Removing the default kernel aka the loaded kernel in CentOS 8 maybe challenging because the package is protected and cannot be removed by the yum or dnf.
Here is the case: an elrepo kernel-ml loaded and the dnf prints it cannot remove the package, because it is protected:
[root@srv ~]# dnf remove kernel-ml kernel-ml-core kernel-ml-modules
Problem: The operation would result in removing the following protected packages: kernel-ml-core
(try to add '--skip-broken' to skip uninstallable packages or '--nobest' to use not only best candidate packages)
[root@srv ~]# uname -a
Linux srv.localhost 5.10.4-1.el8.elrepo.x86_64 #1 SMP Tue Dec 29 11:04:23 EST 2020 x86_64 x86_64 x86_64 GNU/Linux
[root@srv ~]# grubby --default-kernel
The system is booted up with the kernel we are trying to remove, which is impossible.
The solution is to set a new default kernel and load it. Then dnf will be able to remove the first kernel.
For CentOS 7, just use the yum instead of dnf command.
Using grubby is really easy and straightforward:
STEP 1) List all installed and available to boot kernels
[root@srv ~]# grubby --set-default "/boot/vmlinuz-4.18.0-259.el8.x86_64"
The default is /boot/loader/entries/45e12f0814fd4947b99cbdcb88950361-4.18.0-259.el8.x86_64.conf with index 1 and kernel /boot/vmlinuz-4.18.0-259.el8.x86_64
Installing CentOS 8 in relatively old hardware maybe a real challenge because of an old hardware device like storage, network, or both.
This article shows how to make the CentOS 8 Installation wizard detect the storage – a hardware controller AOC-USAS2LP-H8iR (smc2108 with LSI 2108). Unfortunately, the CentOS 8 (in fact, RHEL 8 removed the support, too) team decided to remove support for the LSI SAS2008/2108/2116 storage controllers by removing the “megaraid_sas” kernel driver. There are still servers in production with similar controllers, which were sold 4-5 years ago from the big vendors such as DELL, HP, and so on.
The method here is to boot the installation CD/USB with modified kernel boot parameters to include an URL link to the installation driver iso (where the megaraid_sas driver is included).
The offered way to load the megaraid_sas (or any other driver) includes:
Configure the network of the server to be able to download the driver ISO in the early stage of the CentOS 8 Installation Wizard. Add boot parameters to set up a valid network configuration.
The installation CD/USB can download an iso with kernel drivers. And of course, to download a file from the Internet a network should be set in the earliest stage of the CentOS 8 installation wizard.
The added string to the boot CD/USB CentOS 8 Installation disk is:
SCREENSHOT 1) Select with the arrows “Install CentOS Linux 8” and hit “TAB” button to edit the boot parameters.
As shown in the picture just add ” inst.dd=https://elrepo.org/linux/dud/el8/x86_64/dd-megaraid_sas-07.710.50.00-1.el8_2.elrepo.iso ip=10.10.10.10::10.10.10.1:255.255.255.0::enp8s0f0:off nameserver=188.8.131.52″. The “inst.dd” instructs the installation wizard where are the driver ISO located. The “ip” and “nameserver” command just sets a proper network in the early stage of the CentOS 8 Installation wizard to be able to download the driver ISO. Setting the network by these parameters is really important, because the download of the driver iso happens in this early stage of loading the installation wizard. Replace the IP and the whole network configuration if needed.