Questions: What is DFU? And does installing the latest updates work the same as a reinstall? Or I still need to do a total reinstall? And should I reinstall the latest update or stick with 11.1? And for the reinstall, is iCloud backup/device wipe/iCloud restore recommended? And what method to use to wipe the phone? Thank you all! This has been a helpful thread and hopefully will work.
Hi,
DFU mode is Device Firmware Update mode. Basically it's as close to a format and re-install as you can get in the iOS world. It bypasses the boot loader and re-creates everything it's possible to re-create from scratch, essentially over-writing the current contents of your iPhone's OS storage with a clean OS image. It's not actually as scary as it might sound, however, and is an entirely Apple-supported method of re-installing iOS via iTunes.
The basic procedure would be:
1. Connect your iPhone up to iTunes in the normal way.
2. Whilst still connected to iTunes, hold down the power and home buttons on your iPhone simultaneously.
3. Keep holding both buttons for ten seconds. You will find after a few seconds the screen goes blank.
4. After the ten seconds have elapsed, let go of the power button, but keep holding the home button.
5. iTunes should eventually report it has found a device in Recovery Mode, but the screen of your iPhone will stay blank.
At that point, you can let go of the home button on your phone. In iTunes, click the Restore button, and iTunes will re-install your iPhone. Note that this will entirely wipe everything in local storage, and basically make your iPhone factory-fresh again. So if you want to keep anything that's currently on it, make sure you have a known good backup before doing any of this. Once the iPhone is re-installed you'll have an option of restoring either an iTunes or iCloud backup, or setting your iPhone up as new.
Hope this helps !