How Do Sites Keep Their SQL Passwords?

I am working on a site and I am using MySQL. I have a file that accesses the database with a password. Right now the password is just saved in plain text in the file but as you guys should know this is not secure. What is the best way of having this be secure? Or should I just make sure the permissions are locked down on it? Obviously sites that use SQL should have a password on their SQL servers but how do they securely do so?