[ntp:questions] System Time (date) Versus Hardware Clock Time (hwclock)

Gordon Dickens gordon at dickens.com
Sun Jul 22 10:44:31 UTC 2007


I am new to both ntp and this list. I recently configured and began 
using npt on my Linux server. I am running CentOS release 4.5 version 
2.6.9-55.0.2.ELsmp and npt version 4.1.1b-r5 which was preloaded with my 
CentOS Linux distribution.

I am having a problem with my system time, reported via the "date" 
command in that it doesn't agree with the hardware clock time, reported 
via the hwclock command. The "date" command reports time that is always 
23 seconds behind the time reported by the "hwclock --show" command.  It 
appears that the time reported by "hwclock" is accurate in that it 
agrees with other ntp servers that I query.  Whereas, it appears that 
the time reported by "date" is inaccurately slow by 23 seconds.

As an example, at the exact moment when other ntp servers report the 
time as 11:00:00 AM EDT then I get the following results from this 
nested Linux shell command line:

# date;/sbin/hwclock --show
Fri Jul 20 11:59:37 EDT 2007
Fri 20 Jul 2007 11:00:00 AM EDT  -0.015949 seconds

Can anybody tell me how to make "date" time accurately equal "hwclock" time?

FWIW, when I set the two times to be equal and accurate with other ntp 
servers with "hwclock --hctosys" then the following occurs:

- Both "date" and "hwclock" will remain correctly in agreement with 
other ntp servers for several minutes.
- Then, the jitter values for the servers with which I am syncing go up 
to around 8700 (my jitter values are normally less than 10).
- Then the ntpd daemon quits syncing (no asterisk "*" next to any 
server) and the jitter values go to around 18000.
- After which the offsets go to 23000 milliseconds (my offset values are 
normally under 100 milliseconds) although both the "date" and "hwclock" 
command continue to agree with other ntp servers.
- Following all this, and after about 15 minutes, everything goes back 
to how it was in the beginning with the "date" time trailing the 
"hwclock" time and other ntp servers by about 23 seconds and with 
offsets under 100ms and jitter less than 20.

In any event, I hope that someone can offer some advice as to how to fix 
my clocks so that "date" = "hwclock" which agree with other ntp clocks 
within a reasonable amount of accuracy.

Thanks in advance for your help!


More information about the questions mailing list