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My iPhone 4 runs iOS 5.0.1 and is jailbroken. It has recently become unstable: it often crashes and restarts in safe mode. Then, in safe mode, I can choose to restart and it will often go right back into safe mode again. Clearly, some little cog has come loose inside.

I haven't found a definitive action that always causes a crash. They occur sporadically, but they occur most often when I am trying to purchase or upgrade an item in the App Store.

How can I discover what causes the crashes?

Is there a more elegant way to determine it than going into Cydia's list of installed packages and uninstalling the topmost one; then wait and see if it's stable now; otherwise uninstall the now-topmost package? This would probably work out eventually but it's certainly neither fun nor efficient.

No, I don't keep a list of which package was installed at what date. That would make it easier to roll back a month at a time.

Permanently reverting to a non-jailbroken device is not an option for me. The Cydia tweaks are way too convenient.

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The first thing that I would do is to check in the iPhones Diagnostics reports. In Preferences go to General>About>Diagnostics & Usage. There might be information about your crash there. Your other option is to install Crash Reporter and syslogd from Cydia. You would be able to get some information about crashes there. If you're having trouble even getting to Cydia, try disabling MobileSubstrate, those plugins tend to cause a lot of crashes on jailbroken devices.

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Thank you. It seems to be related to low memory. I thought that iOS would automatically free up memory and turn off apps as needed, but apparently something is hogging the memory. –  Torben Gundtofte-Bruun Mar 15 '12 at 6:44
    
Low memory may be the cause and I'm not surprised but that's not what's crashing. Something isn't handling the low memory situation well. iOS does free memory when it's in that situation but it does so by unloading some applications and it's likely that one of your apps or jailbreak tweaks doesn't like that. I don't know if jailbreak tweaks and apps are subject to the same memory freeing as app store apps but i think it's probably worth looking into more. Crash Reporter from Cydia will tell you what crashed not just the Low memory reports –  cafhacker Mar 15 '12 at 12:47
    
The only time my JailBroken iPod4,1 running iOS 5.0.1 crashes is due to a lack of memory. I check my crash logs often, and they're all labeled LowMemory. You can see what's hogging the memory by clicking on the log and inspecting it. There is a list of processes that were running at the time of the crash. The number listed next the them is the amount of RAM pages that process was using. However, the iPhone 4 has quite a bit more memory than the iPods, so you're probably dealing with a poorly programmed tweak (especially if SpringBoard was the one using the most memory). –  Andrew Larsson Mar 16 '12 at 21:34
    
You can also read this thread on Reddit: Tutorial: How to Figure Out What's Causing Your Device to Crash –  j0k Jun 29 at 12:36
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