# Why do notebooks reset themselves now and then? [closed]

Now and then I am working on a notebook and suddenly it reset itself. What I mean is that I am entering commands and when I type enter, the notebook command number goes to 1 and I have lost all definitions of functions I have made previously. It is annoying since I have to go back and resubmit all my definitions. I have not noticed anything special about the instances when this happens. I am using version 9.0.1.0 and I am running it on a MacBook with Mac OS X, 32 bit and 64 bit kernel.

As far as I could tell I did not click on any special key (the command, alt, control or fn keys) and I don't see any patter to when this happens. It happens now and then (I do calculations every day and this happens every 3-4 days, unexpectedly).

Does someone have an idea what provokes this?

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• It happens to everybody, although some operating systems/versions of Mathematica are more prone to it. It is known as a "kernel crash", and there is not much you can do to prevent it other than avoiding certain functions that you know from experience will cause it to happen. For example, for a previous version of Mathematica ListAnimate with lots of frames was such a function for me. I'm sure Wolfram Research is working hard at improving the stability of Mathematica so that this will happen as rarely as possible. – C. E. Oct 3 '15 at 0:28
• It might just be my user superstition, but I think I detect a slight bit more motivation on the part of Wolfram to look into and perhaps even fix things that result in kernel crashes than I do in some other aspects of mathematics that they might consider open to interpretation. But to get that motivation certainly requires reporting a repeatable example. So, if there is something about the way that you are using Mathematica that results in kernel crashes every 3-4 days and you can start keeping track of what you are doing and pinpoint causes then you and the rest of us might all benefit. – Bill Oct 3 '15 at 2:10
• I have the impression that certain out-of-memory cases may cause this phenomenon as well. If this concerns you it may be useful to track your memory use with a systems resource monitor. – Sjoerd C. de Vries Oct 3 '15 at 7:15