Ugo Bellavance wrote:

Maybe the clock is sync'd with the host?

Correct, and it's even done automatically.

Just run NTP on the dom0 and all domUs will have the correct time.

On Thu, 23 Apr 2009, Ugo Bellavance wrote:

Mintairov Mihail a écrit :

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Hello All, I have a problem with hwclock on centos 5.3. in xen guest environment.

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# hwclock --debug hwclock from util-linux-2.13-pre7 hwclock: Open of /dev/rtc failed, errno=19: No such device. No usable clock interface found. Cannot access the Hardware Clock via any known method.

yes - this also shows up in the dmesg at boot time in the domU. I noted it when doing LSB testing, as part of their 3.2 suite wanted to tickle the hardware clock.

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So, I'm afraid that I can not change my time by ntp.

In CentOS mailing list I found a thread "hwclock and util-linux on 5.3", but there is still no answer and discussion stopped. Maybe someone knows the solution of this problem.

Maybe the clock is sync'd with the host?

essentially this is the case -- the host (the dom0) has exclusive write access as to the clock. -- There is intentionally should be no solution to permit a domU to alter the hwclock, as a domU should not be able to affect the domO's clock.

To permit a domU to do do so would permit the client to control the master outer ring zero's crontab, atd, and such

Kerberos attacks [keeping a ticket in force longer than intended], and more also come to mind, if a arbitrary domU could control the clock

- Russ herrold