What is an 'app'?
- An app (short for 'application') is stand-alone software that runs on your device, has its own GUI (interface), and (except for SpringBoard) has its own icon on the iOS home screen.
- Examples of apps:
- Everything downloaded from Apple's App Store.
- The default iOS software: Mail, Phone, Safari, etc.
- SpringBoard (the iOS 'home screen').
- Some Cydia packages, including: iFile, Cycorder, Cydia itself.
What is an 'extension'?
- An extension (also called 'tweak' or 'add-on') is software that extends (or modifies) an app; an extension can add new features to an app or change the way that an app behaves.
- This is similar to the idea of extensions for popular web browsers (Firefox, Chrome, Safari, etc.).
- Examples of extensions:
- Several Cydia packages, including: WinterBoard, SBSettings, Backgrounder, FolderEnhancer.
What is 'Safe Mode'?
- Safe Mode is a feature provided by MobileSubstrate, a special piece of software used by many extensions.
- Safe Mode is the same as normal mode, except that extensions are disabled.
- Apps will work just like they would on a non-jailbroken device.
Why is Safe Mode needed?
- Extensions modify apps. If there is a problem with an extension, it can cause the app that it modifies to crash.
- If that app is SpringBoard, it could crash over and over again, preventing you from using your device.
- Safe Mode prevents this; if SpringBoard crashes, it will be reloaded with all extensions turned off.
- You can then uninstall the offending extension and restart to return to normal mode.
How can extensions cause crashes?
- To make an extension, a developer has to carefully study the app that the extension will modify. Mistakes can happen.
- Anytime that an app is updated, the way that app works can change. This can break extensions, which can lead to crashes.
- A good example is SpringBoard, which tends to change with every new version of iOS; this often causes existing extensions to break.
- Multiple extensions might modify the same app. If these extensions are not designed to work together, it can lead to crashes.