How does the CentOS numbering work?

Major releases are 'before the dot', eg 5.x and 6.x as far as I see, and minor changes after that.


  1. If I do a yum update on a 6.1 system, will it update to 6.current?
  2. Is it possible to safely upgrade from 6.x to 6.y via yum update?
  3. Is it possible to safely upgrade from 5.x to 6.x via yum update?
  4. What do the parts 'mean'?
  5. Are kernel updates on the left part? Or also on the right part?
  6. Would there be a reason and a way to keep the OS 'locked' on 6.1?

These are probably very basic questions but I just can't seem to find a good answer.

  1. Yes, by default a yum update does an update to the latest minor version and kernel version.
  2. Depends on what "safely" means to you. Some updates affect packages that might be necessary for your apps to run correctly. You should always research what the updates on your system will modify, ALWAYS BACKUP so you can revert, and try on a test environment first if possible.
  3. In-place upgrade is not supported across major releases. That being said, if you are a risky person, you can always take a chance with something like this http://www.linuxquestions.org/questions/blog/iamswift-664867/in-place-upgrade-from-rhel-5-x-to-rhel-6-x-34929/
  4. In CentOS the 'parts' are taken from the RHEL releases. In RHEL/CentOS versioning goes quite related to a) major kernel update for major version and b) important bugs/fixes/milestones for minor versioning.
  5. Major version changes do normally reflect kernel major versions for the left part, and normally minor version do include minor kernel changes. You can check the version table and see for yourself in here: http://en.wikipedia.org/wiki/CentOS#Versioning
  6. Yes, you might need keep a version or controlling tightly the modified packages, specially if you are using your own developed software or, as they already said, you have some software installed and the vendor only supports certain versions.
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My answers are: It depends.

  1. Yes.
  2. Not to arbitrary versions; it will always update to the latest version. But safe: Yes.
  3. It might work, but most people discourage that. I wouldn't do that myself. Better reinstall.
  4. The first part - 5 or 6 - is the major release version, the second part the minor release version.
  5. Kernel updates may happen at any time, even while doing yum update in 6.4, although no newer minor version is available.
  6. Yes, if you are using proprietary software which is only released for this very version of RHEL. I have this situation quite often; the vendor will only give support if a certain major/minor version of RHEL is used. Point is, since RHEL 6, you basically will lose the ability to get security updates; yum update will always update to the latest minor version available for this major release.
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  • Thanks. I added one question, maybe you can look at that? :) – Karlo Mar 20 '13 at 15:08
  1. yes
  2. yes it is safe
  3. no, it is not supported, but possible. Not recommended.
  4. Major version and minor version. They are arbitrarily chosen by RedHat.
  5. The kernel updates are done in both minor and major version
  6. No, you should upgrade to the latest minor version as long as is supported by RedHat, then install a new server with the latest version. The only reason to freeze is if you want to replicate another "frozen" system, or non technical reasons - like your boss does not want to install the security upgrades.

You should always plan how to do the upgrades and have recent full backups close to you. If you are using VMs, then make a VM snapshot before upgrade and remove the snapshot after a few weeks.

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