-- DEFAULT: Username:root , Password: – (none)
mysql> SET PASSWORD FOR root@localhost=PASSWORD('mypassword');
mysql> GRANT ALL PRIVILEGES ON *.* TO root@localhost
IDENTIFIED BY 'mypassword' WITH GRANT OPTION;
sudo -H edit /etc/dbconfig-common/phpmyadmin.conf
# This will open your phpmyadmin configurations.
# There, you will see your username under dbc_dbuser='your_username' and
# password under dbc_dbpass='your_password'.