The updated mobile substrate version 0.9.3997 by Saurik could save you from restoring your device if a jailbreak app or tweak you recently installed went horribly wrong.
For iPhone newbies out there – Saurik (Jay Freeman) is the creator and the mastermind behind Cydia. What’s a Mobile Substrate? Essentially it’s a few system shared dynamic libraries (.dylib files, similar to Windows .DLLs a.k.a system files) that allows developers to write programs that extend programs they didn’t write. Many jailbreak apps you’ve heard or installed before such as Winterboard, QuickGold, SBSettings, Five Icon Dock, Clippy, Backgrounder and even ultrasn0w unlock require mobile substrate to run properly.
He just released the latest version of Mobile Substrate which allows you to boot up your iPhone safely if one of the jailbreak apps and tweaks you just installed caused your iPhone to crash or stuck in a boot loop. A crash like this might force you to restore your iPhone and potentially you may also end up losing your jailbreak. iPhone 4S users who are currently jailbroken on iOS 5.0.1, this is really for you!
According to Saurik:
“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.”
If you’re a jailbreak who constantly installs Cydia apps and tweaks, it’s best that you update your mobile substrate now.
Once installed, by simply holding the ‘volume up’ button on your iPhone during reboot will bypass any error. You can then safely remove the problematic app or tweak you just installed.
This is a great tweak that every jailbreaker should install. How to update this? Just launch Cydia and tap on Changes. You should see it there.