We have a local time server and all of our machines are pointed at it for the time. How can the clock drift by a day and a half? [root at devserver21 ~]# date Fri Aug 13 14:43:29 EDT 2010 [root at devserver21 ~]# rdate -s 192.168.1.67 [root at devserver21 ~]# date Thu Aug 12 07:02:39 EDT 2010 [root at devserver21 ~]# cat /etc/ntp.conf | grep -v ^# | grep -v ^$ restrict default nomodify notrap noquery restrict 127.0.0.1 server 192.168.1.67 server 192.168.1.66 server 192.168.1.65 server 127.127.1.0 # local clock fudge 127.127.1.0 stratum 10 driftfile /var/lib/ntp/drift broadcastdelay 0.008 keys /etc/ntp/keys -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- - - - Jason Pyeron PD Inc. http://www.pdinc.us - - Principal Consultant 10 West 24th Street #100 - - +1 (443) 269-1555 x333 Baltimore, Maryland 21218 - - - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- This message is copyright PD Inc, subject to license 20080407P00.
Jason Pyeron sent a missive on?2010-08-12:> We have a local time server and all of our machines are pointed at it > for the time. > > How can the clock drift by a day and a half? > > [root at devserver21 ~]# date > Fri Aug 13 14:43:29 EDT 2010 > [root at devserver21 ~]# rdate -s 192.168.1.67 > [root at devserver21 ~]# date > Thu Aug 12 07:02:39 EDT 2010 > [root at devserver21 ~]# cat /etc/ntp.conf | grep -v ^# | grep -v ^$ > restrict default nomodify notrap noquery restrict 127.0.0.1 server > 192.168.1.67 server 192.168.1.66 server 192.168.1.65 > server 127.127.1.0 # local clock > fudge 127.127.1.0 stratum 10 > driftfile /var/lib/ntp/drift > broadcastdelay 0.008 > keys /etc/ntp/keys > >Hi, It is unlikely that the machine in question drifted forward in time if ntpd was running. Have a look at the logs /var/log/messages it should contain the ntpd log messages which will help you determine what happened to the time. Also check that ntpd is running with: "service ntpd status" and also "chkconfig ntpd --list" will show the startup position of ntpd HTH Simon.
On 8/12/2010 5:07 AM, Jason Pyeron wrote:> > [root at devserver21 ~]# cat /etc/ntp.conf | grep -v ^# | grep -v ^$ > restrict default nomodify notrap noquery > restrict 127.0.0.1 > server 192.168.1.67 > server 192.168.1.66 > server 192.168.1.65Some HOWTOs tell you that more time servers is better, on a standard knee-jerk redundancy theory, but they're ignoring two things. First, you already have a fallback: the system's built-in clock. It's perfectly fine to run on that while you ride out your time server's downtime. Second, ntpd, internally, is built on a phase-locked loop, which is supposed to stabilize its time corrections in the face of jitter and other bad things out in the real world. Like anything based on a negative feedback loop, however, it can be destablized with certain inputs. Giving ntpd two or more servers is a pretty good way to destabilize its PLL in the real, non-ideal world we find on the modern Internet. To anyone considering flaming me, please read this first: http://queue.acm.org/detail.cfm?id=1773943 At minimum, read the section "One server is enough". The bit on PLLs about halfway down is also directly relevant.