Cydia is confusing enough as it is, but when it starts throwing you cryptic errors, it can get even more frustrating. Here's a simple way to fix Cydia when it won't download any packages.
Sometimes, Cydia just starts throwing you an error that says:
I wasn't able to locate file for the sbsettings package. This might mean you need to manually fix this package.
netdb: open nodename nor servname provided, or not known
Luckily, there's a simple solution. Just head to your iPhone's Settings app, go to General, and scroll down to Reset. Tap the "Reset Network Settings" button, re-connect to your Wi-Fi (if applicable), and head back to Cydia. You should find that everything works again.
Unfortunately, this clears all your remembered Wi-Fi networks and their passwords, but it's a small price to pay for getting Cydia working again. I couldn't replicate the error to try other solutions, but the network reset solution worked perfectly for me. Check out the video above to see a quick walkthrough.