hwclock not updated when I unpause guest

[940607]

Unlike Windows guests, when I unpause or restore my Archlinux guest, the clock does not update.

How to fix this? Don't suggest NTP - all should work without it.

Code: Select all

<?xml version="1.0"?>
<!--
** DO NOT EDIT THIS FILE.
** If you make changes to this file while any VirtualBox related application
** is running, your changes will be overwritten later, without taking effect.
** Use VBoxManage or the VirtualBox Manager GUI to make changes.
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[mpack]

How to fix this? Don't suggest NTP - all should work without it.

Really? Then you must know something I don't, since I was under the impression that it's up to the guest when and how it updates its own clock.

[940607]

it's up to the guest when and how it updates its own clock.

Compare with mouse and keyboard. RTC is a virtual device too and should be set by the host. Maybe linux is being too smart and updates hwclock when woken, but I don't have any confirmation of that

[Perryg]

The update of the guest "hwclock" with VirtualBox requires the guest additions being installed ( in the guest ).
This also depends on how long the guest is paused. If say it was paused a matter of a few minutes. It can take hours for the guest to sync.
You can also control this.

I found that setting the threshold to 1000 actually makes VBox reset the clock sooner. ( YMMV )

Code: Select all

As su/sudo on guest to test
VBoxService --timesync-set-threshold 1000

Or run this on the host to make permanent 
VBoxManage guestproperty set <guests name> "/VirtualBox/GuestAdd/VBoxService/--timesync-set-threshold" 1000

[mpack]

Compare with mouse and keyboard. RTC is a virtual device too and should be set by the host.

That's correct - and like the RTC, it's also up to the guest when it reads the keyboard, and what keyboard map it applies. Just because the VM simulated hardware is available doesn't guarantee that the guest will use it as you expect.

In particular, some guests don't read their RTC continuously, instead they init a counter on startup and thereafter use a timer int to update it, and derive their clock from that too. If the timer int stops mysteriously, e.g. because the VM was suspended, then the clock will be off. Whether Arch Linux works this way I can't say.

I think if you install the GAs then VirtualBox may do something to force the guest to update quicker, but I don't even know if official GAs are available for Arch Linux - it's barely mentioned in the manual.

[940607]

The additions are installed. I think I found the reason:

--timesync-set-threshold

The absolute drift threshold, given as milliseconds where to start setting the time instead of trying to smoothly adjust it. The default is 20 minutes.

However, on Windows the time is set even after a small pause, e.g. 2 minutes.

$ VBoxManage guestproperty get "win2003-1" /VirtualBox/GuestAdd/VBoxService/--timesync-set-threshold
No value set!
$ VBoxManage guestproperty get "arch" /VirtualBox/GuestAdd/VBoxService/--timesync-set-threshold
No value set!

[Perryg]

I posted the fix above. Did you try it or are you thinking it is incorrect?

[940607]

Yes, your fix works. What bothers me now is why Windows guests don't need this fix.

[Perryg]

Since it was never broken I did not spend any time trying to figure out why it worked.