[ntp:questions] running NTP as server only
folkert at vanheusden.com
Thu Aug 19 15:41:59 UTC 2010
> >> uh, to quote Landauer, all information is physical. All virtual
> >> machines MUST also run on physical machines.
> > But that does not mean you can run NTP on them.
> > E.g. on VMware ESX, you cannot do this.
> > (there is an NTP running on the console session, but that is just a
> > virtual machine running a Linux variant, it is not running on the
> > physical machine either)
> And not so long ago, somebody quoted a more recent whitepaper here
> that said running NTP in the virtual machines was now working much
> better and in fact recommended.
Using NTP in Linux and Other Guests
The Network Time Protocol is usable in a virtual machine with proper
configuration of the NTP daemon. The
following points are important:
Do not configure the virtual machine to synchronize to its own
(virtual) hardware clock, not even as a
fallback with a high stratum number. Some sample ntpd.conf files
contain a section specifying the local
clock as a potential time server, often marked with the comment
âundisciplined local clock.â Delete any
such server specification from your ntpd.conf file.
Include the option tinker panic 0 at the top of your ntp.conf
file. By default, the NTP daemon
sometimes panics and exits if the underlying clock appears to be
behaving erratically. This option causes
the daemon to keep running instead of panicking.
Follow standard best practices for NTP: Choose a set of servers
to synchronize to that have accurate time
and adequate redundancy. If you have many virtual or physical
client machines to synchronize, set up
some internal servers for them to use, so that all your clients
are not directly accessing an external
lowâstratum NTP server and overloading it with requests.
(vmware document of 2008, status of vmware 3.5)
> In situations where the host has enough cores that they can be
> allocated more persistently to running VMs, I can even see this work.
> The problem used to be, mostly, that interrupts didn't (always) arrive
> on time. Yet another problem solved by throwing hardware, to wit
> interrupt lines, at it.
Folkert van Heusden
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