How to upgrade CentOS 6 to CentOS 7

This article comes with a HUGE warning. This was written using beta tools available from here: http://dev.centos.org/centos/6/upg/x86_64/Packages/

I will likely update this article when these tools are no longer in beta and when I perform this on my more complicated production server. Right now I’m testing these packages and this method on a relatively simple CentOS 6 test server I have at work.

My test server has the basics on it like Apache, PHP, NFS, VNC, Samba and Gnome. It is a vSphere VM with 2vCPUs, 4GB of RAM and the storage is back ended on a NetApp via NFS.

I pieced this together using the references at the bottom of the post. This will probably work for upgrading RHEL6 to RHEL7 as well but you’ll need to figure out the mirror information. I don’t have access to RHEL repos.

 

TAKE A FULL SYSTEM BACKUP BEFORE FOLLOWING THIS GUIDE

  1.  Download the upgrade packages from http://dev.centos.org/centos/6/upg/x86_64/Packages/

  2. Install the tools. My server needed some pre-reqs which yum took care of
  3. Run the upgrade tool
  4. The tool will now warn you that you should have taken a full system backup. Hopefully you did. Press ‘y’ to contiune
  5. The tool will now run a bunch of tests to determine if there are any blockers for an upgrade. This took about 10 minutes on my system. Once the tool completes it’s assessment you’ll find an upgrade report in ‘/root/preupgrade-results/’
  6. Review the files in the report. Mine came out with no results…. I take this to mean it found nothing wrong with an in place upgrade…. or there is a bug in the tools. The readme included this description of each file and status descriptions:

     
  7. Since my report didn’t lead me to believe there were any issues that had to be dealt with pre-upgrade I went for it. First I had to import the repo key and then I ran the upgrade

    Note: I had to add “–force” to the above command. It kept telling me I had not run ‘preupg’ which I had”
  8. After running the above command things started happening. From what I’ve read online this process will take up to 90 minutes while it downloads updates, creates a new boot image, reboots the server and performs the upgrade. The system will automatically reboot when it’s ready.On my system spec’d out as I listed above on a 300mbit internet connection the upgrade process took about 45 minutes.

That’s it! After a few reboots I ended up with a CentOS 7 machine…. with a few issues.

In my case Gnome would load a black screen and there were about 164 CentOS 6 packages left that were not upgraded to their equivalent CentOS 7 packages which caused ‘yum update’ to not work anymore citing dependency issues.

I also had a package, pywebkitgtk, which I had installed that was causing ‘yum update’ to not function properly after adding the EPEL Beta 7 Repo. A quick ‘yum remove pywebkitgtk’ and then ‘yum update’ fixed that.

Apache wasn’t very happy either. The config file needed a lot of work.

On my server there ended up being about 134 CentOS6 packages left over which may or may not cause conflicts in the future.

While this technically worked I’m going to recommend side-by-side upgrades to a fresh CentOS 7 server as the better way to do this. I also believe it is the recommended best practice.

 

References

How to convert RHEL 6.x to CentOS 6.x

Last modified: [last-modified]

This post relates to my older post about converting RHEL 5.x to CentOS 5.x. All the reasons for doing so and other background information can be found in that post.

This post will cover how to convert RHEL 6.x to 5.x.

Updated 2016-03-29 – Thanks to feedback from here I’ve updated the guide.

Updates and Backups!

  1. Fully patch your system and reboot your system before starting this process
  2. Take a full backup of your system or a Snapshot if it’s a VM

Conversion

  1. Login to the server and become root
  2. Clean up yum’s cache
  3. Create a temporary working area
  4. Determine your version of RHEL
  5. Determine your architecture (32-bit = i386, 64-bit = x86_64)
  6. Download the applicable files for your release and architecture. The version numbers on these packages could change. To find the current versions of these files browse this FTP site: http://mirror.centos.org/centos/6/os/i386/Packages/ (32-bit) or http://mirror.centos.org/centos/6/os/x86_64/Packages/ (64-bit) and replace the ‘x’ values below with the current version numbers
    CentOS 6.5 / 32-bit

    CentOS 6.5 / 64-bit
  7. Import the GPG key for the appropriate version of CentOS
  8. Remove RHEL packages

    Note:
    If the ‘rpm -e’ command fails saying one of the packages is not installed remove the package from the command and run it again.
  9. Remove any left over RHEL subscription information and the subscription-manager

    Note:
    If you do not do this every time you run ‘yum’ you will receive the following message: “This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.”
  10. Force install the CentOS RPMs we downloaded
  11. Clean up yum one more time and then upgrade
  12. Reboot your server
  13. Verify functionality
  14. Delete VM Snapshot if you took one as part of the backup

 

References