obtaining a kernel crash dump

[Andrew Gallatin]

Nick Strebkov writes:
 > May 19 16:17:00 devel /kernel: 
 > May 19 16:17:00 devel /kernel: syncing disks... 60 3 2 
 > 
 > [dd boot kernel messages]

Try disabling sync-on-panic.  It almost always causes problems for me
when trying to get dumps.  

% cat /etc/sysctl.conf 
kern.sync_on_panic=0

If you are running a newer version of FreeBSD with the DDB_TRACE
options, you want to enable DDB and DDB_TRACE.  This will get you a
stack trace on console, which is a heck of a lot better than nothing
if your crashdumps don't work.

options         DDB                     #Enable the kernel debugger
options         DDB_TRACE


Sometimes I have problems getting a dump on 5.x if I've dropped into
ddb, so I use the following to prevent the system from dropping to a
DDB prompt at panic:

options         DDB_UNATTENDED



Drew