I want to setup an SNTP server for testing purposes that

  1. can be set to any arbitrary value (for example testing DST behaviour of the device under test)
  2. serve only on eth1 on my RedHat Enterprise box. I want to limit it into a single interface (or network) so that it does not disrupt anything.

What is the easiest way to create such a setup? My must be always online on the other interface for e-mail etc. so I cannot set its time randomly.

  • @Chris S who deleted my answer, claiming it did not answer the question. I reread the question and as far as I can tell. it precisely answered the question. Again, AFAICT, the accepted answer below does not answer the question. Mar 20, 2014 at 20:35
  • @LostInTheTrees I agree that it was a valid answer. Mar 24, 2014 at 16:35
  • Thanks. Alas I know of no way to message Chris S. to get him to undo his damage. Mar 25, 2014 at 0:27

2 Answers 2


ntpdsim is what you want:

The ntpdsim program is an adaptation of the ntpd operating system daemon. The program operates as a discrete time simulator using specified systematic and random driving sources. It includes all the mitigation and discipline algorithms of the actual daemon, but with the packet I/O and system clock algorithms driven by simulation. Most functions of the real ntpd remain intact, including the monitoring, statistics recording, trace and host name resolution features. Further information on the simulator is on the NTP Discrete Event Simulator page.

The simulator is most useful to study NTP behavior in response to time and/or frequency transients under specific conditions of network jitter and oscillator wander. For this purpose the daemon can be driven by pseudorandom jitter and wander sample sequences characteristic of real networks and oscillators. The jitter generator produces samples from a Poisson distribution, while the wander generator produces samples from a Guassian distribution.



  • ntpdsim does not actually serve SNTP. As far as I can determine, both the servers and the client are simulated much faster than real time. If there is a configuration to get ntpdsim to serve large offsets without messing with a host's time, please post it. Jan 11, 2017 at 21:53

Why do you just want SNTP and not regular NTP? either way the best way is the usual 'ntpd', OpenNTP or 'clockspeed'.

  • +1 Have a look at the tinker command for ntpd to skew the clock, YMMV: eecis.udel.edu/~mills/ntp/html/miscopt.html#tinker
    – gravyface
    Feb 14, 2011 at 14:29
  • tinker is for adjusting a clock against ntp's better judgement. the OP wanted to test a server/client installation. ntpdsim does just that without mucking with the system clock
    – dfc
    Oct 25, 2011 at 20:15
  • OpenNTP and clockspeed actually set the system clock. he wants to test things. (you forgot chrony, another ntp server)
    – dfc
    Oct 25, 2011 at 20:16

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