There are 2 ways to solve this:

1. You can set the root user to use the mysql_native_password plugin
2. You can create a new db_user with you system_user (recommended)

Option 1:

$ sudo mysql -u root # I had to use "sudo" since is new installation

mysql> USE mysql;
mysql> UPDATE user SET plugin='mysql_native_password' WHERE User='root';
mysql> FLUSH PRIVILEGES;
mysql> exit;

$ service mysql restart

Option 2: (replace YOUR_SYSTEM_USER with the username you have)

$ sudo mysql -u root # I had to use "sudo" since is new installation

mysql> USE mysql;
mysql> CREATE USER 'YOUR_SYSTEM_USER'@'localhost' IDENTIFIED BY '';
mysql> GRANT ALL PRIVILEGES ON *.* TO 'YOUR_SYSTEM_USER'@'localhost';
mysql> UPDATE user SET plugin='auth_socket' WHERE User='YOUR_SYSTEM_USER';
mysql> FLUSH PRIVILEGES;
mysql> exit;

$ service mysql restart

账号初始化：

$ sudo mysql_secure_installation

默认root密码为空；然后设置root密码和其他选项：

- Set root password? [Y/n] y
- Remove anonymous users? [Y/n] y
- Disallow root login remotely? [Y/n] y
- Remove test database and access to it? [Y/n] y
- Reload privilege tables now? [Y/n] y

登陆MariaDB命令行：

$ sudo mysql -u root -p