Red Hat ENTERPRISE LINUX 5.5 - TECHNICAL NOTES Manual page 144

Chapter 1. Package Updates
interactive Bourne shell script, fix_clock_drift.sh, which, when run as the superuser, inspects various
system parameters to determine if the guest on which it is run is susceptible to clock drift under load
and, if so, then creates a new "grub.conf.kvm" file in the /boot/grub/ directory. This file contains a
kernel boot line with additional kernel parameters that allow the kernel to account for and prevent
significant clock drift on the KVM guest. Note also that the ntpd service must be running on the KVM
guest for the clock drift to be corrected.
Important: after running fix_clock_drift.sh as the superuser, and once the script has created the
"grub.conf.kvm" file, then the guest's current "grub.conf" file should be backed up manually by the
system administrator, the new "grub.conf.kvm" file should be manually inspected to ensure that it is
identical to "grub.conf" with the exception of the additional boot line parameters, the "grub.conf.kvm"
file should finally be renamed "grub.conf", and the guest should be rebooted.
Users of Red Hat Enterprise Linux KVM guests that are affected by significant clock drift are advised
to upgrade to this updated package, which resolves this issue.
1.92.2. RHBA-2010:0238: bug fix and enhancement update
An updated ktune package that fixes a clock drift bug in Red Hat Enterprise Linux guests and adds
support for the ktune.d directory is now available.
The ktune package includes settings for server performance-tuning.
This updated ktune package fixes the following bug:
* when running a Red Hat Enterprise Linux KVM guest under heavy load, the guest's system clock
had the tendency to drift by an amount correlated with the system load. This ktune update provides
an interactive Bourne shell script, fix_clock_drift.sh, which, when run as with root privileges, inspects
various system parameters to determine if the guest on which it is run is susceptible to clock drift
under load and, if so, creates a new "grub.conf.kvm" file in the /boot/grub/ directory. This file contains
a kernel boot line with additional kernel parameters that allow the kernel to account for and prevent
significant clock drift on the KVM guest.
Note: the ntpd service must be running on the KVM guest for the clock drift to be corrected.
Important: this script does not replace the existing grub.conf file. If running fix_clock_drift.sh creates
the file "grub.conf.kvm" the system administrator must set the new file up manually as follows: back up
the guest's current "grub.conf" file; inspect "grub.conf.kvm" and ensure it is identical to "grub.conf" with
the exception of the additional boot line parameters; re-name "grub.conf.kvm" to "grub.conf"; reboot
the guest.
This update also adds the following enhancement:
* support for ktune.d directory has been added to load additional sysctl profiles. Each profile could also
provide a script for settings which can not be done with sysctl. The script will get an option which will
be start or stop according to the ktune service command used for ktune.
Users of Red Hat Enterprise Linux KVM guests, especially those affected by significant clock drift, are
advised to upgrade to this updated package, which resolves this issue and adds this enhancement.
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https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=518039
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https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=516652
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https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=496940
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(BZ#516652 )
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(BZ#518039 )
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