XEN VM's unable to synchronise time with NTP on RHEL5.4
Environment
- Red Hat Enterprise Linux 5.4
- Host: Dell R710
Dual Processor, quad core
72Gb memory
Linux <example.com> 2.6.18-164.el5xen #1 SMP Tue Aug 18 15:59:52 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux
- Client: VM
Linux <example.com> 2.6.18-164.15.1.el5 #1 SMP Mon Mar 1 10:56:08 EST 2010 x86_64 x86_64 x86_64 GNU/Linux
Issue
- XEN VM's unable to synchronise time with NTP on RHEL5.4
Resolution
For RHEL5.4 the parameter below needs to be added to the kernel line on grub.conf
divider=10 notsc lpj=n
| Red Hat Enterprise Linux | Additional guest kernel parameters |
|---|---|
| 5.4 AMD64/Intel 64 with the para-virtualized clock | Additional parameters are not required |
| 5.4 AMD64/Intel 64 without the para-virtualized clock | divider=10 notsc lpj=n |
| 5.4 x86 with the para-virtualized clock | Additional parameters are not required |
| 5.4 x86 without the para-virtualized clock | divider=10 clocksource=acpi_pm lpj=n |
| 5.3 AMD64/Intel 64 | divider=10 notsc |
| 5.3 x86 | divider=10 clocksource=acpi_pm |
| 4.8 AMD64/Intel 64 | notsc divider=10 |
| 4.8 x86 | clock=pmtmr divider=10 |
| 3.9 AMD64/Intel 64 | Additional parameters are not required |
| 3.9 x86 | Additional parameters are not required |
Referenced on: This content is not included.This content is not included.http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Virtualization/chap-Virtualization-KVM_guest_timing_management.html
Root Cause
The clock tick speed in a virtual machine can run at a different frequency to what the kernel expects hardware to be running at. The system expects more ticks than are provided by the hypervisor, and runs roughly ten seconds worth of ticks in one second.
Diagnostic Steps
From Host:
# uname -r
# Linux <example.com> 2.6.18-164.el5xen #1 SMP Tue Aug 18 15:59:52 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux
# cat /boot/grub/grub.conf
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