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 one arm64 board, but everything will attempt to work on other boards based on my best guesses. Support for x86 boards is very limited at a fundamental level due to a lack of understanding on my part.
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.
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.
These tools depend on mkimage, vbutil_kernel, cgpt, and
other utilities (util-linux, coreutils, etc.) that are usually
installed by default on most Linux systems, so you need to install those
first. You also need docutils to build the manual pages with
rst2man, but only for that.
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.
An unofficial Debian package is available in the releases page, with it's packaging source tracked in salsa. After downloading, you can install with:
$ sudo apt install ./depthcharge-tools_*.deb
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.
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
For longer explanations check the manual pages of each command for options named the same as these.
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
I only own one chromebook, so I need your help to make it work with all others. Pull requests, bug reports, or even pointers in the right direction for existing issues are all welcome. Currently I need the most help with x86 boards.
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/>