dmesg not working on new system

Greg Barniskis nalists at
Mon Jun 5 12:23:46 PDT 2006

Lowell Gilbert wrote:
> Greg Barniskis <nalists at> writes:
>> Chris Maness wrote:
>>> On Mon, 5 Jun 2006, Greg Barniskis wrote:
>>>> Chris Maness wrote:
>>>>> I just installed 6.1 and upgraded to RELEASE-p1.  The command
>>>>> dmesg is not displaying any kernel messages, any suggestions? 
>>>> Suggests all is well?
>>>> dmesg outputs stuff from the current system message buffer, which
>>>> contains your boot messages right after booting but those can get
>>>> flushed over time. Boot messages are saved to a file though, for
>>>> reference.
>>>> more /var/run/dmesg.boot
>>> I just thought it was strange because every other system I have it
>>> at least displays dmesg.boot if there is no other messages.  Is this
>>> new behavior for 6.1?
>> Not new behavior. A dmesg on any of my running systems (4.x, 5.x)
>> returns nothing after a time. You were just catching it before the
>> buffer was flushed. I don't know what triggers that, and it is
>> possible that the trigger/timing of it may have changed in 6.x (and as
>> always, YMMV).
> Interesting.  Does "dmesg -a" show anything different?

Sure. On a mail server, -a reveals tons of SMTP timed out messages 
(primarily spammers who cut and run when 550'd). On a firewall, -a 
shows tons of ipfw log messages. On a web server, -a shows mainly 
ssh login (and su) success/failure.

Chris Howells wrote:
> dmesg is not flushed here.

Hmmm.... interesting. It has always eventually flushed around here, 
which prompted me to read the dmesg man page, which pointed me at 

I never really thought about it much after that, and really still 
don't think it too odd... but if anyone thinks the behavior is 
erratic and in need of troubleshooting, I'll try to answer any other 
questions about my setup.

But I don't see anywhere that the man page says "dmesg will always 
report the boot messages no matter what". It says it reads the 
system message buffer, and when something is a buffer I immediately 
think of it as a temporary thing. YMMV, obviously.

Greg Barniskis, Computer Systems Integrator
South Central Library System (SCLS)
Library Interchange Network (LINK)
<gregb at>, (608) 266-6348

More information about the freebsd-questions mailing list