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8.2. Required Time Management Parameters for Red Hat Enterprise Linux Guests

For certain Red Hat Enterprise Linux guest virtual machines, additional kernel parameters are required for their system time to be synchronised correctly. These parameters can be set by appending them to the end of the /kernel line in the /etc/grub2.cfg file of the guest virtual machine.

Note

Red Hat Enterprise Linux 5.5 and later, Red Hat Enterprise Linux 6.0 and later, and Red Hat Enterprise Linux 7 use kvm-clock as their default clock source. Running kvm-clock avoids the need for additional kernel parameters, and is recommended by Red Hat.
The table below lists versions of Red Hat Enterprise Linux and the parameters required on the specified systems.

Table 8.1. Kernel parameter requirements

Red Hat Enterprise Linux version Additional guest kernel parameters
7.0 and later on AMD64 and Intel 64 systems with kvm-clock Additional parameters are not required
6.1 and later on AMD64 and Intel 64 systems with kvm-clock Additional parameters are not required
6.0 on AMD64 and Intel 64 systems with kvm-clock Additional parameters are not required
6.0 on AMD64 and Intel 64 systems without kvm-clock notsc lpj=n

Note

The lpj parameter requires a numeric value equal to the loops per jiffy value of the specific CPU on which the guest virtual machine runs. If you do not know this value, do not set the lpj parameter.