Re: [Xen-users] Disabling clock set in PV boot?

Evan Lavelle
Wed, 04 Nov 2009 15:53:33 -0000

A partial answer, for anyone who comes this way in the future:

> Is there some way to prevent Xen from setting the clock for a PV guest
> while booting it?

The answer seems to be no. ''hwclock'' doesn''t work (as
you''d expect), and
  ''date'' is disabled until some point in the boot sequence
which I
haven''t identified. You can''t wait till booting has completed
to fix the
date, because by that time you can have thousands of files which have
been incorrectly stamped.

If you really want a guest with an independent system time, then it
looks like it has to be hvm. When ''hwclock'' is run from
rc.sysinit it
sometimes sets the date to the Dom0 date (on a cold boot?), and
sometimes sets it to the last time at which the DomU shut down. This
isn''t a problem, because you can insert a ''date''
command immediately
after ''hwclock'' and it works.

You probably also have to turn off SELinux in the guest; the dom0 date
leaks through somehow during the boot. There are also a few files in
/proc which occasionally seem to get timestamped 3 days in the future,
but this is easy enough to fix.

-Evan