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We have quite a few customers still running on CentOS 8 and you probably already are aware that CentOS 8 will be end of life by the end of this year. This forces a lot of companies to either switch to an alternative or to stick with CentOS stream. For most enterprise workloads CentOS stream is not a solution as it is rolling release, and if you want to keep a Red Hat compatible enterprise distribution there are the following alternatives:

In this post we’ll look into how you can switch from CentOS 8 to Red Hat 8, as this is what we’re doing for one of our customers currently.

I did a fresh installation of CentOS 8 which brings me to this release:

[[email protected] ~]$ cat /etc/centos-release
CentOS Linux release 8.5.2111

If you check the compatibility matrix in the official documentation you’ll find this:

Switching from CentOS 8.5 to Red Hat 8.5 seems not to be supported but as I do not want to downgrade we’ll try anyway. As Red Hat 8.5 was just released some days ago, I guess the documentation was not yet updated. For production systems, make sure that you check all prerequisites before you start.

The first step is to install the conversion tool:

[[email protected] ~]$ curl -o /etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release https://www.redhat.com/security/data/fd431d51.txt
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  1855  100  1855    0     0   3644      0 --:--:-- --:--:-- --:--:--  3644
[[email protected] ~]$ curl --create-dirs -o /etc/rhsm/ca/redhat-uep.pem https://ftp.redhat.com/redhat/convert2rhel/redhat-uep.pem
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  7411  100  7411    0     0   4927      0  0:00:01  0:00:01 --:--:--  4924
[[email protected] ~]$ curl -o /etc/yum.repos.d/convert2rhel.repo https://ftp.redhat.com/redhat/convert2rhel/8/convert2rhel.repo
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   247  100   247    0     0    164      0  0:00:01  0:00:01 --:--:--   164

This creates a new yum/dnf repository definition:

[[email protected] ~]$ cat /etc/yum.repos.d/convert2rhel.repo
[convert2rhel-for-rhel-8-rpms]
name=Convert2RHEL for OS 8
baseurl=https://cdn.redhat.com/content/public/convert2rhel/8/x86_64/os/
enabled=1
gpgcheck=1
sslcacert=/etc/rhsm/ca/redhat-uep.pem
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release

… and now the conversion tool can be installed:

[[email protected] ~]$ yum -y install convert2rhel
Convert2RHEL for OS 8                                                                                                                                                                                                                         6.5 kB/s | 3.9 kB     00:00    
Dependencies resolved.
==============================================================================================================================================================================================================================================================================
 Package                                                  Architecture                                       Version                                                                           Repository                                                                Size
==============================================================================================================================================================================================================================================================================
Installing:
 convert2rhel                                             noarch                                             0.24-2.el8                                                                        convert2rhel-for-rhel-8-rpms                                             130 k
Installing dependencies:
 python3-pip                                              noarch                                             9.0.3-20.el8                                                                      appstream                                                                 20 k
 python36                                                 x86_64                                             3.6.8-38.module_el8.5.0+895+a459eca8                                              appstream                                                                 19 k
 yum-utils                                                noarch                                             4.0.21-3.el8                                                                      baseos                                                                    73 k
Enabling module streams:
 python36                                                                                                    3.6                                                                                                                                                             

Transaction Summary
==============================================================================================================================================================================================================================================================================
Install  4 Packages

Total download size: 242 k
Installed size: 413 k
Downloading Packages:
(1/4): python36-3.6.8-38.module_el8.5.0+895+a459eca8.x86_64.rpm                                                                                                                                                                               125 kB/s |  19 kB     00:00    
(2/4): yum-utils-4.0.21-3.el8.noarch.rpm                                                                                                                                                                                                      431 kB/s |  73 kB     00:00    
(3/4): python3-pip-9.0.3-20.el8.noarch.rpm                                                                                                                                                                                                    107 kB/s |  20 kB     00:00    
(4/4): convert2rhel-0.24-2.el8.noarch.rpm                                                                                                                                                                                                     440 kB/s | 130 kB     00:00    
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                                                                                                                                         217 kB/s | 242 kB     00:01     
CentOS Linux 8 - AppStream                                                                                                                                                                                                                    1.6 MB/s | 1.6 kB     00:00    
Importing GPG key 0x8483C65D:
 Userid     : "CentOS (CentOS Official Signing Key) "
 Fingerprint: 99DB 70FA E1D7 CE22 7FB6 4882 05B5 55B3 8483 C65D
 From       : /etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial
Key imported successfully
Convert2RHEL for OS 8                                                                                                                                                                                                                         1.8 MB/s | 1.8 kB     00:00    
Importing GPG key 0xFD431D51:
 Userid     : "Red Hat, Inc. (release key 2) "
 Fingerprint: 567E 347A D004 4ADE 55BA 8A5F 199E 2F91 FD43 1D51
 From       : /etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
Key imported successfully
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                                                                                                                                                                                                                      1/1 
  Installing       : python36-3.6.8-38.module_el8.5.0+895+a459eca8.x86_64                                                                                                                                                                                                 1/4 
  Running scriptlet: python36-3.6.8-38.module_el8.5.0+895+a459eca8.x86_64                                                                                                                                                                                                 1/4 
  Installing       : python3-pip-9.0.3-20.el8.noarch                                                                                                                                                                                                                      2/4 
  Installing       : yum-utils-4.0.21-3.el8.noarch                                                                                                                                                                                                                        3/4 
  Installing       : convert2rhel-0.24-2.el8.noarch                                                                                                                                                                                                                       4/4 
  Running scriptlet: convert2rhel-0.24-2.el8.noarch                                                                                                                                                                                                                       4/4 
  Verifying        : python3-pip-9.0.3-20.el8.noarch                                                                                                                                                                                                                      1/4 
  Verifying        : python36-3.6.8-38.module_el8.5.0+895+a459eca8.x86_64                                                                                                                                                                                                 2/4 
  Verifying        : yum-utils-4.0.21-3.el8.noarch                                                                                                                                                                                                                        3/4 
  Verifying        : convert2rhel-0.24-2.el8.noarch                                                                                                                                                                                                                       4/4 

Installed:
  convert2rhel-0.24-2.el8.noarch                               python3-pip-9.0.3-20.el8.noarch                               python36-3.6.8-38.module_el8.5.0+895+a459eca8.x86_64                               yum-utils-4.0.21-3.el8.noarch                              

Complete!

For actually converting the system to Red Hat Enterprise Linux you need access to the Red Hat portal and an active subscription you can attach to the system:

[[email protected] ~]$ convert2rhel --username [username] --password [password]

The first output you’ll see is the license agreement:

[11/18/2021 03:22:53] TASK - [Prepare: Show Red Hat software EULA] ******************************
The following text is a copy of the November 18, 2019 version of Red Hat GPLv2-Based End User License Agreement (EULA) [1].
For up-to-date version of the EULA, visit [2].
[1] https://www.redhat.com/licenses/Red_Hat_GPLv2-Based_EULA_20191118.pdf
[2] https://www.redhat.com/en/about/agreements

END USER LICENSE AGREEMENT
RED HAT GPLv2-BASED
...

Before you proceed, make sure that all the checks/tasks are successful, e.g.:

[11/18/2021 03:23:16] TASK - [Prepare: Checking the firmware interface type (BIOS/UEFI)] ********
BIOS detected.

[11/18/2021 03:23:16] TASK - [Prepare: Checking /mnt and /sys are read-write] *******************
Read-only /mnt or /sys mount points not detected.

[11/18/2021 03:23:16] TASK - [Prepare: Check kernel compatibility with RHEL] ********************
Kernel is compatible with RHEL

[11/18/2021 03:23:16] TASK - [Prepare: Checking if --enablerepo repositories are accessible] ****
Skipping the check of repositories due to the use of RHSM for the conversion.

Also note the packages that will be removed, maybe you need to re-install them after the conversion:

WARNING - The following packages will be removed...
Package                               Vendor/Packager  Repository
-------                               ---------------  ----------
centos-logos-85.8-2.el8.x86_64        CentOS           @baseos
centos-logos-httpd-85.8-2.el8.noarch  CentOS           @baseos
centos-gpg-keys-8-3.el8.noarch        CentOS           @baseos

Once you are sure to proceed:

Continue with the system conversion? [y/n]: y

Backing up centos-logos-85.8-2.el8.x86_64
Successfully downloaded the centos-logos-85.8-2.el8.x86_64 package.
Backing up centos-logos-httpd-85.8-2.el8.noarch
Successfully downloaded the centos-logos-httpd-85.8-2.el8.noarch package.
Backing up centos-gpg-keys-8-3.el8.noarch
Successfully downloaded the centos-gpg-keys-8-3.el8.noarch package.
Removing package: centos-logos-85.8-2.el8.x86_64
Removing package: centos-logos-httpd-85.8-2.el8.noarch
Removing package: centos-gpg-keys-8-3.el8.noarch
...

Again, double check that all the tasks/checks are fine, e.g.:

[11/18/2021 03:26:15] TASK - [Convert: Resolve possible edge cases] *****************************
Checking if java-1.7.0-openjdk is installed.
java-1.7.0-openjdk not installed.
Removing shim-x64 package yum protection.
Relevant to Oracle Linux 7 only. Skipping.

[11/18/2021 03:26:15] TASK - [Convert: Subscription Manager - Download packages] ****************
Successfully downloaded the subscription-manager package.
Successfully downloaded the subscription-manager-rhsm-certificates package.
Successfully downloaded the python3-subscription-manager-rhsm package.
Successfully downloaded the dnf-plugin-subscription-manager package.
Successfully downloaded the python3-syspurpose package.
...

Finally select the subscription you want to attach to the system:

Enter number of the chosen subscription: 11

Attaching subscription with pool ID xxxx to the system ...
Successfully attached a subscription for: Red Hat Enterprise Linux, Standard Support (128 Sockets, NFR, Partner Only)

[11/18/2021 03:30:42] TASK - [Convert: Get RHEL repository IDs] *********************************
RHEL repository IDs to enable: rhel-8-for-x86_64-baseos-rpms, rhel-8-for-x86_64-appstream-rpms

[11/18/2021 03:30:42] TASK - [Convert: Subscription Manager - Check required repositories] ******
Verifying needed RHEL repositories are available ... 
Repositories available through RHSM:
...
Needed RHEL repos are available.

[11/18/2021 03:31:13] TASK - [Convert: Subscription Manager - Disable all repositories] *********
Repositories disabled.

[11/18/2021 03:31:58] TASK - [Convert: Remove packages containing repofiles] ********************
Searching for packages containing repofiles or affecting variables in the repofiles:

centos-release* ................................. 0
centos-repos .................................... 0
centos-linux-repos .............................. 1
centos-stream-repos ............................. 0
centos-linux-release ............................ 1
centos-stream-release ........................... 0


WARNING - The following packages will be removed...
Package                                     Vendor/Packager  Repository
-------                                     ---------------  ----------
centos-linux-repos-8-3.el8.noarch           CentOS           @baseos
centos-linux-release-8.5-1.2111.el8.noarch  CentOS           @baseos


Continue with the system conversion? [y/n]: y


Backing up centos-linux-repos-8-3.el8.noarch
Successfully downloaded the centos-linux-repos-8-3.el8.noarch package.
Backing up centos-linux-release-8.5-1.2111.el8.noarch
Successfully downloaded the centos-linux-release-8.5-1.2111.el8.noarch package.
Removing package: centos-linux-repos-8-3.el8.noarch
Removing package: centos-linux-release-8.5-1.2111.el8.noarch

[11/18/2021 03:33:20] TASK - [Convert: Subscription Manager - Enable RHEL repositories] *********
Repositories enabled through subscription-manager

[11/18/2021 03:33:58] TASK - [Convert: Final system checks before main conversion] **************
Comparing the loaded kernel modules with the modules available in the following RHEL kernel packages available in the enabled repositories:
 kernel-core-0:4.18.0-348.2.1.el8_5.x86_64
 kernel-debug-core-0:4.18.0-348.2.1.el8_5.x86_64
 kernel-debug-modules-0:4.18.0-348.2.1.el8_5.x86_64
 kernel-debug-modules-extra-0:4.18.0-348.2.1.el8_5.x86_64
 kernel-modules-0:4.18.0-348.2.1.el8_5.x86_64
 kernel-modules-extra-0:4.18.0-348.2.1.el8_5.x86_64
 kmod-kvdo-0:6.2.5.72-81.el8.x86_64
 kmod-redhat-atlantic-0:4.18.0_255.el8_dup8.3-1.el8_3.x86_64
 kmod-redhat-bnxt_en-0:1.10.0_dup8.1-2.el8_1.x86_64
 kmod-redhat-btusb-0:0.8_4.18.0_80.23_dup8.0-4.el8_0.x86_64
 kmod-redhat-ice-0:0.8.2_k_dup8.2-1.el8_2.x86_64
 kmod-redhat-ionic-0:4.18.0.210_dup8.2-2.el8_2.x86_64
 kmod-redhat-iwlwifi-0:4.18.0_107_dup8.0-5.el8_0.x86_64
 kmod-redhat-mlx5_core-0:5.0_0_dup8.2-2.el8_2.x86_64
 kmod-redhat-mpt3sas-0:35.101.00.00_dup8.3-1.el8_3.x86_64
 kmod-redhat-oracleasm-8:2.0.8-12.el8.x86_64
 kmod-redhat-oracleasm-kernel_4_18_0_240-8:2.0.8-1.3.el8_3.x86_64
 kmod-redhat-oracleasm-kernel_4_18_0_240_14_1-8:2.0.8-1.3.el8_3.x86_64
WARNING - ********************************************************
WARNING - The tool allows rollback of any action until this point.
WARNING - By continuing all further changes on the system will need to be reverted manually by the user, if necessary.
WARNING - ********************************************************

Continue with the system conversion? [y/n]: 

Up until now you can rollback any changes, so please check all the output carefully before you continue from here. The following step will take some time as a lot of packages will be updated/replaced:

Continue with the system conversion? [y/n]: y



[11/18/2021 03:36:16] TASK - [Convert: Import Red Hat GPG keys] *********************************
GPG keys imported.
GPG keys imported.

[11/18/2021 03:36:16] TASK - [Convert: Prepare kernel] ******************************************
Installing RHEL kernel ...
Updating Subscription Management repositories.
Last metadata expiration check: 0:02:03 ago on Thu Nov 18 03:34:16 2021.
Package kernel-4.18.0-348.2.1.el8_5.x86_64 is already installed.
Dependencies resolved.
Nothing to do.
Complete!

Conflict of kernels: One of the installed kernels has the same version as the latest RHEL kernel.
Updating Subscription Management repositories.
Last metadata expiration check: 0:02:12 ago on Thu Nov 18 03:34:16 2021.
Dependencies resolved.
================================================================================
 Package         Arch    Version           Repository                      Size
================================================================================
Installing:
 kernel          x86_64  4.18.0-348.el8    rhel-8-for-x86_64-baseos-rpms  7.0 M
Installing dependencies:
 kernel-core     x86_64  4.18.0-348.el8    rhel-8-for-x86_64-baseos-rpms   38 M
 kernel-modules  x86_64  4.18.0-348.el8    rhel-8-for-x86_64-baseos-rpms   30 M
...
[11/18/2021 03:39:56] TASK - [Convert: Replace packages] ****************************************
Performing update of the CentOS Linux packages ...
Updating Subscription Management repositories.
Last metadata expiration check: 0:05:46 ago on Thu Nov 18 03:34:16 2021.
Dependencies resolved.
========================================================================================================================
 Package                       Arch    Version                                   Repository                         Size
========================================================================================================================
Upgrading:
 buildah                       x86_64  1.22.3-2.module+el8.5.0+12582+56d94c81    rhel-8-for-x86_64-appstream-rpms  7.7 M
 cockpit-podman                noarch  33-1.module+el8.5.0+12582+56d94c81        rhel-8-for-x86_64-appstream-rpms  437 k
 conmon                        x86_64  2:2.0.29-1.module+el8.5.0+12582+56d94c81  rhel-8-for-x86_64-appstream-rpms   52 k
 container-selinux             noarch  2:2.167.0-1.module+el8.5.0+12582+56d94c81 rhel-8-for-x86_64-appstream-rpms   54 k
 containernetworking-plugins   x86_64  1.0.0-1.module+el8.5.0+12582+56d94c81     rhel-8-for-x86_64-appstream-rpms   19 M
 containers-common             noarch  2:1-2.module+el8.5.0+12582+56d94c81       rhel-8-for-x86_64-appstream-rpms   77 k
 criu                          x86_64  3.15-3.module+el8.5.0+12582+56d94c81      rhel-8-for-x86_64-appstream-rpms  518 k
...
Performing reinstallation of the CentOS Linux packages ...
Updating Subscription Management repositories.
Last metadata expiration check: 0:06:46 ago on Thu Nov 18 03:34:16 2021.
Dependencies resolved.
=========================================================================================================================
 Package                                Arch    Version                           Repository                         Size
=========================================================================================================================
Reinstalling:
 NetworkManager                         x86_64  1:1.32.10-4.el8                   rhel-8-for-x86_64-baseos-rpms     2.6 M
 NetworkManager-config-server           noarch  1:1.32.10-4.el8                   rhel-8-for-x86_64-baseos-rpms     131 k
 NetworkManager-libnm                   x86_64  1:1.32.10-4.el8                   rhel-8-for-x86_64-baseos-rpms     1.8 M
 NetworkManager-libreswan               x86_64  1.2.10-4.el8                      rhel-8-for-x86_64-appstream-rpms  120 k
 NetworkManager-team                    x86_64  1:1.32.10-4.el8                   rhel-8-for-x86_64-baseos-rpms     149 k
 NetworkManager-tui                     x86_64  1:1.32.10-4.el8                   rhel-8-for-x86_64-baseos-rpms     336 k
 PackageKit                             x86_64  1.1.12-6.el8                      rhel-8-for-x86_64-appstream-rpms  599 k
 PackageKit-glib                        x86_64  1.1.12-6.el8                      rhel-8-for-x86_64-appstream-rpms  140 k
 abattis-cantarell-fonts                noarch  0.0.25-6.el8                      rhel-8-for-x86_64-appstream-rpms  156 k
...
Dependencies resolved.
Nothing to do.
Complete!
Received return code: 0


[11/18/2021 03:52:35] TASK - [Convert: List remaining non-Red Hat packages] *********************
Listing packages not signed by Red Hat
All packages are now signed by Red Hat.

[11/18/2021 03:52:37] TASK - [Convert: Configure the bootloader] ********************************
BIOS detected. Nothing to do.

[11/18/2021 03:52:37] TASK - [Convert: Patch yum configuration file] ****************************
Skipping patching, yum configuration file not modified

[11/18/2021 03:52:37] TASK - [Final: rpm files modified by the conversion] **********************
Running the 'rpm -Va' command which can take several minutes. It can be disabled by using the --no-rpm-va option.

Running the 'rpm -Va' command which can take several minutes. It can be disabled by using the --no-rpm-va option.
The 'rpm -Va' output has been stored in the /var/log/convert2rhel/rpm_va_after_conversion.log file
Comparison of modified rpm files from before and after the conversion:
--- /var/log/convert2rhel/rpm_va.log
+++ /var/log/convert2rhel/rpm_va_after_conversion.log
@@ -0,0 +1,2 @@
+....L....  c /etc/nsswitch.conf
+.M.......  g /var/lib/plymouth/boot-duration
@@ -2,2 +3,0 @@
-.M.......  g /var/lib/plymouth/boot-duration
-....L....  c /etc/nsswitch.conf
@@ -9,2 +8,0 @@
-.......T.  c /etc/selinux/targeted/contexts/customizable_types
-.......T.    /etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release

[11/18/2021 03:53:03] TASK - [Final: Remove temporary folder /var/lib/convert2rhel/] ************
Temporary folder /var/lib/convert2rhel/ removed

Conversion successful!

WARNING - In order to boot the RHEL kernel, restart of the system is needed.

Time to reboot and check if all is fine:

[[email protected] ~]$ systemctl reboot
[[email protected] ~]$ Connection to 192.168.100.243 closed by remote host.
Connection to 192.168.100.243 closed.
[email protected]:~$ ssh [email protected]
[email protected]'s password: 
Activate the web console with: systemctl enable --now cockpit.socket

Last login: Thu Nov 18 02:38:37 2021 from 192.168.100.1
[[email protected] ~]$ cat /etc/os-release 
NAME="Red Hat Enterprise Linux"
VERSION="8.5 (Ootpa)"
ID="rhel"
ID_LIKE="fedora"
VERSION_ID="8.5"
PLATFORM_ID="platform:el8"
PRETTY_NAME="Red Hat Enterprise Linux 8.5 (Ootpa)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:redhat:enterprise_linux:8::baseos"
HOME_URL="https://www.redhat.com/"
DOCUMENTATION_URL="https://access.redhat.com/documentation/red_hat_enterprise_linux/8/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"

REDHAT_BUGZILLA_PRODUCT="Red Hat Enterprise Linux 8"
REDHAT_BUGZILLA_PRODUCT_VERSION=8.5
REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux"
REDHAT_SUPPORT_PRODUCT_VERSION="8.5"

[[email protected] ~]$ dnf repolist
Updating Subscription Management repositories.
repo id                                                                                                                    repo name
convert2rhel-for-rhel-8-rpms                                                                                               Convert2RHEL for OS 8
rhel-8-for-x86_64-appstream-rpms                                                                                           Red Hat Enterprise Linux 8 for x86_64 - AppStream (RPMs)
rhel-8-for-x86_64-baseos-rpms                                                                                              Red Hat Enterprise Linux 8 for x86_64 - BaseOS (RPMs)

[[email protected] ~]$ dnf update -y
Updating Subscription Management repositories.
Red Hat Enterprise Linux 8 for x86_64 - BaseOS (RPMs)                                                                                                                                                                                         3.9 MB/s |  41 MB     00:10    
Red Hat Enterprise Linux 8 for x86_64 - AppStream (RPMs)                                                                                                                                                                                      4.1 MB/s |  37 MB     00:09    
Last metadata expiration check: 0:00:03 ago on Thu 18 Nov 2021 03:55:39 AM EST.
Dependencies resolved.
Nothing to do.
Complete!

Looks good. In real live it might be more complicated, depending on what is installed on the original system.

2 Comments

  • Simon says:

    Thanks – first system I tried this on had perl-common-sense installed, and the upgrade fell over badly after passing the point of no return because it couldn’t work out what to do with that package. It just got to a point and said “can’t resolve yum issue”, and stopped. At that point the system was unbootable and basically broken. I restored the system from backup (it’s a virtual), removed perl-common-sense, tried again – it worked fine. I enabled RH codeready repo, reinstalled perl-common-sense, and rebooted. All good.
    On a web server, worked fine all the way through no issues.
    Thanks for the clear steps.

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Daniel Westermann
Daniel Westermann

Principal Consultant & Technology Leader Open Infrastructure