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Old 11-19-2005, 04:34 PM   #1
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Distinguish between crash and reboot

Hello everybody. I'm doing some kind of work where I need to determine from an external point of view if a machine crashed or rebooted: to explain what I mean I'll give you an example. Let's say that there's a computer in a room connected to the network; I can access that computer from the network but I can't enter the room where the computer is. Now: there's a man in the room who can crash the computer (for example by unplugging the power cable) or just reboot it.

To figure out an answer to this question, I was thinking about the behavior of fsck at the very beginning of the startup process: that program knows in some way if the disks were properly or unproperly unmounted. Where does he gather that information from? And: is there any way I can access that information when the machine is booted and ready, or does fsck "delete" that information? Or do you have any other suggestion to solve the same problem?

Thanks to anybody for reading.
Old 11-20-2005, 06:08 AM   #2
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The information fsck reads is stored outside of filesystem. Think of it as one bit which is set when partition is mounted and unset when unmounted. Clearly not useful for you.
Try reading /var/log/messages.
Old 11-20-2005, 03:10 PM   #3
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Reboots are intentional, crashes aren't. Unless a person deliberately chose to reboot the machine in question, it was a crash. I'd agree with Emerson that a useful first place to look would be /var/log/messages
Old 11-21-2005, 10:42 PM   #4
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Basically, if you look at /var/log/messages, you will see startup code every time the machine boots, whether it was a crash or a reboot, but you will only see shutdown code for intentional reboots. You can sometimes infer crashes from boot messages, but the real giveaway is seeing Kxx scripts running from the rc directories; these are run during a shutdown to kill processes. To see what scripts I'm talking about, check /etc/init.d/rc2.d (this path may vary slightly) for instance, there are Kxx scripts and Sxx scripts. The S scripts are for startup, and the K scripts are for shutdown. They are usually links that point at files in /etc/init.d and the same script is used for startup and shutdown of a subsystem, but the S script gets a 'start' parameter added to it, and the K script gets a 'stop' parameter.

Hope this answers your question.

Old 11-26-2005, 06:25 PM   #5
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thanks guys for your answer. I'd like to know if there's a different solution, though: I mean one that doesn't use log files, or uses log files that are accessible by everybody. The problem is still the same: determine if the last boot was a reboot/shutdown or a crash. I was wondering if reading dmesg and looking for some string can be a decent solution.




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