This is a notice to all those running Scientific Linux 5.0 as a xen host for virtual machines. The kernel security update (kernel-2.6.18-53.1.4.el5) that went out earlier this week contained changes dealing with how it deals with the xen host. Because of these changes, if you update your kernel and reboot into this new kernel without changing xen, you will not be able to host any virtual machines. Today we have sent out the new xen and libvirt that work with the new kernel. The problem is that the kernel is *not* automatically updated by the nightly yum cron job. xen and libvirt *are* automatically updated by the nightly yum cron job. What should you do? Update both as soon as possible. How? yum update (check whatever you want to check) (shut down all your currently running virtual machines) reboot If xen get's updated before the kernel changes, will my virtual machines die or go crazy? In our tests the answer is no. Both fully-virtualized and para-virtulized machines stayed up and stable after the xen was changed. But we could not reboot them. Once one went down for whatever reason, it stayed down. But the others stayed up and stable even when several other virtual machines were brought down. If your xen is changed before the kernel is changed, you cannot start any more virtual guests. But any currently running virtual guests will remain running. Please note: We were not able to test for long periods of time. So please don't put off rebooting into the new kernel for a month or two. Thank you for your cooperation. We apologize for any inconvenience. Troy Dawson -- __________________________________________________ Troy Dawson [log in to unmask] (630)840-6468 Fermilab ComputingDivision/LCSI/CSI DSS Group __________________________________________________