Windows 7 time slowly changes
I have a 2012 domain with Windows 7 clients. Suddenly one client is having trouble syncing the time - at startup one day it was about 3 hours off. The timezone was set correctly. I've tried running "net time /RTSDOMAIN:domain /SET" and it syncs the client time to the PDC's time immediately, but after a while the clock starts to slow down again. Over the course of an hour it will get several minutes behind. This seems to be the only client with the issue. It's not a new client, has been running correctly for more than a year, and I'm unaware of any changes that could have caused this.
Is the windows client a VM?
ASKER
Yes.
You may be dealing with Vm time skew. Run this command: w32tm /query /source and let me know what you get back.
ASKER
That returns the name of the PDC.
Ok - assuming this DC is the Operations manager and therefor the authoritative Time source. Run the same query on the DC and let me know what you get.
ASKER
That returns 1.us.pool.ntp.org.
Ok so you are using NTP - good. What is your hypervisor?
ASKER
VMware.
Are the vmware host(s) configured for NTP?
Also is time sync configured for the vmware guest in question?
ASKER
This may be the issue...we just added a new (3rd) host and it looks like it is not configured for NTP. However, it seems odd that host 1 says "running" and lists the IPs of two DCs, but host 2 says the NTP client is "stopped" and still lists the IPs of two DCs. Then this new host 3 says "stopped" and doesn't list any IPs. I would think all 3 should be running? (It makes sense that the 3rd one hasn't yet been configured, but I am puzzled about why both of the original hosts aren't running)
ASKER
As far as time sync being configured for the guest, can you tell me where to check that?
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I think its still in Virtual Machine –> Edit Settings –> Options –> VMware Tools
ASKER
Ok, so I need to change the hosts to point to the same NTP server as the DC. And all 3 hosts should have NTP enabled?
Yes
ASKER
It looks like time sync is enabled...I guess I don't understand why this should be disabled?
3.3 Time SynchronizationSOURCE
Proper and accurate timekeeping is a critical service used by Active Directory and its clients for
authentication and replication arbitration. Due to the critical nature of having accurate time across
the environment, there is a perception that virtualization might exacerbate any flaws in the time
synchronization mechanisms used throughout the environment. Virtual machines are known to
experience some level of time drift due to the sharing of physical resources that can occur as a
result of multiple virtual machines running on a single physical host. This concern can be
mitigated by following VMware and Microsoft best practices for time keeping.
Operating systems track the passage of time using one of two methods: tick counting or tickless
timekeeping. In tick counting, the operating system uses a hardware device to pass interrupts at a
predetermined interval, such as 100 times per second. The operating system keeps track of these
interrupts, or ticks, to determine how much time has passed. In tickless timekeeping, a hardware
device keeps track of the number of time units that have passed since the system booted. When
needed, the operating system reads the counter. Windows-based operating systems use ticks to
keep time. Windows-based systems with multiprocessor HALs and some ACPI uniprocessor
HALs use the CMOS periodic timer to deliver interrupts, or ticks.
In addition to tracking the passage of time, operating systems must keep track of absolute time,
or wall-clock time. During startup, the operating system reads wall-clock time from the CMOS, to
the nearest second, or from a network time source. In virtual machines, VMware Tools™ provides
an additional mechanism to synchronize the guest operating system’s clock with the host’s clock.
© 2014 VMware, Inc. All rights reserved.
Page 11 of 62
Virtualizing Active Directory Domain Services on VMware vSphere
Timer devices in physical machines tend to drift as do those in virtual machines. As a result,
timekeeping software is generally required to keep time accurate over the long term. For
Windows-based operating systems, this is provided natively using the Windows Time Service
(W32Time).
In an Active Directory forest, the Windows Time Service keeps time following a hierarchy, starting
at the forest root PDC emulator to the lowest-level domain clients. Because of Active Directory’s
dependence on the Windows Time Service, it is the natural choice for time-keeping within
Windows-based guests.
By default, domain-joined Windows systems use the domain hierarchy for time keeping. In virtual
machines, this setup might conflict with VMware Tools periodic clock synchronization. The result
is two time services, one pointing to a reliable time source, the other pointing to a non-reliable
time source, thereby updating the time to inaccurate values. For this reason, the recommendation
is to standardize on one tool. For domain-joined Windows machines, the Windows Time Service
is the preferred method.
VMware Tools time synchronization is disabled by default. To verify that time synchronization is
disabled, check the VMware Tools user interface or virtual machine advanced configuration
(.vmx file). Even with VMware Tools time synchronization disabled, time synchronization is
performed during guest operating system startup and during some virtual machine maintenance
operations on the vSphere platform.
For more information on disabling VMware time synchronization for virtual machines, see the
VMware KB article Disabling Time Synchronization at http://kb.vmware.com/kb/1189.
ASKER
Ok thank you. I'll make the changes and let you know how it goes.
fallriverelectric--
Install a new CMOS battery
Install a new CMOS battery
ASKER
That worked great. Thanks for the help!