to initialize/clone a new-to-you n900 from a failing N900 and race toward a backupmenu restore
if you can do a backupmenu backup archive, even if your SD card, USB port, or modem are ruined you can use wifi and a program like Filezilla to get the archives off of your dying N900
to re-initialize

NOTE: Always flash the eMMC image first, then the FIASCO image immediately after that. Never boot up the device between flashing the FIASCO image and the eMMC image! When flashing eMMC always also flash FIASCO rootfs - NEVER boot the device between the two flashes.

I used an Ubuntu 18.04 AMD64 laptop for this.
1-install flasher or 0xfff onto your computer
2-flash phone's EMMC via USB
3-Flash phone's FIASCO via USB
4-boot phone
4.5-if needed add software sources(included in the links below) to phone
5-install CSSU(thumb if you want) to phone
6-install Backup Manager to phone
7-Install kernel update(if you have kernel power, KERNELS MUST MATCH BACKUP) on phone
8-reboot and restore via Backupmenu from SD card restore file from old phone(or loaded to MyDocs over network)
9-transfer MyDocs contents via USB or over network SFTP/SCP

get the Nokia closed bin-blob flasher-3.5, this is the reference flasher used in most Nokia and TMO posts so this instruction will too(you probably want the 64 bit version at this late date unless you are still using a 32bit machine and OS, they also have a flasher for Unix Apple machines)
https://web.archive.org/web/20131117...env_downloads/ be sure it is flasher-3.5 for fremantle and not the flasher for harmattan
and install it
or if you like FOSS install 0xffff(Open Free Fiasco Firmware Flasher) directly from your software repo, in most Debian based distros just:
follow these instructions(thanks Pali)
https://talk.maemo.org/showthread.php?t=87996

how to flash(with old dead links look below for live)
https://wiki.maemo.org/Updating_the_firmware

get your firmware files from a live site
https://web.archive.org/web/20131117...ev/nokia_N900/
I start out with the first releases and then reflash with the last releases pulling out the battery and resetting after every flash
what I did, in exactly this order, you have to do the EMMC before you do a Vanilla file, this worked for me but the early release installs may not be required, I dont recall ever doing that in the past but I had a MD5 sum problem so wanted to get started with any firmware
RX-51_2009SE_1.2009.41-1.VANILLA_PR_EMMC_MR0_ARM.bin
RX-51_2009SE_1.2009.42-11_PR_COMBINED_MR0_ARM.bin
RX-51_2009SE_10.2010.13-2.VANILLA_PR_EMMC_MR0_ARM.bin
RX-51_2009SE_20.2010.36-2_PR_COMBINED_MR0_ARM.bin

do from linux terminal:
for example(and EXCLUSIVELY in this order!! if you hose your firmware and are stuck in bootloop see footnote at bottom):
and then
and boot with top button your phone with USB cable inserted into N900 and your computer(I used my USB 2.0 port) it will begin to spool through the wipes & installation
and once the CLI drops back to a prompt pull battery
but that is probably not necessary

the MD5 sums work like this in linux
md5sum filename.bin
will get you a number to compare to the list linked on the same page

flash and boot up
http://maemo.cloud-7.de/maemo5/et_al...ogs/BM.install

and click on 'BM.install'
this gets you to backupmenu
you will also get the option to install maemo update, do this!

you are not ready yet having installed a matching kernel and if you just jump to the newly installed backupmenu you will brick your n900 and need to go back to the start of these directions with flasher and your fiasco and vanilla images

next assuming you were using it already install CSSU
I was using CSSU-thumb
http://maemo.merlin1991.at/cssu/comm...mantle.install

these repos should get installed by the two links above so use them, but if they dont work here is how to add them manually.
then add extras-devel
In the Application Manager:

Navigate to the application menu (tap the title bar)
Select ‘Application catalogs’
Select ‘New’
Enter a catalog name of ‘Maemo extras-devel’
Enter a web address of http://repository.maemo.org/extras-devel/
Enter a distribution of ‘fremantle’ (‘fremantle-1.2’ and ‘fremantle-1.3’ now have the same content)
Enter components of ‘free non-free’
Select ‘Save’

and add extras-testing
Navigate to the application menu (tap the title bar)
Select ‘Application catalogs’
Select ‘New’
Enter a catalog name of ‘Maemo extras-testing’
Enter a web address of http://repository.maemo.org/extras-testing/
Enter a distribution of ‘fremantle’ (‘fremantle-1.2’ and ‘fremantle-1.3’ now have the same content)
Enter components of ‘free non-free’
Select ‘Save’


for both the CSSU(I have CSSU thumb) and Backupmanager install links it is easy to just dump them onto the new phone and then click on them in file manager,

It is important to install kernel-power-settings(kernel power 53) too if you were using it as without it this will hang your boot and leave you soft-bricked your N900 needs the same kernel that you were running when you made your backupmanager backup files. As we like to not remember install manager takes FOREVER!

Once you have both installed including all reboots you can do a final reboot with the keyboard popped out, it will give you the usual options, choose backupmanager, find the backup files for both root and optfs and get your old N900 setup back(may require moving some required files off of old phone mydocs too such as Sygic maps or dictionary files)

Now for completeness, I recall there was a way to package backups for kernel, root, and optfs into something you can flash clone in one go without ever having to do any boot-up; simply clone/restore the whole phone over a USB cable but I think it was Joerg who knew how you can probably search .
If you are swapping out hardware keyboard layouts be sure to go into settings-text input and change to the correct layout map.
Wow, I had forgotten how slow the application manager works, especially before overclocking and swap improvements!!
I think AppMan took more time to do it's thing than hunting all of the files and settings I needed to get to backupmanager bootstrap readiness.
Big thanks for Maemish for hooking me up with a great deal on a beautiful replacement N900 at this late date in our history.
please forgive spelling and format, I took notes in gedit and didnt spellcheck/was distracted.
As I said above this is not necessarily a best way; just one that I have personally used today to clone over from my old to a new N900.

Did you hose your firmware or screw up the order? Do you get the little N900 and a wrench instead of just a NOKIA splash screen at bootloader splash screen? Try cold flashing. If you use flasher-3.5 to switch your phone the N900 to devlopment mode the phone will display the hardware info you need as well as kernel version.
http://wiki.maemo.org/Updating_the_f.../Cold_Flashing

flasher-3.5 -h <RX-51 should describe most n900s>:<hardware number> -F RX-51_2009SE_20.2010.36-2_PR_COMBINED_MR0_ARM.bin -c -S usb
for example my Scandinavian N900 is a hardware 2404 though 2101 is supposed to be more common