Sunday, January 23, 2011

Running your own code on the Kobo

This article is part of an extended series on Kobo development and investigation

Apparently I have to make this more obvious:

  • Take a backup of your Kobo's SD card before doing anything. If something doesn't work, you can't fix your Kobo without this backup. I will not send you a backup.
  • Any device hacking is risky. If you can't afford to break your device, leave now.

The 1.7.4 update tarball (see contains a new copy of /etc/init.d/rcS. Reading it tells us how to replace files on the Kobo's root file system, giving us a way to replace rcS with a patched version that calls out to a shell script on the more easily writable FAT32 main flash, so we can tinker with the system with minimal risk. This initial change is risky, though, as you might render your Kobo useless with a typo!

Replacing files on the Kobo Wifi's root file system

The Kobo Wifi's /etc/init.d/rcS startup script tests for the presence of a number of files within the .kobo subdirectory of the main fat32 partition.

Two notable files are .kobo/Kobo.tgz and .kobo/KoboRoot.tgz. If these files exist, they will be extracted into /usr/local/kobo or / (the root directory) respectively. The system uses this mechanism to apply incremental updates.

We can exploit this mechanism to insert our own files onto the device's main memory or very carefully replace existing files. If you screw it up you might render your Kobo useless and possibly irreparable, so don't try anything unless you don't mind breaking it.

You're much better off copying the firmware from the internal microSD card to a 2G SD card then booting off the external SD by holding "enter" down during power-on. Getting the image for this requires physically opening the Kobo to get to it, unless someone finds an image of it hosted by Kobo somewhere, though.

BTW, the rcS script also looks for .kobo/upgrade and if found, runs /etc/init.d/ . This is probably the hook for a full upgrade installation. Don't mess with it.

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