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I had only 1 interface. udev created a new interface (eth1), so I deleted the (old) interface and renamed eth1 as eth0 in the persistent-net.rules...
nop... that didn't work either :'( At this point, it would've been better to just start a new VM from scratch, but that was not the idea......
No, I was not running the original VM, and yes, I did check that the MAC address of the new VM is different from the original :-) still no luck...
I've just cloned a working VM (running debian, using shared networking, static address) but the new VM has problems when trying to configure eth0:...
