[ntp:questions] no drift-file on 2008 R2 vps and the time diff. is getting bigger and bigger?

Martin Burnicki martin.burnicki at meinberg.de
Mon Sep 15 09:02:25 UTC 2014


gooly wrote:
> Hi,
> I just installed ntp (Meinberg, once on Win7, once on a vps 2008 R2).

Please note this is the standard NTP software from ntp.org. We at 
Meinberg just build the binaries from the public sources and put them 
into a setup program to simplify installation on windows.

> On my Win 7 I see in C:\Program Files (x86)\NTP\etc the drift file
> but on the vps there is no drift-file?
> And after starting (and several restarts) the time-difference getting
> bigger and bigger.
> What's going wrong?

There are 2 basic problems here:

1.) Ntpd expects the system time to increase monotonically, and at a 
constant rate. It can then try to determine the system time drift 
compensate it, and save the determined value in the drift file.

Virtual machines may not keep time properly at all, depending on how the 
virtualization software has been implemented. E.g. in early versions of 
VMware timekeeping was very unstable, so you couldn't use ntpd 
successfully at all. However, in current VMware versions this has been 
very much improved, so ntpd works  as expected.

If subsequent pollings of real NTP servers from within a VM may don't 
yield consistent results then ntpd is unable to determine the real 
drift, and compensate it, and thus no drift file is created.

2.) In an earlier reply from September 3
I've pointed you to some information *why* and *how* you should upgrade 
to a newer NTP version

Ntpd v4.2.6p5 (the current stable version) *may* work properly on 
Windows Vista and newer, but there's a good chance that it is unable to 
discipline the Windows system time even on a physical machine, and due 
to limitations of virtualization things even get worse in a VM.

So I suggest you

- try with updated binaries
- use minpoll 6 maxpoll 6 when specifying your time servers

When ntpd starts it tries to get the required rights to set the system 
time, and if Windows doesn't grant these rights there should be an 
associated entry in the Windows application event log.

However, I doubt that your problems are due to limited rights.

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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