Upgrading CentOS Stream 8 to CentOS Stream 9 using Leapp
Quoting: Upgrading CentOS Stream 8 to CentOS Stream 9 using Leapp | die-welt.net —
Contrary to distributions like Debian and Fedora, RHEL can't be upgraded using the package manager alone.
Instead there is a tool called Leapp that takes care of orchestrating the update and also includes a set of checks whether a system can be upgraded at all. Have a look at the RHEL documentation about upgrading if you want more details on the process itself.
You might have noticed that the title of this post says "CentOS Stream" but here I am talking about RHEL. This is mostly because Leapp was originally written with RHEL in mind.