i enter "rm -rf /obj" and my system is broked
Solution 1:
The photo shows that even /bin/sh isn't found, starting DNS resolution fails, even mounting file systems fail.
As @golimar already said, /obj is not part of any standard Linux installation. It's not part of Ubuntu either. However /bin is, and /bin/sh always exists unless you delete it. To me it looks like you've actually deleted one or more standard Linux root directories. The most sensible way forward is to just create a new VM.