Can’t login as root to PHPMyAdmin on new server install

Background

After installing a new server, or doing a server migration, you find you can’t suddenly can’t log into PHPMyAdmin as root anymore.

The errors are:

Cannot log in to the MySQL server

and

mysqli_real_connect(): (HY000/1698): Access denied for user 'root'@'localhost'

In MySQL 5.7 (released Oct 2015) and MySQL 8, the root MySQL user is set to authenticate using the auth_socket or caching_sha2_password plugin rather than with mysql_native_password. This will prevent programs like phpMyAdmin from logging in with the root account.

Create a New Superuser for phpMyAdmin

First

sudo mysql -p -u root

then

CREATE USER 'pmauser'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password_here';

then

GRANT ALL PRIVILEGES ON *.* TO 'pmauser'@'localhost';

Reference

Can’t log into phpMyAdmin: mysqli_real_connect(): (HY000/1698): Access denied for user ‘root’@’localhost’