Migrating from CentOS7 to RHEL7

There are various reasons why to migrate from CentOS to RHEL. Quicker access to bugfixes and new minor releases as well as having a fully commercially supported system.

There are different tutorial on the net how to migrate from RHEL to CentOS but almost no information about the other way round. It is quite simple and at the end of the day you have only Red Hat Packages installed.

In 2012 I wrote an article about Migrating from CentOS6 to RHEL6. Now its time for an update.

Disclaimer

Some of the procedures can be destructive for your system and/or your data. I’m not taking any responsibility for any damage casue. Take a full backup of your system before even thinking about trying this procedure!

Also import to note is that such a procedure is not supported by Redhat.

Requirements

There are only two things you need

• A valid RHEL subscription obtained from Redhats online store
• A RHEL7 ISO-Image which corresponds with your current CentOS minor release (or newer) which can be downloaded at Redhat downloads

Preparations

Be sure you activated your subscription.

Mount the ISO image on your CentOS7 machine:

[root@centos7 ~]# mount /dev/cdrom /mnt -o loop

Go to /mnt/Packages and install the packages we need:

[root@centos7 Packages]# yum -y localinstall subscription-manager-1.15.9-15.el7.x86_64.rpm

(Re)Move your CentOS repos
To avoid conflicts between CentOS and Redhat Repositories you need to get rid of them. Remove them or just keep a copy.

[root@centos7 Packages]# mkdir /etc/yum.repos.d.centos
[root@centos7 Packages]# mv /etc/yum.repos.d/CentOS-* /etc/yum.repos.d.centos

Force-remove the centos-release and yum RPMs

[root@centos7 Packages]# rpm -e yum --nodeps
[root@centos7 Packages]# rpm -ihv yum-3.4.3-132.el7.noarch.rpm
[root@centos7 Packages]# rpm -e centos-release --nodeps
[root@centos7 Packages]# yum localinstall redhat-release-server-7.2-9.el7.x86_64.rpm

Register your system

To get access to RHEL repositories, you need to register your system. The username “example@example.com” must be replaced with your username. The ID is a randomly generated UUID.

[root@centos7 ~]# subscription-manager register
Registering to: subscription.rhn.redhat.com:443/subscription
Username: example@example.com
Password: 
The system has been registered with ID: e61bd536-854c-4f32-a1fa-7f75c37046a5  
[root@centos7 ~]# 

Attach the system to a subscription

Usually it is just good enough to auto-attach the subscription needed.

[root@centos7 ~]# subscription-manager attach --auto


Installed Product Current Status:
Product Name: Red Hat Enterprise Linux Server
Status:       Subscribed

[root@centos7 ~]# s

Review enabled repositories

Sometimes you dont want to use all the repos provided. The simplest way is just to disable all and re-enable those you need.

[root@centos7 ~]# subscription-manager repos --list
[root@centos7 ~]# subscription-manager repos --disable "*"
[root@centos7 ~]# subscription-manager repos --enable rhel-7-server-rpms --enable rhel-7-server-optional-rpms --enable whatever-else-you-need
[root@centos7 ~]# yum clean all

Changing the Distribution

Now we have all requirements met, lets reinstall the packages.

[root@centos7 ~]# yum reinstall "*" --exclude=filesystem
[ommited output]
 zlib                     x86_64 1.2.7-15.el7           rhel-7-server-rpms  90 k
Not available:
 dhclient                 x86_64 12:4.2.5-42.el7.centos -                  0.0  
 plymouth                 x86_64 0.8.9-0.24.20140113.el7.centos
                                                        -                  0.0  
 curl                     x86_64 7.29.0-25.el7.centos   -                  0.0  
 grub2-tools              x86_64 1:2.02-0.29.el7.centos -                  0.0  
 basesystem               noarch 10.0-7.el7.centos      -                  0.0  
 plymouth-core-libs       x86_64 0.8.9-0.24.20140113.el7.centos
                                                        -                  0.0  
 mariadb-libs             x86_64 1:5.5.44-2.el7.centos  -                  0.0  
 libcurl                  x86_64 7.29.0-25.el7.centos   -                  0.0  
 dhcp-libs                x86_64 12:4.2.5-42.el7.centos -                  0.0  
 plymouth-scripts         x86_64 0.8.9-0.24.20140113.el7.centos
                                                        -                  0.0  
 dhcp-common              x86_64 12:4.2.5-42.el7.centos -                  0.0  
 grub2                    x86_64 1:2.02-0.29.el7.centos -                  0.0  
 centos-logos             noarch 70.0.6-3.el7.centos    -                  0.0  

Transaction Summary
=================================================================================
Reinstall      291 Packages
Not available   13 Packages

Total download size: 154 M
Installed size: 577 M
Is this ok [y/d/N]:

Here you can see the Centos specific packages, we need to take care about them later. Proceed and acknowledge with Y.

Cleanup

Now we need to manually clean up the CentOS specific packages with are named [package-name-and-version]-centos.

[root@centos7 ~]# rpm -qa --queryformat "%{NAME} %{VENDOR}\n" | grep -i centos | cut -d' ' -f1
filesystem
centos-logos
mariadb-libs
libcurl
dhcp-common
plymouth-scripts
dhclient
basesystem
plymouth-core-libs
curl
dhcp-libs
plymouth
[root@centos7 ~]#

With some of the packages you need to proceed very careful, the i.e. the filesystem package is awful. If you remove it, you will reinstall your system.

Luckily there is the rpm parameter –justdb which only does changes to the RPM-Database but not on the actual file system.

Some more critical packages need to be replaced as well.

[root@centos7 Packages]# rpm -e centos-logos plymouth plymouth-scripts plymouth-core-libs grub2 grub2-tools dhcp-common dhclient dhcp-libs curl libcurl --nodeps
[root@centos7 Packages]# rpm -i curl-7.29.0-25.el7.x86_64.rpm libcurl-7.29.0-25.el7.x86_64.rpm
[root@centos7 Packages]#  yum -y install plymouth plymouth-scripts plymouth-core-libs grub2 grub2-tools dhcp-common dhclient dhcp-libs
[root@centos7 ~]# yum remove basesystem
[root@centos7 ~]# yum -y install basesystem

Dirty Hardcore Hack, please be careful, use the –justdb parameter

[root@centos7 Packages]# rpm -e filesystem --nodeps --justdb
[root@centos7 Packages]# cp filesystem-3.2-20.el7.x86_64.rpm /root/
[root@centos7 Packages]# cd
[root@centos7 ~]# umount /mnt
[root@centos7 ~]# rpm -ihv filesystem-3.2-20.el7.x86_64.rpm 

Aftermath

Now update your system, reboot and check if all is working as expected. There may be more cleanup work to do.

[root@centos7 ~]# umount /mnt
[root@centos7 ~]# yum -y update && reboot

Check if there are still RPMs of vendor “Centos” installed:

[root@centos7 ~]# rpm -qa --queryformat "%{NAME} %{VENDOR}\n" | grep -i centos | cut -d' ' -f1

This should return nothing, almost all is now RHEL7. The only traces left are the previously install Kernels. They will get deleted over time when installing (updating) new Kernels.

In my case I just used CentOS7 minimal installation. The CentOS distribution comes with a total of 231 packages which need to be manually replaced if installed. If you plan to go down this road, please clone the system first for testing before migrating the actual system.

Support by Redhat

Will the converted machine be supported after this procedure? Well, officially it is not supported, but if there are no traces of CentOS left on the machine…

Better install RHEL in the first place 🙂