I spent almost 3 days in total to solve this machine, but I’m happy that I have learnt some new things.
Thank you for creating this painful machine @MinatoTW and @egre55 - please make moar of these machines.
For root flag, some basic but useful advice that you may be bored of hearing;
- monitor
processes
andfile system changes
on the machines you get shell - enumerate files as much as you can
Good luck.