a few minutes ago I changed my Ubuntu user password. Then I turned off the computer and turned it on. After I entered the new password, the system would tell me that the password was wrong. I tried to enter the old password, but without success. Now, I can't log into my computer and I can't even reset my password. What can I do?
You can do it from recovery mode.
Reboot from lock screen.
Press esc while rebooting.
Go to Advanced Options for Ubuntu.
Go to Ubuntu, with Linux 4.##-generic (recovery mode).
Got to root.
Now execute the following commands...
Remount root with write access.
mount -rw -o remount /
It should not output anything.
Remember your username from the list.
Change your password.
Type your new password and Press Enter.
Exit the terminal.