1. Firstly, open an SSH client into your EC2 instance.

2. Then run the following commands to find the current and available clock sources:

cat /sys/devices/system/clocksource/clocksource0/current_clocksource
xen

4. For listing the clock source, we can use the following command:

cat /sys/devices/system/clocksource/clocksource0/available_clocksource
xen tsc hpet acpi_pm

2. Setting the current clock source to a different value

1. First, we have to run bash as a superuser to override the current_clocksource using the following:

sudo bash -c 'echo tsc > /sys/devices/system/clocksource/clocksource0/current_clocksource'

2. Then run the following dmesg command to view the kernel messages:

dmesg | less

If the override was successful, we will get the following:

clocksource: Switched to clocksource tsc

Note: Rebooting the system causes the Linux kernel to reset the clock source.

3. Setting a clock source during the system boot loader

1. First, we have to set clocksource in the kernel command line parameter.

For example, if we use grub2 and want to set the clock source to “tsc”, we must edit the /etc/default/grub file and add clocksource=tsc tsc=reliable for the GRUB_CMDLINE_LINUX option:

GRUB_CMDLINE_LINUX="console=tty0 crashkernel=auto console=ttyS0,115200 clocksource=tsc tsc=reliable"

2. Now, we can generate the grub.cfg file using the following:

grub2-mkconfig -o /boot/grub2/grub.cfg

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Conclusion

To conclude, we saw the steps that our Support Techs follow to manage the source for our customers.