How to change the mysql root password
One option is to save UPDATE mysql.user SET Password=PASSWORD('newpass') WHERE User='root'; into a file and then manually start mysqld with --init-file=FILENAME. Once the server starts, it should reset your password, and then you should be able to log in. After this, you should shut down the server and start it normally.
A little late to the game, but I had the same issue on a raspberry pi install and found out that it needs elevation. Adding a sudo to the front of the password change allowed it to work.
sudo mysqladmin -u root password 'newpass'followed by an elevated sql access
sudo mysql -u root -p If either are not run as sudo, it will fail.