User vs Kernel mode

Greg 'groggy' Lehey grog at
Tue Oct 17 04:32:21 UTC 2006

On Tuesday, 17 October 2006 at  9:52:17 +0700, Olivier Nicole wrote:
>> Processes always start in kernel mode, because they're started by the
>> kernel.  They typically spend most of their time in kernel mode (for
>> example, whenever they're idle or waiting for I/O).  An active process
>> may switch back and forward between kernel mode and user mode
>> thousands of times a second.
> Thanks for the clarification.
>> Maybe you should describe your problem.
> The application has been working fine for almost 3 years, along with
> Apache, going through RELENG upgrade without problem.
> Now I start noticing that Apache hangs (sig 11),

A hang is when the system stops reacting.  Signal 11 is not a hang:
it's a segmentation violation, which means that the program has
performed a specific kind of illegal operation.

In the case of a program that used to work well, this almost
invariably means that you have hardware problems.

> 2 options:
> - I added memory in the machine and the meory is causing problems.

Yes, this is possible

> - I changed my application a little bit and it started eating
>   other processes.

This is less likely.

> So I'd like to be sure that my application cannot eat other
> processes, so i could eliminate one cause.

Don't even think about this at the moment.  If you have just installed
new memory and these problems occur, try taking it out again and
seeing if the problem goes away.

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