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18.19. Configuring Clock Sources

To list the available clock sources on your system, issue the following commands:
~]$ cd /sys/devices/system/clocksource/clocksource0/
clocksource0]$ cat available_clocksource
kvm-clock tsc hpet acpi_pm 
clocksource0]$ cat current_clocksource
In the above example, the kernel is using kvm-clock. This was selected at boot time as this is a virtual machine. Note that the available clock source is architecture dependent.
To override the default clock source, append the clocksource directive to the end of the kernel's GRUB 2 menu entry. Use the grubby tool to make the change. For example, to force the default kernel on a system to use the tsc clock source, enter a command as follows:
~]# grubby --args=clocksource=tsc --update-kernel=DEFAULT
The --update-kernel parameter also accepts the keyword ALL, or a comma separated list of kernel index numbers.
See Chapter 25, Working with GRUB 2 for more information on making changes to the GRUB 2 menu.