DISCLAIMER: I did not invent these steps. I merely followed the instructions at the official Wiki guide of Maemo 5 located here:
http://wiki.maemo.org/Updating_the_firmware. However, there are no pictures or illustrations in this wiki so I think there will be new users who may get confused, especially if they are new to Linux. So I decided to post the instructions that I followed but this time it has screenshots to help you better.
PREPARATION:
UPDATE April 8, 2012: Download the following from
here.
1. Flasher Application. Read the description to know which one to download, i.e. Windows-based or Linux-based.
2. FIASCO Image. This is the Image file to flash the RootFS (or the Operating System) of the N900.
3. eMMC Image. There are 2 types of eMMC Images in the download link: Original and 8GB. Download the Original if you want to flash your N900 with stock setup, or download the 8GB if you plan to install NITDroid.
4. Flashing Instructions 2012. This is a notepad file that contains the steps.
Install the Flasher by opening Terminal (it's like the Command Prompt in Microsoft Windows) and typing the following, or copy-paste it. You will replace <flasher-package-name> with the actual file name of the Flasher application.
For Debian-based Linux OS (like Ubuntu) where you downloaded the .deb file:
If you're using a 64-bit system for Linux, type this:
For non Debian-based Linux OS (like Fedora)where you downloaded the .tar.gz file, extract the contents of the .tar.gz file into your desired folder/directory.
For Windows: the installer is in the form of an .exe file. Just run the file by double-clicking or right-click with the mouse and choose "Open".
Make sure that your N900 is fully charged.
Make sure that you are using a 32-bit Operating System.
NEXT: Actual steps for flashing the Nokia N900
SUMMARY OF NEXT STEPS TO BE DISCUSSED:
Step 1: Flash the Operating System (rootfs) first
Step 2: Flash the eMMC (the 32GB internal storage)
Step 3: Flash the Operating System again (VERY IMPORTANT)