[GLLUG] Problems with CentOS 4 to 5 upgrade

[Imran Chaudhry]

Thanks for quick reply James.

I have had a similar response from the centos community forums.

I might have to just accept that it will be safer to jump straight to CentOS 7.

Do you happen to know if CentOS plan to make it easy to do major
dist-upgrades in future?


On 24 November 2017 at 08:16, James Courtier-Dutton
<james.dutton at gmail.com> wrote:
> Hi,
>
> I have experience upgrading CentOS 6 to Centos 7.
> It is very messy and in future I would never do it. I would reinstall from
> scratch straight to CentOS 7.
> CentOS is the same as Redhat with regards to upgrades.
> You can upgrade minor versions, but a new install for major versions.
> I.e. 6.1 -> 6.2 works, but 6.2 -> 7.1 does not.
>
> The reason is that the package versions are all messed up. After the upgrade
> from 6 to 7, the package manager still thought some of the 6 packages were
> more up to date than the same packages in 7.
> I have to go through identifying what they were and forcing an apparent
> downgrade on them to get them to 7.
>
> My advice to you would be install CentOS 7 on a test server and write
> migration tools for all the apps you need to transfer.
> I doubt you are actually using all 1500 apps that are installed.
>
> For example, to upgrade a mysql DB. Do a mysqldump. This writes everything
> out as SQL statements. You can then load that into a more up to date mysql
> server.
> We found that we had to rewrite some of our application because some
> behaviour of mysql has changed over time.
>
> For the upgrade I would advise going to CentOS 7. You should also consider
> Docker so that you can containerise the various applications. It makes
> upgrades a lot easier in future.
> You could also use VMs. One VM still at CentOS 4, and migrate one
> application at a time to CentOS 7.
> That way, you could move the ones that are easy to migrate first and then
> work on the harder ones in time.
>
> Kind regards
>
> James
>
>
>