Jailbreaking has its many benefits, but there’s always a risk that installing a certain tweak or app from Cydia will cause something in iOS to go haywire. It doesn’t happen often, but when it does you want to be able to fix the problem without having to restore and lose your jailbreak.
Luckily, there’s a relatively easy way to troubleshoot your jailbroken iOS device and find out the exact tweak that’s causing the problem.
MobileSubstrate is kind of like the backbone of a jailbroken iPhone or iPad. It’s the framework developers use to hook in extensions and tweaks you install from Cydia. In a recent update, the creator of Cydia, Jay ‘saurik’ Freeman, added a nice new feature that makes it easy to troubleshoot:
"As of version 0.9.3997, you can now disable Substrate entirely by holding down Volume Up as the device boots.This feature allows you to bypass horribly broken extensions (ones that prevent the device from starting up at all) that you may have installed so you can open Cydia and uninstall them.To support devices that do not have a Volume Up button (the first-generation iPod touch), you can alternatively hold down the “Clicker” (not Volume Up) button on your headset or earphones."
You should already have this latest version of MobileSubstrate, so you’ll be able to use the disable feature right now. If your iPhone is constantly crashing or you think a certain tweak is causing something in iOS to act up, reboot your device by holding the Home and power buttons simultaneously until you see the Apple logo.
Once the logo appears, hold down the volume button like the instructions say and you’ll enter into Safe Mode. This means that all of your jailbreak tweaks and extensions are turned off, making it easy for you to go into Cydia and remove the packages that are causing the problem. If you’re not sure what tweak is responsible, then you’ll have to try uninstalling and rebooting until you notice the problem go away. It’s not a full-proof way to troubleshoot, but it’s not bad for a free, built-in solution.