Integrity VM - It is possible for a VM Guest to run with time different to it's VM Host?

[Pete Des Moulins]

Bit of a strange situation that I have to explore guru's - so please bear with me...

I need to determine whether I can configure a VM Guest to run with it's O/S clock time totally separate from it's VM Host server (and hardware clock) time and from any other guests on that host.

This is to enable the one specific VM Guest to perform Application testing simulating 'End-Of-Period/Year' processing.
Therefore, I am not just talking shifting timezones, I am talking timeshifts of months/years.


Reason: I have been asked to confirm that an App running on a VM Guest will be able to run in this manner by manipulation of the HP-UX Operating System time.


Some simple testing that I have done has already shown the following:

1) A VM Guest system CAN run it's O/S time (as indicated by the 'date' command) separate from it's VM Host, as well as separate from several other guests located on the same host.
( In my case, the matter happened as a result of one guest not time sync'ing via NTP)

2) A reboot of the VM Guest in question does not result in it re-synching with the host system.
[ This was good from my perspective, but I'd like to understand the underlying mechanism that enables the VM Guest to boot and maintain the previous offset from the host system].

[unixdaddy · Accepted solution]

I would say yes. I have a test environment and i tested your situation. Please note this is with a 11.31 host running HPVM 4.0

1. first verify/alter date/time on vmguest

# uname -a
HP-UX virtual1 B.11.31 U ia64 0851789234 unlimited-user license
# date
Wed Mar 25 14:34:28 GMT 2009
# date 032515002025
Tue Mar 25 15:00:00 GMT 2025
# date
Tue Mar 25 15:00:03 GMT 2025

2. verify time is different on vmhost

# uname -a
HP-UX vmhost1 B.11.31 U ia64 1897976890 unlimited-user license
# date
Wed Mar 25 14:37:45 GMT 2009

3. reboot vmguest and verify time remains
VMGUEST
# shutdown -r -y 0

SHUTDOWN PROGRAM
03/25/25 15:02:24 GMT
.....

Closing open logical volumes...
Done


*** VM restarting ***

# uname -a
HP-UX virtual1 B.11.31 U ia64 0851789234 unlimited-user license
# date
Tue Mar 25 15:09:03 GMT 2025

4. confirm time on vmhost remains the same
# uname -a
HP-UX vmhost1 B.11.31 U ia64 1897976890 unlimited-user license
# date
Wed Mar 25 14:46:30 GMT 2009

[Richard Hepworth]

I have just finished very similar testing with no issues. (VM 4.0 on 11.31 host).

Just remember to stop xntpd on your guest :-)

[Rita C Workman]

Remember, a virtual machine, for virtually (no pun intended) all intents and purposes, is it's own operating system. Hence how you set the time on that VM Guest is how it operates. It shouldn't matter what the VM Host is doing for time - they are two separate operating systems.


If you had a sync'ing problem via NTP then you might need to check your configuration on the node.

Regards,
Rita