I've read the guides for updating/installing a downloaded Maemo firmware:
http://maemo.nokia.com/n900/tips/software-update/
http://wiki.maemo.org/Updating_the_tablet_firmware

but after searching a lot, I haven't found the way to make a backup of the firmware with all the data.
Of course I need a procedure to make it with a Linux PC.

If you mean a bit copy, then you can't, buy you don't need it, as only a few things get stored on the root and those are backed up.

You could try a SSH connection and use transport over to get files, but there's little point as the same files are inside the firmware flash image.

You can't back up the installed apps data, but you can backup the list of apps installed on your device. There is no way to do a full backup and recovery on this device to be honest. Just partial entries of what can be backup.

- No way to backup the filesystem (as Partimage does)?

- Plugging the device to a Computer USB port, can be all the filesystems mounted?

- If I backup the directory tree with the files (via SFTP), can I restore them later?

A Partition backup is possible, but its not designed for easy use. Isnt even an application, but a technique

Here is a how-could (like a how-to, but YMMV): http://metalab.at/wiki/Hack-A-N900/D...e_rootfs_Image

In the end, you will do backup with dd if=/dev/mtd5 | ssh root@yourlinuxpc "cat > rootfs.img"
and a restore with the flasher ./flasher-3.5 -r rootfs.img -f -R

But keep in mind that you are playing with bare data, so you must know what are you doing if something goes wrong

You have a much higher risk of something going wrong if you do it like that than using the stuff designed to back up the partition.

Why would you want to back up the root partition anyway? 99% of what's in there is in the flash image. The little there is left is probably configuration files you can just copy to the home partition in a backup structure.

I've found that YMMV = Your results may vary.

Well, I see that is needed to modify the firmware to backup it, but is a solution.

I hope that a next version of Flasher will be released with backup support (bi-directional functions).

ndi, what is "the stuff designed to back up the partition"? Is something better?

The reason of the full backup is to have option to restore the device exactly in the same state as the vendor released to me. Not with a new or developer version: with the originally provided by the vendor, without any different file.
This can make easier to make use of warranty and support.

If you mean at PR 1.0, you can't. Flashing up upgrades the internal flash of the radio modem, as a result reverting to any previous version (1.0 versus 1.1 versus 1.2) will render the GSM unworkable. The only way to keep 1.0 is to never upgrade, ever.

If you mean "clean" firmware, reflashing both the root and the EMMC restores exactly to clean, as it's what the darn thing does. (minus the lock code)

If you flash it to PR 1.2 (with MMC) over the old, modified PR 1.2 there's no telltale, you can replace your kernel in peace. However, should you fry your device with OS, it won't start and there's no reflashing a brick. Plus, heat damage to a CPU is recognizable, that's why it's not banned and companies still accept returns for components that still have water coolers on.

Plus, it's not illegal to modify your OS unless you use it to get out of a contract. It's your phone and you're free to do whatever you want with it. Should you fry with OC, they'll probable able to tell, regardless. Not that having a different kernel means you OCd it.

I posted a thread a while back with a script to backup /opt and /home/user to MyDocs as tar files. That should get you almost everything. Just copy the resulting files off onto your pc.

Yous should be able to copy files back to a freshly flashed device as desired (pay attention to permissions though).

One note, it check to make sure the device is charging before backing up.