Ubuntu, recover root password

You need to load into recovery mode

Then into root shell

Then run passwd root command to change root password.

Check output of passwd command.

If u see something like: Authentication token manipulation error

Try run pwconv command, it should fix this (problem is that passwd and shadow files are not synced)

If pwconv fails with message like: cannot lock /etc/passwd; try again later

There can be two problems, try to find and delete passwd.lock file.

Or in my case, remount file system to have write access with command: mount -o remount,rw /

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