Some systems like Ubuntu, mysql is using by default the UNIX auth_socket plugin.

Basically means that: db_users using it, will be "auth" by the system user credentias. You can see if your root user is set up like this by doing the following:

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

mysql> USE mysql;

mysql> SELECT User, Host, plugin FROM mysql.user;

+------------------+-----------------------+

| User             | plugin                |

+------------------+-----------------------+

| root             | auth_socket           |

| mysql.sys        | mysql_native_password |

| debian-sys-maint | mysql_native_password |

+------------------+-----------------------+

As you can see in the query, the root user is using the auth_socket plugin

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