The Nokia N900 is able to upgrade its operating system over the air, which is the best way to upgrade it, especially if you have a fast Internet connection. This is also very practical when you're not running Windows because the Nokia suite only exists on that platform. This is exactly what I had been doing since I bought my N900. Except that a few months ago, I declined to update when requested for a reason I have now forgotten, probably because I didn't have the time then. And since then, it has failed to propose any new upgrade. So the only solution was to flash it but I had no idea how to do that on Linux. Luckily, I found a very handy guide on the subject which includes a version for Linux. Unfortunately, this guide is light on details and not fully correct so here's the fix.
Note that flashing the device rather than upgrading it over the air will remove all software you previously installed, as well as some of your settings. It will not delete your data as it only flashes the root partition. Your address book for instance is safe. But I would still strongly advise that you backup your device before going any further. The N900 ships with a backup utility so please use it and copy the backup file to your computer. If you fail to do so and you lose all your data, you're on your own to recover it.
Flashing the Device
As the guide explains, download the Linux Flasher Tool and the latest available N900 firmware image. You will need to enter your device ID for the image and in both cases you will need to accept Nokia's license agreement.
If you are using Ubuntu, I suggest you download the
.deb version of the flasher tool:
maemo_flasher-3.5_188.8.131.52_i386.deb, then double-click on the downloaded file and the package installer will open. Install the package. The flasher tool will then be installed to
/usr/bin, not in the current directory, as suggested by the article.
For the image, ignore all the red warnings on the page next to the eMCC image links and download the latest combined image for your region, in my case
Go through steps 3 and 4 as explained in the guide: turn the phone off and connect it to your computer via the USB cable.
Now comes the glitch in the guide: the actual command to flash the image needs to specify where to find the image in question:
$ sudo flasher-3.5 -F /path/to/image.bin -f -R
When you run the tool, you will get quite a bit of output when it validates the image. It will eventually show the following message:
Suitable USB device not found, waiting.
And the tool will hang. This message is not an error message as the guide says, even though it sounds a bit ominous, it's the flasher tool's way to tell you that you need to switch the device on so that it can find it. So switch the phone on. As soon as you do so, the flasher tool will recognise it and will start loading the image. It will provide on-screen feedback while it does so and the N900 will display a small progress bar at the bottom of the Nokia boot image. Once the tool has finished, the phone will take a lot longer than usual to start up. Don't try to hurry things along, just wait until it is fully booted. Then, and only then, disconnect the phone from the computer.
As mentioned above, you then need to re-install the software you had previously installed on the device. Luckily the OVI application store remembers what you previously paid for and downloaded so you should be able to just re-download software without having to pay for it again.