I would like to install a persitent linux on my N9 (64G)
with the help of gparted and use it as an external hdd

i.e. boot my notebook from my N9 via USB without losing
any functionality of my N9

Has anyone done it ? Any pitfalls ?

It's interesting, but no idea, sorry.

I was seeing other did with a raspberry pi + lapdock motorola
http://liliputing.com/2012/06/turn-a...a-lapdock.html

And this other
https://blog.adafruit.com/2015/01/16...-raspberry_pi/

i had done something similar, but it required the phone to be switched off for booting the desktop linux as mbr on n9 did that, and so the entire N9 mmc had to be exported to the pc.

I guess there is a way of achieving what you want, but i couldn't do it.
You can squeeze out a partition from your MyDocs partition. And use it to store the desktop linux.
Use this guide for repartitioning or gparted (You will have to export the entire device first to n9 either using ubiboot or by loading the rescue initrd).

After partitioning and installing linux using EFI. You have to export this partition to pc whenever USB is connected, a way of doing this is given in the repartitioning thread, but i couldn't get it done .
Then once that is exported, i guess you can specify what EFI file to boot from on the pc and it should boot without having to turn off the phone.

isnt n9 have some iso to mount in some mode, so you can just replace that iso?

I think one of the hurdles is timing.
When I connect the N9 to my notebook and turn on the notebook,
I can choose "Use as mass storage" after a couple of seconds on
my N9.
I can then press a key (ESC in my case) on my notebook for selecting
the boot device.
So the bios has to do a scan of USB-ports between selecting mass storage
on my N9 and pressing ESC on my notebook.

Unfortunately my N9 is the only phone I've got, so I don't want to brick it.
That's why I'm asking whether anyone has tried it.

Is there a way to put the N9 into mass storage mode by command or does
it have to have a signal on the USB-port for mass storage mode ?

You can change the USB-Service fix to mass storage or all the other option.
What you have now is "always ask"

Control - Assesoirs - USB

That might be quick enough, but if it isn't there is an alternative you can try.

Normally when there is no USB connection active, the usb_moded daemon removes the driver modules from kernel. When you need to have IP connection to the device, the module g_ether.ko is loaded, and when you need USB storage connection, the module g_file_storage.ko is loaded.

If you disable usb_moded and load g_file_storage.ko before connecting the USB to the device you'll have the drive emulation working immediately.

Thanks everybody for your help and support.

At the moment I'm stuck with the partitioning part following the link
mentioned by tioubxancur.

I can follow the instructions on my N9, but the text is too small and
the wraparounds are annoying. So I tried to connect to the N9 via
ssh - works for "user" but not for "root" - can't login as root.
As "user" I don't have permissions.
So I will have to do some reading and trying.
Maybe exporting the MMC to my linux box is easier because I can
use gparted, but I have never done that.
Any suggestions ?

OT: I got my Jolla tablet today so I'm stuck between work and a honey pot

I did it by exporting it and then using gparted. I had used gparted a lot before and i am more comfortable with it than the command line.

As for the root over ssh, login in as user and do:
$devel-su
and default password is rootme