Custom time

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Hello,

this may be a stupid question, but I need to change the system time before the operating system starts (boot). I don't know how to get into the bios menu (if there is one at all) and if I try to change the time after the OS has booted, it is automatically resetted to the correct one. Is it possible to disable this "function"?

[vbox4me2]

You have to remove the GA in the VM for this.

[MarkCranness]

The manual (section 9.15) mentions a TSCTiedToExecution option, but I think that may cause clock skew.

Try this (undocumented) setting while the VM is shutdown:

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VBoxManage setextradata "My VM" "VBoxInternal/TM/UTCOffset" <nanoSeconds>

<nanoSeconds> is a signed 64 bit integer being the offset from UTC (I think)
Set it to -86400000000000 to offset the VM time back one day.

The clock ticks will then still be in sync, but with an offset applied.

Edit: This can also be set using:

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VBoxManage modifyvm "My VM" --biossystemtimeoffset <msec>

... this should set the VM clock to be in sync with the host clock, but <msec> (milliseconds) offset. Negative numbers put the VM clock in the past, positive numbers put the VM into the future.