As you might be aware, CentOS 8 is end of life since the 31st of December 2021. If you are still using and running CentOS 8, you might want to migrate to some alternative distributions in order to keep a Red Hat compatibility.

Those alternative distributions might be chosen between :

  • Rocky Linux
  • AlmaLinux
  • Red Hat Enterprise Linux
  • Oracle Linux

We are already having a few blogs describing how to migrate to Rocky Linux, AlmaLinux and Red Hat Enterprise Linux :

In this blog we will see how to migrate from CentOS 8 to Oracle Linux 8.

centos2ol.sh Oracle Script

Oracle provides a script to be able to switch from CentOS Linux 6, 7 or 8 to its equivalent version of Oracle Linux. The script as well as requirements, limitations, know issues and explanations can be found on the oracle GitHub website.

Please read carefully the limitations part. Access to both CentOS and Oracle Linux yum repositories is mandatory.

Before starting the migration using the script it is very important to ensure having a complete working backup of the system.

Migration demo

I have setup a linux environment running CentOS 8.

[[email protected] ~]# cat /etc/centos-release
CentOS Linux release 8.4.2105

We need to download the centos2ol.sh script and move it to the CentOS Linux server to be migrated. This can be done using curl command.

[[email protected] ~]# curl -O https://raw.githubusercontent.com/oracle/centos2ol/main/centos2ol.sh
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 22928  100 22928    0     0   120k      0 --:--:-- --:--:-- --:--:--  121k

[[email protected] ~]# ls -l centos*.sh
-rw-r--r--. 1 root root 22928 Jun  8 08:13 centos2ol.sh

Let’s first check the current kernel and kernel executable files :

[[email protected] ~]# uname -a
Linux centosmigr 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun 1 16:14:33 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

[[email protected] ~]# ls -l /boot
total 153964
-rw-r--r--. 1 root root   192095 Jun  1  2021 config-4.18.0-305.3.1.el8.x86_64
drwxr-xr-x. 3 root root       17 Jun  2  2021 efi
drwxr-xr-x. 2 root root       39 Jun  2  2021 grub
drwx------. 4 root root       83 Jun  8 08:14 grub2
-rw-------. 1 root root 64383726 Jun  2  2021 initramfs-0-rescue-40ec35b37a254049be3d85f9173b39a1.img
-rw-------. 1 root root 51128711 Jun  2  2021 initramfs-4.18.0-305.3.1.el8.x86_64.img
-rw-------. 1 root root 17727685 Jun  3 14:44 initramfs-4.18.0-305.3.1.el8.x86_64kdump.img
drwxr-xr-x. 3 root root       21 Jun  2  2021 loader
-rw-------. 1 root root  4164308 Jun  1  2021 System.map-4.18.0-305.3.1.el8.x86_64
-rwxr-xr-x. 1 root root 10026120 Jun  2  2021 vmlinuz-0-rescue-40ec35b37a254049be3d85f9173b39a1
-rwxr-xr-x. 1 root root 10026120 Jun  1  2021 vmlinuz-4.18.0-305.3.1.el8.x86_64

And my current centos linux package :

[[email protected] ~]# rpm -qa | grep -i centos
centos-linux-repos-8-2.el8.noarch
centos-logos-85.5-1.el8.x86_64
centos-linux-release-8.4-1.2105.el8.noarch
centos-gpg-keys-8-2.el8.noarch

We can run the conversion script from Oracle with centos user knowing it has the sudo priviledge. The option of the script are the following one :

[[email protected] ~]$ sudo bash /root/centos2ol.sh -h
Usage: centos2ol.sh [OPTIONS]

OPTIONS
-h
        Display this help and exit
-k
        Do not install the UEK kernel and disable UEK repos
-r
        Reinstall all CentOS RPMs with Oracle Linux RPMs
        Note: This is not necessary for support
-V
        Verify RPM information before and after the switch

Note that in can we would prefer to migrate to the Red Hat compatible Kernel and not to UEK, we can use the option -k. This option will not install the UEK kernel and also disable UEK repository.

We will run the script with the -V option.

[[email protected] ~]$ sudo bash /root/centos2ol.sh -V

After a first few checks, the script will backup and remove CentOS repository files, followed by a download and an installation of Oracle Linux repositories.

Backing up and removing old repository files...
Removing CentOS-specific yum configuration from /etc/yum.conf

We can easily confirm this by checking the yum repository files.

[[email protected] tmp]$ ls -l /etc/yum.repos.d/
total 60
-rw-r--r--. 1 root root  891 Jun  8 08:34 CentOS-Linux-AppStream.repo.disabled
-rw-r--r--. 1 root root  876 Jun  8 08:34 CentOS-Linux-BaseOS.repo.disabled
-rw-r--r--. 1 root root 1302 Jun  8 08:34 CentOS-Linux-ContinuousRelease.repo.disabled
-rw-r--r--. 1 root root  490 Jun  8 08:34 CentOS-Linux-Debuginfo.repo.disabled
-rw-r--r--. 1 root root  904 Jun  8 08:34 CentOS-Linux-Devel.repo.disabled
-rw-r--r--. 1 root root  876 Jun  8 08:34 CentOS-Linux-Extras.repo.disabled
-rw-r--r--. 1 root root  891 Jun  8 08:34 CentOS-Linux-FastTrack.repo.disabled
-rw-r--r--. 1 root root  912 Jun  8 08:34 CentOS-Linux-HighAvailability.repo.disabled
-rw-r--r--. 1 root root  865 Jun  8 08:34 CentOS-Linux-Media.repo.disabled
-rw-r--r--. 1 root root  878 Jun  8 08:34 CentOS-Linux-Plus.repo.disabled
-rw-r--r--. 1 root root  896 Jun  8 08:34 CentOS-Linux-PowerTools.repo.disabled
-rw-r--r--. 1 root root 1070 Jun  8 08:34 CentOS-Linux-Sources.repo.disabled
-rw-r--r--. 1 root root 2961 Jun  8 08:35 oracle-linux-ol8.repo
-rw-r--r--. 1 root root  470 May 11 22:21 uek-ol8.repo
-rw-r--r--. 1 root root  243 May 11 22:21 virt-ol8.repo

The CentOS repositories have been disabled and the new Oracle Linux repositories have been installed.

The script will then download latest Oracle Linux release package.

Downloading Oracle Linux release package...
Oracle Linux 8 BaseOS Latest (x86_64)                                                                                                                                                                                         146 MB/s |  46 MB     00:00
Oracle Linux 8 Application Stream (x86_64)                                                                                                                                                                                    131 MB/s |  36 MB     00:00
Latest Unbreakable Enterprise Kernel Release 6 for Oracle Linux 8 (x86_64)                                                                                                                                                    152 MB/s |  48 MB     00:00
Last metadata expiration check: 0:00:08 ago on Wed 08 Jun 2022 08:34:52 AM UTC.
(1/3): oraclelinux-release-el8-1.0-23.el8.x86_64.rpm                                                                                                                                                                          567 kB/s |  21 kB     00:00
(2/3): redhat-release-8.6-0.1.0.1.el8.x86_64.rpm                                                                                                                                                                              497 kB/s |  19 kB     00:00
(3/3): oraclelinux-release-8.6-1.0.5.el8.x86_64.rpm                                                                                                                                                                           1.6 MB/s |  77 kB     00:00

In order to finally start switching old CentOS release package with Oracle Linux.

Switching old release package with Oracle Linux...

The base packages for CentOS will be removed and the one for Oracle Linux will be installed.

Enabling ol8_appstream which replaces appstream
Enabling ol8_baseos_latest which replaces baseos
Installing base packages for Oracle Linux...
Oracle Linux 8 BaseOS Latest (x86_64)                                                                                                                                                                                         202 kB/s | 3.6 kB     00:00
Oracle Linux 8 Application Stream (x86_64)                                                                                                                                                                                    204 kB/s | 3.9 kB     00:00
> Package basesystem-11-5.el8.noarch is already installed.
Package initscripts-10.00.15-1.el8.x86_64 is already installed.
Package grub2-pc-1:2.02-99.el8.x86_64 is already installed.
Package grubby-8.40-41.el8.x86_64 is already installed.
> ==============================================================================================================================================================================================================================================================
 Package                                                       Architecture                                    Version                                                                       Repository                                                  Size
==============================================================================================================================================================================================================================================================
Installing:
 kernel-uek                                                    x86_64                                          5.4.17-2136.307.3.6.el8uek                                                    ol8_UEKR6                                                  109 M
 oracle-logos                                                  x86_64                                          84.5-1.0.1.el8                                                                ol8_baseos_latest                                          1.4 M
 plymouth                                                      x86_64                                          0.9.4-11.20200615git1e36e30.0.1.el8                                           ol8_appstream                                              127 k
Upgrading:
 grub2-common                                                  noarch                                          1:2.02-123.0.3.el8                                                            ol8_baseos_latest                                          895 k
 grub2-pc                                                      x86_64                                          1:2.02-123.0.3.el8                                                            ol8_baseos_latest                                           45 k
 grub2-pc-modules                                              noarch                                          1:2.02-123.0.3.el8                                                            ol8_baseos_latest                                          924 k
 grub2-tools                                                   x86_64                                          1:2.02-123.0.3.el8                                                            ol8_baseos_latest                                          2.0 M
 grub2-tools-extra                                             x86_64                                          1:2.02-123.0.3.el8                                                            ol8_baseos_latest                                          1.1 M
 grub2-tools-minimal                                           x86_64                                          1:2.02-123.0.3.el8                                                            ol8_baseos_latest                                          213 k
 grubby                                                        x86_64                                          8.40-42.0.1.el8                                                               ol8_baseos_latest                                           50 k
 tuned                                                         noarch                                          2.18.0-2.0.1.el8                                                              ol8_baseos_latest                                          318 k
Installing dependencies:
 grub2-tools-efi                                               x86_64                                          1:2.02-123.0.3.el8                                                            ol8_baseos_latest                                          478 k
 linux-firmware                                                noarch                                          999:20220304-999.13.gitf011ccb4.el8                                           ol8_baseos_latest                                          216 M
 linux-firmware-core                                           noarch                                          999:20220304-999.13.gitf011ccb4.el8                                           ol8_baseos_latest                                          509 k
 plymouth-core-libs                                            x86_64                                          0.9.4-11.20200615git1e36e30.0.1.el8                                           ol8_appstream                                              122 k
 plymouth-scripts                                              x86_64                                          0.9.4-11.20200615git1e36e30.0.1.el8                                           ol8_appstream                                               44 k
Removing:
 centos-gpg-keys                                               noarch                                          1:8-2.el8                                                                     @anaconda                                                  3.3 k
 centos-linux-release                                          noarch                                          8.4-1.2105.el8                                                                @anaconda                                                   25 k
 centos-logos                                                  x86_64                                          85.5-1.el8                                                                    @anaconda                                                  698 k
 python3-syspurpose                                            x86_64                                          1.28.13-2.el8                                                                 @anaconda                                                  138 k

Transaction Summary
==============================================================================================================================================================================================================================================================
Install  8 Packages
Upgrade  8 Packages
Remove   4 Packages

Total download size: 333 M
Downloading Packages:
(1/16): linux-firmware-core-20220304-999.13.gitf011ccb4.el8.noarch.rpm                                                                                                                                                         13 MB/s | 509 kB     00:00
(2/16): grub2-tools-efi-2.02-123.0.3.el8.x86_64.rpm                                                                                                                                                                            11 MB/s | 478 kB     00:00
(3/16): plymouth-0.9.4-11.20200615git1e36e30.0.1.el8.x86_64.rpm                                                                                                                                                                21 MB/s | 127 kB     00:00
...
...
...
Running transaction
  Preparing        :                                                                                                                                                                                                                                      1/1
  Running scriptlet: grub2-common-1:2.02-123.0.3.el8.noarch                                                                                                                                                                                               1/1
  Upgrading        : grub2-common-1:2.02-123.0.3.el8.noarch                                                                                                                                                                                              1/28
  Upgrading        : grub2-tools-minimal-1:2.02-123.0.3.el8.x86_64                                                                                                                                                                                       2/28
...
...
...
  Installing       : plymouth-scripts-0.9.4-11.20200615git1e36e30.0.1.el8.x86_64                                                                                                                                                                         7/28
  Installing       : plymouth-0.9.4-11.20200615git1e36e30.0.1.el8.x86_64                                                                                                                                                                                 8/28
  Installing       : linux-firmware-core-999:20220304-999.13.gitf011ccb4.el8.noarch                                                                                                                                                                      9/28
...
...
...
  Verifying        : centos-logos-85.5-1.el8.x86_64                                                                                                                                                                                                     27/28
  Verifying        : python3-syspurpose-1.28.13-2.el8.x86_64                                                                                                                                                                                            28/28

Upgraded:
  grub2-common-1:2.02-123.0.3.el8.noarch  grub2-pc-1:2.02-123.0.3.el8.x86_64  grub2-pc-modules-1:2.02-123.0.3.el8.noarch  grub2-tools-1:2.02-123.0.3.el8.x86_64  grub2-tools-extra-1:2.02-123.0.3.el8.x86_64  grub2-tools-minimal-1:2.02-123.0.3.el8.x86_64
  grubby-8.40-42.0.1.el8.x86_64           tuned-2.18.0-2.0.1.el8.noarch
Installed:
  grub2-tools-efi-1:2.02-123.0.3.el8.x86_64         kernel-uek-5.4.17-2136.307.3.6.el8uek.x86_64                linux-firmware-999:20220304-999.13.gitf011ccb4.el8.noarch             linux-firmware-core-999:20220304-999.13.gitf011ccb4.el8.noarch
  oracle-logos-84.5-1.0.1.el8.x86_64                plymouth-0.9.4-11.20200615git1e36e30.0.1.el8.x86_64         plymouth-core-libs-0.9.4-11.20200615git1e36e30.0.1.el8.x86_64         plymouth-scripts-0.9.4-11.20200615git1e36e30.0.1.el8.x86_64
Removed:
  centos-gpg-keys-1:8-2.el8.noarch                           centos-linux-release-8.4-1.2105.el8.noarch                           centos-logos-85.5-1.el8.x86_64                           python3-syspurpose-1.28.13-2.el8.x86_64

Complete!

We can then see a nice message that the switch was successful and that the system will now sync with the oracle Linux repositories.

Switch successful. Syncing with Oracle Linux repositories.                                                                                                                                                                                 204 kB/s | 3.9 kB     00:00

Syncing means upgrading all packages to Oracle Linux ol8 release and installing the kernel.

Dependencies resolved.
==============================================================================================================================================================================================================================================================
 Package                                                                  Architecture                                  Version                                                                Repository                                                Size
==============================================================================================================================================================================================================================================================
Installing:
 kernel                                                                   x86_64                                        4.18.0-372.9.1.el8                                                     ol8_baseos_latest                                        8.0 M
 kernel-core                                                              x86_64                                        4.18.0-372.9.1.el8                                                     ol8_baseos_latest                                         39 M
 kernel-modules                                                           x86_64                                        4.18.0-372.9.1.el8                                                     ol8_baseos_latest                                         32 M
Upgrading:
 NetworkManager                                                           x86_64                                        1:1.36.0-4.0.1.el8                                                     ol8_baseos_latest                                        2.3 M
 NetworkManager-libnm                                                     x86_64                                        1:1.36.0-4.0.1.el8                                                     ol8_baseos_latest                                        1.8 M
 NetworkManager-team                                                      x86_64                                        1:1.36.0-4.0.1.el8                                                     ol8_baseos_latest                                        153 k
 NetworkManager-tui                                                       x86_64                                        1:1.36.0-4.0.1.el8                                                     ol8_baseos_latest                                        345 k                                                                                                                                                                                 204 kB/s | 3.9 kB     00:00
...
...
...
Transaction Summary
==============================================================================================================================================================================================================================================================
Install    6 Packages
Upgrade  238 Packages

Total download size: 318 M
Downloading Packages:
(1/414): basesystem-11-5.el8.noarch.rpm                                                                                                                                                                                       342 kB/s |  10 kB     00:00
(2/414): bzip2-1.0.6-26.el8.x86_64.rpm                                                                                                                                                                                         13 MB/s |  60 kB     00:00
(3/414): bzip2-libs-1.0.6-26.el8.x86_64.rpm                                                                                                                                                                                    18 MB/s |  48 kB     00:00
(4/414): acl-2.2.53-1.el8.x86_64.rpm                                                                                                                                                                                          1.9 MB/s |  81 kB     00:00
(5/414): brotli-1.0.6-3.el8.x86_64.rpm                                                                                                                                                                                        7.3 MB/s | 323 kB     00:00
(6/414): cracklib-2.9.6-15.el8.x86_64.rpm                                                                                                                                                                                      17 MB/s |  93 kB     00:00
...
...
...

This intent to upgrade, reinstall, install or cleanup packages as well as running packages’ scriptlets.

  Upgrading        : filesystem-3.8-6.el8.x86_64                                                                                                                                                                                                        3/822
  Upgrading        : tzdata-2022a-1.el8.noarch                                                                                                                                                                                                          4/822
  Reinstalling     : fontpackages-filesystem-1.44-22.el8.noarch                                                                                                                                                                                         5/822
...
  Running scriptlet: libproxy-0.4.15-5.2.el8.x86_64                                                                                                                                                                                                   113/822
...
 Installing       : libbpf-0.4.0-3.el8.x86_64                                                                                                                                                                                                        117/822
...
 Cleanup          : glib2-2.56.4-9.el8.x86_64                                                                                                                                                                                                        695/822

As any upgrade, there will be a verification step.

  Verifying        : acl-2.2.53-1.el8.x86_64                                                                                                                                                                                                            1/822
  Verifying        : acl-2.2.53-1.el8.x86_64                                                                                                                                                                                                            2/822
  Verifying        : basesystem-11-5.el8.noarch                                                                                                                                                                                                         3/822

At the end of the package installation we can review the packages that were upgraded, installed or reinstalled.

Upgraded:
  NetworkManager-1:1.36.0-4.0.1.el8.x86_64                   NetworkManager-libnm-1:1.36.0-4.0.1.el8.x86_64                     NetworkManager-team-1:1.36.0-4.0.1.el8.x86_64                      NetworkManager-tui-1:1.36.0-4.0.1.el8.x86_64
  PackageKit-1.1.12-6.0.1.el8.x86_64                         PackageKit-glib-1.1.12-6.0.1.el8.x86_64                            audit-3.0.7-2.el8.2.x86_64                                         audit-libs-3.0.7-2.el8.2.x86_64
...
  virt-what-1.18-13.el8.x86_64                               which-2.21-17.el8.x86_64                                           xfsprogs-5.4.0-1.0.1.el8.x86_64                                    yum-4.7.0-8.0.1.el8.noarch
  yum-utils-4.0.21-11.0.1.el8.noarch                         zlib-1.2.11-18.el8_5.x86_64
Installed:
  NetworkManager-initscripts-updown-1:1.36.0-4.0.1.el8.noarch   kernel-4.18.0-372.9.1.el8.x86_64   kernel-core-4.18.0-372.9.1.el8.x86_64   kernel-modules-4.18.0-372.9.1.el8.x86_64   libbpf-0.4.0-3.el8.x86_64   python3-netifaces-0.10.6-4.el8.x86_64
Reinstalled:
  abattis-cantarell-fonts-0.0.25-6.el8.noarch          acl-2.2.53-1.el8.x86_64                            basesystem-11-5.el8.noarch                     brotli-1.0.6-3.el8.x86_64                           bzip2-1.0.6-26.el8.x86_64
...              xkeyboard-config-2.28-1.el8.noarch             xz-5.2.4-3.el8.x86_64                               xz-libs-5.2.4-3.el8.x86_64

Complete!

At the end of the script execution we can see the output that the sync is successful.

Sync successful.

The system will update the boot loader, generate the new grub configuration file and switch the default boot kernel to the Oracle Linux kernel (UEK).

Updating the GRUB2 bootloader.
Generating grub configuration file ...
done
Switching default boot kernel to the UEK.
Removing yum cache

The option -V has created four log files for listing and verifying the packages before and after the migration.

Creating a list of RPMs installed after the switch
Verifying RPMs installed after the switch against RPM database
Review the output of following files:
/var/tmp/centosmigr-rpms-list-before.log
/var/tmp/centosmigr-rpms-verified-before.log
/var/tmp/centosmigr-rpms-list-after.log
/var/tmp/centosmigr-rpms-verified-after.log

And finally the script will end with an output confirming the switch has been successful completed. A reboot is now more than recommended.

Switch complete.
Oracle recommends rebooting this system.

Checking system after switching to Oracle Linux

Let’s check the new Linux version and confirm we are running Oracle Linux.

[[email protected] ~]$ ls -l /etc/*release*
-rw-r--r--. 1 root root  32 May 13 01:14 /etc/oracle-release
-rw-r--r--. 1 root root 479 May 13 01:14 /etc/os-release
-rw-r--r--. 1 root root  45 May 13 01:14 /etc/redhat-release
lrwxrwxrwx. 1 root root  14 May 13 01:14 /etc/system-release -> oracle-release
-rw-r--r--. 1 root root  31 May 13 01:14 /etc/system-release-cpe

[[email protected] ~]$ cat /etc/oracle-release
Oracle Linux Server release 8.6
[[email protected] ~]$

Let’s check the running kernel.

[[email protected] ~]$ uname -a
Linux centosmigr 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun 1 16:14:33 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

This is the old one, we need to reboot the server first.

[[email protected] ~]$ sudo systemctl reboot
Connection to 172.21.9.153 closed by remote host.
Connection to 172.21.9.153 closed.

After reboot, the system will be started on the new Oracle Linux kernel.

[[email protected] ~]$ uptime
 11:23:08 up 1 min,  1 user,  load average: 1.64, 0.53, 0.19

[[email protected] ~]$ uname -a
Linux centosmigr 5.4.17-2136.307.3.6.el8uek.x86_64 #2 SMP Wed Jun 1 13:54:41 PDT 2022 x86_64 x86_64 x86_64 GNU/Linux

Let’s check the boot loader folder.

[[email protected] ~]$ ls -ltrh /boot
total 516M
-rw-------. 1 root root 4.0M Jun  1  2021 System.map-4.18.0-305.3.1.el8.x86_64
-rw-r--r--. 1 root root 188K Jun  1  2021 config-4.18.0-305.3.1.el8.x86_64
-rwxr-xr-x. 1 root root 9.6M Jun  1  2021 vmlinuz-4.18.0-305.3.1.el8.x86_64
drwxr-xr-x. 3 root root   17 Jun  2  2021 efi
drwxr-xr-x. 3 root root   21 Jun  2  2021 loader
-rwxr-xr-x. 1 root root 9.6M Jun  2  2021 vmlinuz-0-rescue-40ec35b37a254049be3d85f9173b39a1
-rw-------. 1 root root  62M Jun  2  2021 initramfs-0-rescue-40ec35b37a254049be3d85f9173b39a1.img
drwxr-xr-x. 2 root root   39 Jun  2  2021 grub
-rw-------. 1 root root 4.2M May 12 03:21 System.map-4.18.0-372.9.1.el8.x86_64
-rw-r--r--. 1 root root 192K May 12 03:21 config-4.18.0-372.9.1.el8.x86_64
-rwxr-xr-x. 1 root root  10M May 12 03:21 vmlinuz-4.18.0-372.9.1.el8.x86_64
-rw-------. 1 root root 4.3M Jun  1 21:00 System.map-5.4.17-2136.307.3.6.el8uek.x86_64
-rw-r--r--. 1 root root 213K Jun  1 21:00 config-5.4.17-2136.307.3.6.el8uek.x86_64
-rwxr-xr-x. 1 root root  10M Jun  1 21:00 vmlinuz-5.4.17-2136.307.3.6.el8uek.x86_64
lrwxrwxrwx. 1 root root   57 Jun  8 08:35 symvers-5.4.17-2136.307.3.6.el8uek.x86_64.gz -> /lib/modules/5.4.17-2136.307.3.6.el8uek.x86_64/symvers.gz
-rw-------. 1 root root  86M Jun  8 08:36 initramfs-5.4.17-2136.307.3.6.el8uek.x86_64.img
-rwxr-xr-x. 1 root root  10M Jun  8 08:36 vmlinuz-0-rescue-ec2f03aecd97c5f99095ff2f3f63a155
-rw-------. 1 root root  86M Jun  8 08:37 initramfs-0-rescue-ec2f03aecd97c5f99095ff2f3f63a155.img
-rw-------. 1 root root  27M Jun  8 08:42 initramfs-4.18.0-305.3.1.el8.x86_64kdump.img
lrwxrwxrwx. 1 root root   49 Jun  8 08:42 symvers-4.18.0-372.9.1.el8.x86_64.gz -> /lib/modules/4.18.0-372.9.1.el8.x86_64/symvers.gz
-rw-------. 1 root root  87M Jun  8 08:44 initramfs-4.18.0-372.9.1.el8.x86_64.img
-rw-------. 1 root root  82M Jun  8 08:45 initramfs-4.18.0-305.3.1.el8.x86_64.img
-rw-------. 1 root root  27M Jun  8 11:22 initramfs-5.4.17-2136.307.3.6.el8uek.x86_64kdump.img
drwx------. 4 root root   83 Jun  8 11:25 grub2

And we can confirm that there is no CentOS base package installed on the system any more.

[[email protected] ~]$ rpm -qa | grep -i centos
[[email protected] ~]$

Conclusion

Switching CentOS 8 to Oracle Linux 8 was quite fast and simple. Of course, it might be more complicated on a production system having several other third party packages and softwares installed. Those package might need to certainly be reinstalled. The packages that install 3rd party kernel modules will for sure not work any more after switching, and would need to be reinstalled. Also the script only enables base repositories needed to switch to Oracle Linux. Before upgrading some packages, some additional repositories might need to be enabled first.