SnapOverflow

SnapOverflow Logo SnapOverflow Logo

SnapOverflow Navigation

  • Home
  • Server
  • Ubuntu

Mobile menu

Close
  • Home
  • System Administrators
    • Hot Questions
    • New Questions
    • Tags
  • Ubuntu
    • Hot Questions
    • New Questions
    • Tags
  • Help
Home / server / Questions

Questions[gps](server)

Martin Hope
Spencer
Asked: 2021-10-22 00:42:05 +0800 CST

Do NTP pool servers use gpsd?

  • 0

A bug in gpsd upon which some NTP servers rely, has been known for a couple of months, but it hasn't really become general knowledge until recently, just before the October 24, 2021 rollover that may set some NTP servers' clocks back to 2002. A patch for GPSD fixes the bug.

Since my company doesn't have high time synchronization needs with the outside world, we use the NTP pool servers as our ultimate source of accurate time. (Everything in the network synchronizes with a single device in the network, which synchronizes with the pool servers.)

The NTP pool website doesn't have any news after 2019, but interestingly, one of those items is about another GPSD week rollover that happened in 2019.

Various institutions belong to the NTP server pool on a voluntary basis, and so they're each going to have their own means of getting accurate time.

Is it known whether any of these servers use gpsd?

This other Server Fault question doesn't address the issue, but it does give an example of why the problem might be so complicated.

service ntp gps
  • 1 Answers
  • 195 Views
Martin Hope
Palace Chan
Asked: 2016-11-16 21:26:00 +0800 CST

Is PTP really more precise than NTP? If so, why?

  • 4

I have read quite a bit about NTP and PTP time keeping protocols. While many sources claim that PTP is more precise than NTP for that type of granularity - the reason is not as clear. Why can't NTP be just as accurate if a stratum 0 reference clock is atomic from GPS and network delays are accounted for? A paper on the FSMLabs site, in fact, claims that if both protocols are implemented well (as in TimeKeepeer they say), they can both deliver similar precision - and that it really boils down to the ability to stamp time in hardware to better account for jitter in switches, routers, and operating systems.

time ntp ptp gps
  • 1 Answers
  • 810 Views
Martin Hope
NPE
Asked: 2010-09-25 01:34:22 +0800 CST

Seemingly poor quality of NTP time synchronization using a GPS clock

  • 7

I have a Linux server which has its time synchronized to a GPS-based NTP appliance located close by. Ping times from the server to the appliance are circa 1ms, with very low jitter:

--- x.x.x.x ping statistics ---
100 packets transmitted, 100 received, 0% packet loss, time 99001ms
rtt min/avg/max/mdev = 0.874/0.957/1.052/0.051 ms

However, the NTP client estimates the accuracy of time synchronization to be around 5-6ms, which seems very high given the setup:

synchronised to NTP server (x.x.x.x) at stratum 2
   time correct to within 5 ms
   polling server every 16 s

ntpq -p gives the following:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*x.x.x.x         .PPS.            1 u   10   16  377    0.964   -0.019   0.036

Two questions:

  1. What may be causing the NTP client to have such low confidence in the accuracy of the synchronization?
  2. Is there any way to measure the actual accuracy of the synchronization, say to the nearest millisecond?
linux ntp gps
  • 3 Answers
  • 10853 Views
Martin Hope
2 revsuser640
Asked: 2009-06-19 11:46:32 +0800 CST

Is anyone using GPS for time sync?

  • 37

I've come across a handful of GPS NTP servers, as well as some inexpensive solutions using off-the-shelf receivers and software. Right now I'm just using NTP with a list of servers over the Internet. What is the advantage to using GPS instead (considering the alternative is free)?

ntp time-synchronization gps
  • 12 Answers
  • 20961 Views

Sidebar

Stats

  • Questions 681965
  • Answers 980273
  • Best Answers 280204
  • Users 287326
  • Popular
  • Answers
  • Marko Smith

    Can you pass user/pass for HTTP Basic Authentication in URL parameters?

    • 5 Answers
  • Marko Smith

    Ping a Specific Port

    • 18 Answers
  • Marko Smith

    Check if port is open or closed on a Linux server?

    • 7 Answers
  • Marko Smith

    How to automate SSH login with password?

    • 10 Answers
  • Marko Smith

    How do I tell Git for Windows where to find my private RSA key?

    • 30 Answers
  • Marko Smith

    What's the default superuser username/password for postgres after a new install?

    • 5 Answers
  • Marko Smith

    What port does SFTP use?

    • 6 Answers
  • Marko Smith

    Command line to list users in a Windows Active Directory group?

    • 9 Answers
  • Marko Smith

    What is a Pem file and how does it differ from other OpenSSL Generated Key File Formats?

    • 3 Answers
  • Marko Smith

    How to determine if a bash variable is empty?

    • 15 Answers
  • Martin Hope
    Davie Ping a Specific Port 2009-10-09 01:57:50 +0800 CST
  • Martin Hope
    Smudge Our security auditor is an idiot. How do I give him the information he wants? 2011-07-23 14:44:34 +0800 CST
  • Martin Hope
    kernel Can scp copy directories recursively? 2011-04-29 20:24:45 +0800 CST
  • Martin Hope
    Robert ssh returns "Bad owner or permissions on ~/.ssh/config" 2011-03-30 10:15:48 +0800 CST
  • Martin Hope
    Eonil How to automate SSH login with password? 2011-03-02 03:07:12 +0800 CST
  • Martin Hope
    gunwin How do I deal with a compromised server? 2011-01-03 13:31:27 +0800 CST
  • Martin Hope
    Tom Feiner How can I sort du -h output by size 2009-02-26 05:42:42 +0800 CST
  • Martin Hope
    Noah Goodrich What is a Pem file and how does it differ from other OpenSSL Generated Key File Formats? 2009-05-19 18:24:42 +0800 CST
  • Martin Hope
    Brent How to determine if a bash variable is empty? 2009-05-13 09:54:48 +0800 CST
  • Martin Hope
    cletus How do you find what process is holding a file open in Windows? 2009-05-01 16:47:16 +0800 CST

Related Questions

Trending Tags

linux nginx windows networking ubuntu domain-name-system amazon-web-services active-directory apache-2.4 ssh

Explore

  • Home
  • Questions
    • Hot Questions
    • New Questions
  • Tags
  • Help

Footer

SnapOverflow

About Us

  • About Us
  • Contact Us

Legal Stuff

  • Privacy Policy

Help

© 2022 SOF-TR. All Rights Reserve