Problem: During installation of CentOS the installer screen goes black. The terminal multiplexer is running in virtual console 1. To switch from the graphical installation environment to tmux, press Ctrl+Alt+F1. To go back to the main installation interface which runs in virtual console 6, press Ctrl+Alt+F6. Available tmux Windows Shortcut Contents Ctrl+b 1 Main installation […]


Using package-cleanup command which is a part of yum-utils package we can uninstall any number of old kernels automatically. As an example using --oldkernels --count=2 option with package-cleanup command the command will remove all unused kernel while keeping last three most recent kernel versions installed.


list installed kernels

remove kernels no longer needed; listed above


By default CentOS will keep last 5 kernels installed on your system. This behavior is defined by installonly_limit=5 line within /etc/yum.conf file. Update the /etc/yum.conf configuration file appropriately to keep desired number of old kernels on your system after update. The minimum value to be set is 2.

Example of /etc/yum.conf configuration file to keep only last two kernel versions:

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ZFS – Downgrade Commands for Centos:

To do the downgrade/re-install dance: