cvs commit: src/sys/alpha/alpha support.s src/sys/i386/i386 swtch.s src/sys/kern kern_shutdown.c src/sys/sys systm.h

M. Warner Losh imp at
Tue Jan 20 20:08:51 PST 2004

In message: <Pine.NEB.3.96L.1040120221452.53972J-100000 at>
            Robert Watson <rwatson at> writes:
: On Tue, 20 Jan 2004, Don Lewis wrote:
: > It would be extremely helpful to preserve the panic message and
: > (optionally) the backtrace across the reboot.  Crash dumps may not
: > always be possible for any number of reasons (swap smaller than RAM,
: > /var/crash too small or overflowing with previous crash dumps, crash
: > dump takes too long ...).  This is especially true in cases where the
: > machine crashes and reboots unattended. 
: Actually, I was having a very similar conversation with Bill Paul this
: afternoon.  We were discussing dropping a copy of the kernel message
: buffer onto the header of swap space on panic, if possible, and then
: dropping them in /var/log/crash.log for management by newsyslog.  Then the
: natural response to "My machine spontaneously reboots" becomes "Look for
: something recent in /var/log/crash.log", as opposed to "You'll need to
: enable crash dumps, set up a serial console", etc.  It's also something we
: could turn on by default, as opposed to crash dumps, which would otherwise
: consume of alot of disk space.

I assume you are talking about reading them out of swap space on boot
so you'd see something like the following in your logs:

<date-time> foo: first reboot after kernel panic

Right?  Then the message would be zeroed out, so you don't get it on a
normal reboot, right?


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