Michael Colvin wrote:
Is anyone running the QMT iso on a VMWare VM? I had one set up just to play
with, but noticed the clock keeps horrible time. I was able to adjust the
"ticks" to keep it more accurate, along with an hourly sync, but this seems
ridiculous. From what I've found, it's an issue with CentOS in a VM, but
I've got CentOS running in a VM for a PBX, and it seems fine.
This is the only time I've ever had an issue with the system/hardware clock
drifting dramatically in a VM. There are also other VM's on this physical
server that keep sync fine...
For a few years I've been running a few in VMware Server on top of
Centos 5. I'm currently running them in VMware Server 2 on CentOS 5.2
64-bit.
I saw timekeeping issues initially and did some research. I found a
VMware whitepaper: http://www.vmware.com/pdf/vmware_timekeeping.pdf.
I've attached my notes from studying that whitepaper.
Basically you need to not use NTP or other native timekeeping tools in
the guest OS, rather install VMware tools and set them to sync the guest
with the host.
Brent Gardner
Time issues in VMWare guests
Refer to http://www.vmware.com/pdf/vmware_timekeeping.pdf
Guest machines may have issues keeping correct time.
Guidelines:
- Do not overload the host machine.
If it is too busy, guest machines will not get enough host CPU time to keep
themselves up to date.
- Make sure CPU throttling and/or power management is disabled in BIOS or
turned off in the OS on the host.
Guest timekeeping depends a lot on the host CPU.
- Do not run non-VMWare timekeeping tools on guest machines:
- no NTP on Unix-like guests.
- disable Windows Time service on Windows guests.
- Install VMWare Tools and configure for time sync.
VMWare tools are meant to be configured with a GUI tool in the guest OS.
For guests that do not support a GUI environment, the relevant setting can be
set in the guest's vmx file:
tools.syncTime = "TRUE"
- Properly configure non-VMWare timekeeping tools such NTP or Windows Time
service on the host machine.
Linux guests with 2.6 kernels should have the following kernel option set:
clock=pit
- or -
clocksource=pit
Here's an example /etc/grub.conf from a CentOS 5 guest machine:
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.18-8.1.8.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-8.1.8.el5 ro root=/dev/VolGroup00/LogVol00
clocksource=pit
initrd /initrd-2.6.18-8.1.8.el5.img
title CentOS (2.6.18-8.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-8.el5 ro root=/dev/VolGroup00/LogVol00
initrd /initrd-2.6.18-8.el5.img
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