Troubleshoot

Service failed

Stop service and process

sudo /etc/init.d/mysql stop
sudo systemctl stop mysql
sudo killall -KILL mysql mysqld_safe mysqld

Start service

sudo /etc/init.d/mysql start
sudo systemctl start mysql

Backup database before cleanup

sudo apt autoremove --purge mysql-server\* mariadb-server\*
sudo rm -rf /var/lib/mysql
sudo rm -rf /etc/mysql/

Re-install

sudo mkdir -p /etc/mysql/conf.d
sudo apt install -y mysql-server