I'm using a backup internet connection on my Pi (using latest Raspbian) where bandwidth is very expensive (let's say a roamed 3G connection in a foreign country). I thus want to configure my Pi as follows:
- Don't consume any internet bandwidth without notice (or explicitly knowing about).
- Especially, don't automatically download any system or software updates.
- Don't run any background processes which will connect to the internet and consume bandwidth.
- One exception: obtaining the current system time via NTP from a time server is OK.
Which system settings do I have to change for that? Do I need to configure (or maybe even remove) some of the pre-installed software which will otherwise connect to the internet sometimes?