I have no account in ubuntu

I just bought a new laptop with ubuntu installed on it. When i first turned on the laptop ubuntu started with an error and restarted. Then when it turned on again i only had the guest session option. I've tried, but i can't use sudo in the terminal: Sudo: unable to change to root gid: operation not permitted Sudo: unable to initialize policy plugin I tried the recovery path too, but i don't have a username and can't do anything. I can only go in guest session. Please help, sorry if this is something obvious to do, it's my first time opening ubuntu.

reset root password :

While boot press shift and choose recovery mode :

drop to root shell then use following commands :

mount -o rw,remount /
passwd root

to add new user use :

adduser username

and choose a password for the user

finally:

reboot