C:\Program Files\MariaDB 10.2\bin>mysql admin -u root password "x123456789"
mysql Ver 15.1 Distrib 10.2.4-MariaDB, for Win64 (AMD64)
Copyright (c) 2000, 2016, Oracle, MariaDB Corporation Ab and others.
C:\Program Files\MariaDB 10.2\bin>mysql -u root -p
Enter password: **********
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 14
Server version: 10.2.4-MariaDB mariadb.org binary distribution
Copyright (c) 2000, 2016, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> set password for 'root'@'localhost'=password('x123456789');
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)