Mobile Substrate 0.9.3997 updated
Cydia Runs on different set of procedure, Mobile Substrate is one of them that back Software apps & Cydia Tweaks. Sometime when some tweaks goes bad Mobile Substrate will save you & it will save you from restoring your device if something goes terribly wrong due to problematic jailbreak app or tweak.
[box type="info"] 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. [/box]
if you have jailbroken iOS device running iOS 5.0.1 or lower then install this Mobile Substrate update ASAP that will save you & avoid a restore your jailbroken iOS device after installing a problematic jailbreak app or tweak.
Be careful before installing new jailbreak apps or tweaks and read reviews