I lost the credentials to the Ubuntu 20.04 LTS Server. I need the instructions on how I could log into a Linux host without knowing a valid login/password combination, and without permanently altering any local files.
Usually the part between the colons ":". to the mounted filesystem. Then reboot.
There are more detailed instructions around the web, but you will have to change these files.
No way around it that I know of. Once you can login again. Reset your passwd again.