Shrinking home and extending root partition

Good evening,
I actually wanted to finally do it tonight, but I can’t reach the Sony with fastboot. The problem is that I can’t switch the network to the USB port with dhclient. I have used these instructions: https://forum.sailfishos.org/t/resizing-root-directory-telnet-connection-problems/7067/3?u=olf

I get the following from my linux console (opensuse LEAP 15.6)

fastboot boot hybris-recovery.img 
Sending 'boot.img' (22676 KB)                      FAILED (Write to device failed (No such file or directory))
fastboot: error: Command failed

fastboot devices
CQ300043MN       fastboot

dhclient CQ300043MN
Device "CQ300043MN" does not exist.
Cannot find device "CQ300043MN"

What am I doing wrong?

I will probably try again on Saturday evening.