App store id different from OSX system id? My dad also has a macbook and he now has a strange problem. He knows the password for the app store with which he can install new apps. I verified that works. But when I wants to install an app by double clicking a .pkg file (for google earth) he is asked the system password. I always assumed this is the same as the password for the app store, but to my surprise, the same password doesn't work.

I checked on the terminal by entering sudo ls and trying the password which works in the app store, but that fails. I am 100% sure I type the same password, and also tried copy pasting the password.

Does anybody know where I'm going wrong here? How can the password for the app store be different from the system password? All tips are welcome!
You're talking about the password for a specific Apple ID (which you use on the App Store), versus the password for a specific user account on the Mac. There's no requirement anywhere that they have to be the same.

Your dad probably used a different password for his user account. If you cannot remember it, you can reset it by following the instructions here:

https://support.apple.com/en-us/HT202860