swapon running before savecore (was Re: RELENG_6 kernel panic + savecore(8) problem)

Antony Mawer fbsd-stable at mawer.org
Thu Nov 29 17:42:06 PST 2007

On 26/11/2007 1:33 PM, Jeremy Chadwick wrote:
> On Sun, Nov 25, 2007 at 06:21:36PM -0800, Jeremy Chadwick wrote:
>> I believe the problem is that /etc/rc.d/swap1 is being run before
>> savecore.  I'm guessing that swapon(8) actually destroys/clobbers the
>> existing saved kernel panic/core data, thus one will never get a
>> coredump in /var/crash.  I believe some re-organisation of rcorder(8)
>> arguments in the files is in order, but I don't know what should
>> be changed to what.
>> I'll submit a PR for the above, because IMHO that's a serious one.
> PR 118255 has been opened for this matter.
> http://www.freebsd.org/cgi/query-pr.cgi?pr=118255

There seems to be conflicting information about what constitutes the 
correct behaviour here. The original 4.4BSD "Unix System Manager's 
Manual (SMM)", found here:


Indicates the following (found under the "System dumps" heading):

     - Kernel dumps write from the end of swap and work backwards
     - The kernel uses swap from the front and works forward
     - This way it reduces the chance of swapping overwriting the dump
        during the boot process until savecore is run

This somewhat more modern posting suggests that is still the case:


However the FreeBSD Developers' Handbook suggests a behaviour that does 
not match the current reality:


Can anyone speak with more authority on this...?


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