The Futility of Changing the System Time in the Virtual Machine Bios

The Futility of Changing the System Time in the Virtual Machine Bios

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You may or may not be aware that when you are booting a virtual machine under Virtual PC or Virtual Server you can press the Del key to enter the virtual machines bios.  The first configurable option that you'll see in the bios is the System Time and System Date.  You can easily change these values, however there is no point.  You see, the virtual machine will be rebooted after any Bios changes are made (this is standard behavior for computers) and when the virtual machine reboots its system time and date will be automatically reset to match those of the host operating system.

Cheers,
Ben

P.S.  Occasionally we get requests cannot override the system time when the virtual machine is rebooted.  But the reality is that the host operating system time is the most accurate value that we have to use for the virtual machine time when booting the virtual machine.

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  • But what if I don't want the time in the virtual machine to be accurate?

    We recently wanted to replicate the behaviour of a machine with a busted CMOS battery, which caused the clock to be set back to 1980-ish. Shortly after booting, the clock would be sync'ed to the DC, jumping forward by about 25 years.

    It would have been nice to be able to have replicated this with a virtual machine.

  • You might add a new configuration setting and allow a user to set up some time difference (which would default to 0) between host OS and that running inside VM.

    This would be very helpful.

  • I use Virtual Server 2005 R2.  When I configure a virtual machine with the additions installed, I can click on the "Virtual Machine Additions" link to get the VM Additions configuration page.  On this page, under the section "Additions features" there is a checkbox named "Host time synchronization."  What is the purpose of this checkbox if not to enable and disable the virtual machine from automatically syncing time with the host machine?

    As Roger points out, there are legitimate scenarios for wanting to test machines with a time different from that of the host machine.

  • Of course, even if you agree with the behaviour, it begs the question - why allow the option of changing the time in the BIOS if it cannot have any effect?

  • Brad: I think this controls periodic syncing of time, not just on boot.

    Brent: I assume because the BIOS image is taken from a REAL BIOS, which has this feature?

  • Roger / Robert -

    We have heard this before.  The problem is that if we did this it would be too easy to abuse and use for piracy purposes.  If you need a short term test you can change the time on the host operating system.

    Brad -

    The time synchronization option that you can enable or disable under Virtual Server is the periodic time syncing done by the Virtual Machine Additions (every 15 seconds) while the virtual machine is running.

    Brent -

    Yeah - we did not catch this one :-)

    We actually scrubbed the BIOS to remove a lot of pointless options - but the reality is that most of the stuff that we left behind is not that usefull either.

    Cheers,

    Ben

  • > You see, the virtual machine will be rebooted

    > after any Bios changes are made (this is

    > standard behavior for computers)

    It is standard behaviour for computer BIOSes to demand reboots after SOME kinds of configuration changes but not after trivial things like changing the date and time.  Changes to the date and time are applied immediately without waiting for an "OK" click, sort of like the way Windows used to immediately apply users' adjustments to date and time without waiting for an "OK" click.

    Tuesday, November 28, 2006 4:39 AM by Roger Lipscombe

    > We recently wanted to replicate the behaviour

    > of a machine with a busted CMOS battery, which

    > caused the clock to be set back to 1980-ish.

    I can send you a real one if you need ^_^  I paid what it's worth, but it wouldn't be worth the cost of postage, except that maybe you need it ^_^  I was going to give it to a relative, but then remembered that I wouldn't be able to teach the relative to set the date and time every time they boot, so I still have it.

  • We can use the key from VS inside the <integration> <microsoft> tags in the

    vmc to disable host timesync.

    <components>

    <host_time_sync>

        <enabled type="boolean">false</enabled>

    </host_time_sync>

    </components>

  • I dont know why Microsoft is so much concerned about Virtual environment to be used as piracy purpose as when working, developing, specially troubleshooting, in many case I find I am in need to set different time format for my virtual OS to test and troubleshoot certain issues with my projects.

    @Ben

    Sir, Concept of Virtual OS came as to allow user not to alter anything on his host system and test / play with his guest os as what ever way he would want !!

    Changing the hosts date and time is not quite acceptable (other running services are there too)  as when I am using the guest os for testing reason !!

  • How would you explain the virtual machine having a time difference of one hour, compaired to the host at startup????

  • Everytime we start our Applicaton the Virtual Machine has a one hour difference from the host. How is that?? and how can i change it to match?

  • This is indeed, lame.  Piracy is a weak excuse, as other VM systems allow this, such as virtualbox, which I am now going to use instead.

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