hwclock on Virtual Machines has a different value than hwclock on the hypervisor

Solution Unverified - Updated -

Environment

  • Red Hat Enterprise Virtualization 3
  • Red Hat Enterprise Linux 5.8
  • VM is migrated from XEN

Issue

Hypervisors display correct time:

[root@hw ~]# hwclock --show
Fr 11 Okt 2013 14:16:09 CEST  -0.912115 Seconds
[root@hw ~]# date
Fr 11. Okt 14:16:08 CEST 2013

but the VMs that run on them display incorrect time:

[root@vm ~]# hwclock --show
Fr 11 Okt 2013 12:16:52 CEST  -0.781593 Seconds
[root@vm ~]# date
Fr 11. Okt 12:16:57 CEST 2013

Resolution

Set "UTC=true" in /etc/sysconfig/clock

Root Cause

Under XEN there is no "hwclock" and thus UTC setting has no effect. However after Virtual Machines are migrated to KVM / RHEV, the system clock gets set to wrong time via hwclock.

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