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I have a machine running a legacy J2EE application. The code is not Maven-ized and it works with pretty old Java and Postgres versions. I have converted it to a VM in ESXI and I'd like to try to upgrade it to a modern, binary-compatible version of RHEL (Centos or Scientific LInux) and see if things would still work.

Where should I start? Am I being too optimistic with this one?

It's more of an experiment and I'm not doing it on a production machine. But given the OS is pretty old I am looking for a way to do this eventually.

Many thanks

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☠☠ Do not attempt to upgrade across major versions of EL. ☠☠

The CentOS wiki has a guide to migrate from RHEL to CentOS. The procedure for EL3 should be similar to that of EL5.

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Here's a quick test. Is your RHEL 3.x server running a 64-bit version? Do you want the new OS to be 64-bit (you should). While there are convoluted ways to perform in-place upgrades between rpm-based OS releases, if there's an architecture difference (e.g. 32-bit to 64-bit), an in-place upgrade is just not possible.

Your best bet, especially with the existence of a virtual environment, is to build a new VM containing the target operating system and migrate the data. You'll have to pg_dump and reimport the Postgres database and install the appropriate versions of Java.

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