How to Fix a NetDB Error in Cydia

1. Open iFile, iFunBox or Mobile Terminal on your iPhone or iPad. Open the 'System' folder.
2. Navigate to the '/private/etc/aptsources.list.d/cydia.list' folder. Delete the contents of that folder.
3. Find the '/private/var/lib/cydia/metadata.plist' file. Delete that file.
4. Reopen Cydia. Since you have removed any corrupted files, Cydia should open without incident. When Cydia opens, it recreates the system files and starts fresh.