If you're reading this guide, you probably have a server where you're getting the following error message after a cPanel update failed:
[2020-05-26 16:55:38 +0000] E Blocker found: Newer releases of cPanel & WHM
are not compatible with your operating system. Upgrade your OS, or use
the Update Preferences screen to select a Long-Term Support release for
use with your OS. Starting with version 88, cPanel & WHM supports 64-bit
versions of CentOS 7+, Red Hat Enterprise Linux 7+, and CloudLinux® 6+ only.
Please see our OS End of Life policy for more information.
This means you are using the CentOS 6 operating system on your cPanel server, which last received full updates in May 2017. In order to update to cPanel version 88 we do require you to be running CentOS 7, or be using the CloudLinux 6 or 7 operating systems. If you can't perform a full migration at this time, you can purchase and install CloudLinux on your CentOS 6 machine, and that will allow you to continue to receive updates and update the cPanel software. We offer those licenses directly through our store here: https://www.cpanel.net/products/add-ons/#cloudlinux
You can find more details about this in our blog post here: https://blog.cpanel.com/centos-6-eol-cloudlinux-6-os-and-you/
There is always up-to-date information posted on our forums that goes into more detail about the extended supported for CloudLinux 6: https://forums.cpanel.net/threads/questions-about-extended-support-for-cloudlinux-6.658021/