Fairphone 2 Ubuntu Touch

I had problems following the firs post Manual.
In point 4 theres no description where to do “adb shell mount /cache” im in Recovery Mode of Ubports I wasn’t able to find a terminal in the recovery. And from my Laptop i didn’t have connection to the phone over adb. adb devices list is empty. I added the line below to the file: /etc/udev/rules.d/android.rules
SUBSYSTEMS==“usb”, ATTRS{idVendor}==“2ae5”, ATTRS{idProduct}==“9015”, GROUP=“users”, MODE="0666"
then i got connection. Maybe @wouterx can add that to the manual…

Now connected over adb to the phone i get this message:
$ adb shell mount /cache
mount: mounting /dev/block/platform/msm_sdcc.1/by-name/cache on /cache failed: Device or resource busy

How can i get over that, i have no clue…
Regards, Novski