[CentOS] system time automatically fowards in time and then comes back to normal

nate centos at linuxpowered.net
Sun Nov 22 15:08:13 UTC 2009


ankush grover wrote:

> Earlier this server was syncing time through ntp daemon and below is
> the ntp.conf file. Now I have set a cronjob which sync the time with

Best not to run NTP inside a ESX VM. I've never gotten NTP to sync
inside of VMware outside of a kernel with VMI enabled (no versions
of RHEL support VMI at this time as far as I know).

What I do for my ~40 ESX/ESXi hosts:
- Have your ESX hosts sync to a good NTP server
- Make sure vmware tools is installed and running correctly
  (/etc/init.d/vmware-tools status)
- Enable time sync for your guest, either via the UI or via
  this command in the guest(I have this command run in cron
  every 5 minutes as I have seen for some reason time sync turn
  itself off:
   /usr/sbin/vmware-guestd --cmd "vmx.set_option synctime 0 1"
- On top of all of that I have another cron set to run ntpdate
  every 5 minutes against a local NTP server:
   /usr/sbin/ntpdate `cat /etc/ntp/step-tickers | grep -v \#`

For providing NTP services themselves, currently I run 3 VMs
at each site with Fedora 8 with VMI enabled for the guest VM
(the kernel in FC8 supports VMI, I suspect newer Fedoras work
fine too I just have no reason to change right now). And I have
these FC8 VMs sync to internet hosts(mainly time.nist.gov) so
my internal ESX and other systems can sync against them(they
are load balanced behind a F5 BigIP).

from FC8 kernel log:
VMI: Found VMware, Inc. Hypervisor OPROM, API version 3.0, ROM version 1.0
vmi: registering clock event vmi-timer. mult=9483317 shift=22
Booting paravirtualized kernel on vmi
vmi: registering clock source khz=2260999
Time: vmi-timer clocksource has been installed.

I currently run roughly 400 VMs this way and don't have any
noticeable time-related issues.

nate



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