Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have noticed that when I start ntpd on a server, checks against that server reveal that it has a stratum of zero. If I understand this correctly, I believe this means that ntpd is currently only using itself as the time source.

After a minute or so, it checks against the server, and the stratum is no longer zero.

Do I understand this correctly, and can I speed up time the time before it becomes non-zero?

share|improve this question
In your ntp configuration, there should be a "local clock" reference. What is the stratum listed there? – Matt Simmons May 6 '11 at 13:12
That isn't in the ubuntu server default configs. – Kyle Brandt May 6 '11 at 13:17
Interesting. The CentOS/RHEL config has two servers configured with "server 127.1271.0 stratum 10". Looking at that again, I'm pretty sure it doesn't change the behavior you're talking about. – Matt Simmons May 6 '11 at 13:27
OK, mine defaults to stratum 16 when it's in the initial startup. What ntp server are you running? – Matt Simmons May 6 '11 at 13:38
Guys, clearly the part that Kyle left out is that he's got his server hooked up to a TARDIS. – Phil Hollenback May 6 '11 at 15:22
up vote 2 down vote accepted

This sounds like a bug (or a configuration edit gone horribly wrong) - As Matt Simmons pointed out ntpd usually defaults to Stratum 16 ("Unsynchronized").

My (admittedly limited) understanding of NTP strata is that Stratum 0 is reserved for reference clocks (a cesium clock for example, or a GPS Time receiver) that you would attach to a computer to create a stratum 1 server (using the stratum 0 device as its reference).

share|improve this answer
Hmm... could be the Nagios check_ntp_time gone wrong as well.... – Kyle Brandt May 6 '11 at 15:31
Could be - I'm not sure how good the Nagios NTP stuff is. What does ntpq -c readlist show as the stratum? – voretaq7 May 6 '11 at 15:38
@vortaq7: It shows 16, so apparently it is this program being silly. – Kyle Brandt May 6 '11 at 20:28

Local clock should not be used.

you can speed up synchronization by using the iburst keyword for your server definitions.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.