On 10/28/2012 10:16 PM, Tristan Seligmann wrote: > On Mon, Oct 29, 2012 at 12:05 AM, Phil Mayers <p.may...@imperial.ac.uk> wrote: >> This depends on how you're running ntpd. If you have "-x" on the command >> line, yes - ntpd will not step. >> >> If not, there are circumstances it will step - clock diffs in excess of >> 128ms iirc? > > If an offset of 128ms occurs at any time other than initial ntpd > startup (which will presumably occur at system startup), that means > you've either experienced a significant period of time without > connectivity to time servers[1], you have a hardware / kernel issue > that should be resolved, or some other software on the system is > messing with the clock. Aside from network issues, the other > possibilities are all serious issues that should be corrected, not > tolerated as a normal situation.
Sadly, this is not the case. As has already been pointed out, virtual machine clocks can undergo stepping in "normal" oepration. A specfic example: if a VMWare installation performs live migration of a host. We often see: ntpd[1793]: time reset +0.263757 s ...when this happens. This can occur several times a day, as we're running vCenter-controlled auto-migration - a very common setup. This is forward stepping of course, so is relatively harmless (backward is a pain). > >> Who knows what newer implementations like chrony or openntpd do! > > If they're doing something silly, then maybe you shouldn't use them. I have no reason to suspect they are doing somthing silly. I merely point out that there are other implmentations than the common ntpd, and that I don't know if they step or not. In fact, a little research suggests that chrony has *better* behaviour w.r.t stepping than ntpd: http://lists.fedoraproject.org/pipermail/devel/2010-May/135679.html ...which is nice. I sense a bit of defensiveness to this reply, TBH. Maybe I'm imagniing it, but if so that's unncessary. I don't hold a strong position about Twisted having a monotonic clock. When the original ticket was discussed here months ago, I was quite alarmed because the symptoms sounded dire. Further discussion clarified what the issues were, and I decided they weren't significant (for us). Maybe "Twisted doesn't need a monotonic clock" is the right reply, but it would be wrong to base that on the assumpton that "ntpd doesn't step" - that's all I was trying to say. Cheers, Phil _______________________________________________ Twisted-Python mailing list Twisted-Python@twistedmatrix.com http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
