kos: a minimal operating system that runs KOReader

[ratiz]

kos is an open-source operating system that can replace the stock OS. It comes with KOReader as the graphical user interface.

Currently it only supports the Clara Colour, but if someone is interested I could easily add support for the Libra Colour and the Clara BW.

Compared to the stock OS, kos doesn't come with any additional features, except that it is certainly smaller. As you might know, the most recent Kobo models have a secure boot chain that makes it much harder to boot a different kernel. My intent with kos is to provide a simple, open-source OS that can serve as an example for further Kobo hacking. I hope that having more control over one's hardware will help make even better open-source software possible.

Because this installation will write to partitions essential for the boot process, it is much riskier than the installations you might usually find on this forum. If the installation goes wrong, it will likely brick your device. So far, it has only been tested on my kobo with firmware version 4.39.22468 and 4.46.23836 but I would expect it to work on all 4.x firmware versions.

Install:

Before the installation make sure that you have a Kobo Clara Colour and that it runs on firmware 4.x. Backup all your data as it will be erased during the installation.

For the installation, use the provided KoboRoot.tgz at the end of the post at your own risks. I am not responsibe if it bricks your device.

After the installation, to display your local time, set the time zone with:

# ln -sf /usr/share/zoneinfo/Area/Location /etc/localtime

To access a shell, you can use, for example, the terminal emulator provided by KOReader or its built-in SSH server.

Uninstall:

Run the command below and you will be back to the stock OS after reboot.

# ntx_hwconfig -S 1 -p /dev/mmcblk0p6 BootPartNo 0xB

Credits:

• tux-linux for creating Quill OS and helping me to learn how to make an operating system for a kobo device

Source Code | KoboRoot.tgz

[geek1011]

I have a trick I made a few years ago you can use to safely try alternative root filesystems by doing a fake-A/B-ish kinda thing.

I'll see if I can polish it up and share it.

[ratiz]

Originally Posted by geek1011

I have a trick I made a few years ago you can use to safely try alternative root filesystems by doing a fake-A/B-ish kinda thing.

That would interesting to see. Do you use a loop device? I don't see otherwise how you can do that without touching the partitions.

[ratiz]

I have updated the KoboRoot.tgz to install kos.

Here is a list of the changes made:

• Use the KOReader kobov5 release, which is optimized for the latest ereaders (compilation flags targeting the cores of the MediaTek SoCs).
• Installation should be a bit safer. kos installer will now remove itself if it fails to patch Little Kernel or if it detects that the device is not a Clara Colour. Also, even if someone tries to install kos on firmware 5 it shouldn't do anything since firmware 5 doesn't use KoboRoot.tgz.
• The integrity of u-boot and linux FIT images is now checked
• wpa_supplicant is now compiled with WPA3 support and wpa_cli binary was added.

[geek1011]

Originally Posted by ratiz

That would interesting to see. Do you use a loop device? I don't see otherwise how you can do that without touching the partitions.

Yeah, I do a loop device, but the real trickery is that I have an additional init binary at /init (which takes priority) which mounts them, handles a/b switching, patches the loaded kernel via /dev/kmem (rather than a kernel module so it's universal) to swap the device major/minor for the sdcard partitions to the loop one (replacing an unused syscall with kmalloc to do the memory allocation for the hook trampoline from userspace), patches some scripts which care about it (there's only about 3, and it's relatively minor) by bind-mounting over it, then execs the real init. This allows everything else to work unmodified, including Kobo's USB mass storage mode. I originally wrote this for testing multiple firmware versions in parallel while working on patches. I didn't publish it since there are a few pitfalls, and new versions need to be audited (since if they started using udev netlink, this doesn't handle it).

I don't have time to polish it for the next 3 weeks, but you can probably get 90% of the way there having a LLM remake it from my description.

[ratiz]

It is much more involved than I expected. I find this impressive.

Why did you choose that approach rather than compiling a modified kernel that would do what you want? The latter seems easier to me and also safe because you can always write back the original kernel on the SD card (assuming it is a SD card and not eMMC).

The newer kobos don't have the /dev/kmem device.

[root@kobo ~]# gunzip -c /proc/config.gz | grep CONFIG_DEVKMEM
# CONFIG_DEVKMEM is not set

[rantanplan]

Didn’t they replace the sdcard with emmc on the current devices?

[PatchyMimo]

Originally Posted by rantanplan

Didn’t they replace the sdcard with emmc on the current devices?

AFAIK yes. At least as far as Libre Colour goes, I don't have a Clara Colour but I'm sure someone who does would know.

[DNSB]

The Kobo models in the list below do not have removable internal storage. The original Aura N514 can use it's external µSD to rewrite the internal storage. The others required ADB, fastbook and software to recover. IMNSHO, this makes them bad candidates for most modifications since recovering from errors is difficult.

Kobo N905 Touch
Kobo N709 Aura One
Kobo N867 Aura H2O Edition 2
Kobo N782 Forma
Kobo N777 & N778K Sage
Kobo N365 Clara BW
Kobo N367 Clara Colour
Kobo N428 Libra Colour