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How to Manage clock source for EC2 instance

by | Jul 22, 2021

Wondering how to manage clock source for EC2 instance? We can help you!

Using SSH client is one of the method, to find the current clock source, list the available clock sources, or change the clock source.

Here at Bobcares, we help our customers to manage clock source for their EC2 instance as a part of our Server Management Services.

Today let’s see how our Support Engineers do this using an SSH client for our customers.

How to Manage clock source for EC2 instance

Now, we will see the steps that our Support techs follow for managing clock source for EC2 instance.

Steps for managing clock source:

Following are the steps to mange clock source using SSH client for EC2 instance.

1. Finding the clock source

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

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


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