package for Alpine Linux. You should be able to install it as:

$ sudo apk add depthcharge-tools

However, this doesn’t include any system hooks or services to keep your Chromebook bootable.

Pip

Python binary wheels are uploaded to PyPI, and it should be possible to install the python package using pip. However, this does not install the manual pages, bash/zsh completions, systemd/init.d service files, and OS-specific kernel/initramfs hooks.

You can install in –user mode, but this makes it quite hard to use depthchargectl as root. As root privileges are necessary to manipulate system block devices this limits you a bit:

$ pip install --user depthcharge-tools

Although inadvisable, you can install as root to overcome that caveat. Alternatively, see the PYTHONPATH hack in one of the later sections.

Configuration

You can configure depthcharge-tools with the /etc/depthcharge-tools/config file, or by putting similar fragments in the /etc/depthcharge-tools/config.d directory. See the config.ini file for the built-in default configuration.

Settings in the [depthcharge-tools] section are the global defaults from which all commands inherit. Other than that, config sections have inheritence based on their names i.e. those in the form of [a/b/c] inherit from [a/b] which also inherits from [a]. Each subcommand reads its config from such a subsection.

Currently the following configuration options are available:

[depthcharge-tools]
enable-system-hooks: Write/remove images on kernel/initramfs changes
vboot-keyblock: The kernel keyblock file for verifying and signing images
vboot-private-key: The private key (.vbprivk) for signing images
vboot-public-key: The public key for (.vbpubk) verifying images

[depthchargectl]
board: Codename of a board to build and check images for
ignore-initramfs: Do not include an initramfs in the image
images-dir: Directory to store built images
kernel-cmdline: Kernel commandline parameters to use
zimage-initramfs-hack = How to support initramfs on x86 boards

For longer explanations check the manual pages of each command for options named the same as these.

Installation for development

If you want to use development versions, you can clone this repository and install using pip:

$ pip3 install --user -e /path/to/depthcharge-tools

Hopefully, you should be able to use depthchargectl with just that:

$ depthchargectl build --output depthcharge.img
Building depthcharge image for board 'Samsung Chromebook Plus' ('kevin').
Built depthcharge image for kernel version '5.10.0-6-arm64'.
depthchargectl.img

Most depthchargectl functionality needs root as it handles disks and partitions, and you need special care while invoking as root:

$ depthchargectl() {
    sudo PYTHONPATH=/path/to/depthcharge-tools \
        python3 -m depthcharge_tools.depthchargectl "$@"
}

$ depthchargectl list /dev/mmcblk0
S  P  T  PATH
1  2  0  /dev/mmcblk0p2
1  1  0  /dev/mmcblk0p4
0  0  15 /dev/mmcblk0p6

Or you can add a similar invocation to the /usr/local/bin files, so that it’s available to both normal users and root:

$ sudo tee /usr/local/bin/depthchargectl <<EOF
#!/bin/sh
export PYTHONDONTWRITEBYTECODE=1
export PYTHONPATH=/path/to/depthcharge-tools
exec python3 -m depthcharge_tools.depthchargectl "\$@"
EOF

$ sudo chmod +x /usr/local/bin/depthchargectl

License

Copyright (C) 2019-2023 Alper Nebi Yasak <[e-mail]>

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>

See COPYRIGHT and LICENSE files for full copyright information.