Database Software

I try to connect two databases,

In: "All Initialization Parameters" i set: "global_names = false"

I do databases link from Enterprise Manager Console.
Create database Link:
Name: db_name.servicename (I take names from All Initialization Parameters)
User/Password: sys/****
Service Name: servicenames (I take it from All Initialization Parameters)

"Databases Link created successfully"

And when I push test button: "The Database Link is not active"

Thanks for any help.