freebsd stable - Jan 2008 - dmesg : no output on 1 of 2 7-stable boxes

One of 2 laptops running 7-stable shows nothing with dmesg, (other is OK).
Needs fresh eyes please, as I've already checked all this:
   - Text is in /var/log/messages, readable to normal users.
   - df shows enough disc
   - I patched out all of loader.conf, except essential
hw.ata.ata_dma="0"
   	(that was to remove any *verbose* that might be overflowing
   - I tried loader.conf 	kern.msgbuf=64000	
   - Tried a Generic kernel
   - I've recompiled & installed dmesg & kernels
   - Haven't done a make world (slow box), but repeated make all ; make
install
     with each day's new source.
   - Both hosts running same /usr/src from yesterday:
           /pub/FreeBSD/development/CTM/src-7/src-7.0102.gz
           Jan 25 15:25 TZ=GMT+01:00
   - cd /etc;grep dmesg *
   	rc.conf:dmesg_enable="YES"      # Save dmesg(8) to
/var/run/dmesg.boot
   	Binary file rc.d matches	# Just the standard /etc/rc.d/dmesg
   	rc.local:/sbin/dmesg > /tmp/dmesg.rc.local
   	# -rw-r--r--  1 root  wheel  0 Jan 25 14:01 /tmp/dmesg.rc.local
   - mergemaster -sicvP 
Any ideas please ?
Julian
--
Julian Stacey.  Munich Consultant: BSD Linux Unix.  http://berklix.com

Hello Julian,

I'm sorry this is a late reply, but I noticed your post
on the freebsd-stable list just now.

Julian H. Stacey wrote:
 > One of 2 laptops running 7-stable shows nothing with dmesg, (other is OK).

Did you try "dmesg -a"?

The dmesg buffer is a circular buffer containing both
kernel output and console output.  However, "dmesg"
displays only the kernel output.  If there was lots of
console output, it filled all of the dmesg buffer,
so "dmesg" displays nothing (all of the kernel output
was overwritten by console output).  "dmesg -a" will
display everything, i.e. kernel + console output.

If "dmesg -a" doesn't print anything either, I'm afraid
I have no idea what might be wrong.  Well, you could try
"sysctl -b kern.msgbuf" which will retrieve the raw
contents of the dmesg buffer.

 >    - I tried loader.conf        kern.msgbuf=64000

I think it must be a multiple of the pages size, i,e,
4K = 4096 on FreeBSD/i386.  I usually set it to 65536
or 131072.

Best regards
   Oliver

-- 
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