[GLLUG] Problems with CentOS 4 to 5 upgrade

[James Courtier-Dutton]

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
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