Переустановка пароля root mysql

# sudo service mysql stop
# sudo mysqld_safe --skip-grant-tables &
# sudo mysql -u root
mysql> use mysql;
mysql> update user set authentication_string=PASSWORD("YOUR-NEW-ROOT-PASSWORD") where User='root';
mysql> flush privileges;
mysql> quit
# sudo service mysql stop
# sudo service mysql start
# sudo mysql -u root -p

создать /var/run/mysqld 

sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf

default_authentication_plugin   = mysql_native_password
 

см /var/log/mysql/error.log