FreeBSD 4.x crash system

[Vincent Blondel]

Hi,

System : FreeBSD 4.10-RELEASE-p2
Host : Tyan Thunder K7X (S2468GN)
Cpu  : 2 * Athlon MP 1800+
Memory : 2 * 512Mb DDR-266 Memory
Adaptec 5400s SCSI RAID Controller

I got for the second time, this week, a system crash with my FreeBSD server. You
can find below what I get on the screen but I don't understand all what it means.
I just see there was a problem with the process imapd ( previous time I got a
segmentation fault with apache 1.3 )

fault code           = supervisor read, page not present
instruction pointer  = 0x8:0xc02a3e90
stack pointer        = 0x10:0xe3b22a10
frame pointer        = 0x10:0xe3b22a14
code segment         = base 0x10, limit 0xfffff, type 0x1b
                     = DPL 0, press 1, def32 1, gran 1
processor eflags     = interrupt enabled, resume, IOPL = 0
current process      = 76856 (imapd)
interrupt mask       = none <- SMP: xxx
      kernel : type 12 trap, code=0
db>

I also remarked the keyboard focused on a process with 'db>'. What is this and what can
I do with it. I tried 'exit' 'quit' 'bye' but all these statements don't do anything so I
just pressed on button 'Reset' and rebooted the machine.

Before starting the machine I checked the hardware by running 'memtest' during 6 hours and
no errors were found. This seems to point the problem with my FreeBSD installation better
than a hardware ( example memory ) error.

I also don't pretend my system is compiled with the best method. I remember ( this is
now a log time ago ... ) I compiled lot of things with '-O2 -pipe' ( except the
kernel with '-O -pipe' ) but is this safe enough for an SMP system with FreeBSD 4.x ???

So can somebody explain me what does this mean and also if I have to configure
something to make a dump file when I get an error. I suppose this will be
easier to investigate the problem if I still have other system crash.

Regards
Vincent.