Jason Pyeron wrote: > > >> -----Original Message----- >> From: centos-bounces at centos.org >> [mailto:centos-bounces at centos.org] On Behalf Of Warren Young >> Sent: Thursday, August 12, 2010 17:41 >> To: CentOS mailing list >> Subject: Re: [CentOS] Date drift and ntpd >> >> 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 192.168.1.65 >> Some 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. > > Okay, I only have one timeserver, but the ntp clients cowardly refuse to use > less than 3. Back to the man page... One server should be fine - you must have something else wrong, like your authoritative server not being a low stratum number - or not convinced itself that its time is correct. -- Les Mikesell lesmikesell at gmail.com