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The following table lists wallclock settings for Linux VMs:
Guest OS Dependent wallclock Independent wallclock
CentOS 4.x Default Optional
CentOS 5.x (32-/64-bit) Default Optional
CentOS 6.x (32-/64-bit) Not supported Default
Red Hat Enterprise Linux 4.x (32-bit) Default Optional
Red Hat Enterprise Linux 5.x (32-/64-bit) Default Optional
Red Hat Enterprise Linux 6.x (32-/64-bit) Not supported Default
OEL 5.x (32-/64-bit) Default Optional
OEL 6.x (32-/64-bit) Not supported Default
SLES 10.x (32-/64-bit) Default Optional
SLES 11.x (32-/64-bit) Default Optional
Debian 6.0 (32-/64-bit) Not supported Default
Ubuntu 10.04 (32-/64-bit) Not supported Default
Ubuntu 12.04 (32-/64-bit) Not supported Default
Important:
• For Linux guests that support dependent wallclock, Citrix recommends enabling
independent wallclock setting and using NTP inside the VM.
• For Linux guests that use an independent wallclock, Citrix highly recommends running a
reliable NTP service on the Linux VMs and the XenServer host.
Refer to the following section to set the independent wallclock time.
To set individual Linux VMs to maintain independent times
1. From a root prompt on the VM, run the command: echo 1 > /proc/sys/xen/independent_wallclock
2. This can be persisted across reboots by changing the /etc/sysctl.conf configuration file and adding:
# Set independent wall clock time
xen.independent_wallclock=1
3. As a third alternative, independent_wallclock=1 may also be passed as a boot parameter to the VM.
Note:
When installing a new Linux VM, make sure that you change the time-zone from the default
UTC to your local value (see Section B.1, “Release Notes” for specific distribution instructions).
9.8. Installing a VM from Reseller Option Kit (BIOS-locked) Media
A XenServer VM can be:
• BIOS-generic: the VM has generic XenServer BIOS strings;
• BIOS-customized: the VM has a copy of the BIOS strings of a particular server in the pool;
