En arrêtant la base (https://mariadb.com/blog/how-reset-root-password-mariadb-linux)

1. stop mysql

2. reset password

mysqld_safe --skip-grant-tables --skip-networking &
mysql -u root
mysql> use mysql;
mysql> alter root IDENTIFIED BY "new-password";
mysql> alter user squash@localhost IDENTIFIED BY "new-password";
mysql> flush privileges;
mysql> exit

3. mysql restart

mysqladmin

mysqladmin -u root -pCURRENTPASSWORD password <nouveau>