[asterisk-users] kernel: dahdi: Detected time shift.

[Shaun Ruffell]

On 11/24/2010 10:43 AM, Jonas Kellens wrote:
> Hello list,
> 
> I'm experiencing a lot of server freezes lately. The server just... freezes.
> 
> I notice in the log files (/var/log/asterisk/messages &
> /var/log/messages) that logging stops at the time the server hangs.
> Logging continues when the server has been restarted (which is the only
> solution).
> 
> So it is not a proces that hangs, it's the entire server (CentOS5.5 +
> Asterisk + MySQL).
> 
> I really have no idea what can be causing these sudden freezes. Memory
> stays mostly at 250MB of 512 MB total, CPU is 97% to 100% idle...
> 
> /var/log/asterisk/debug tells me nothing, no lines that indicate
> something strange before the freeze (debug level 9).
> 
> I have no core.pid file in /tmp, when I look after rebooting the server.
> 
> The only thing I have is a high level of mentionning of "kernel: dahdi:
> Detected time shift." in /var/log/messages.
> 
> 
> What is causing this kernel message ? Could this be the cause of the
> server freeze ?
> 

When a system does not have a hardware device installed DAHDI uses the
system time in order to approximate a telephony clock source (what was
previously referred to as dahdi_dummy).  Since it uses the system time
to accomplish this, if there is a large gap in the time (typically
because NTP is adjusting the time) DAHDI just reports that it thinks
it's very far behind or ahead of where it should be, and doesn't even
try to "mix" any audio for that interval.

So, I think the "detected time shift" is more a symptom of something
else causing locks as opposed to the source.

Is your server keeping accurate wall-time?

-- 
Shaun Ruffell
Digium, Inc. | Linux Kernel Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at: www.digium.com & www.asterisk.org