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Possible Duplicate:
Caveats when upgrading from Java 6 to Java 7 on hundreds of production servers

I am about to upgrade the RHEL version from RHEL 5.4 to RHEL 6.3 in a few hundreds of production servers.

The upgrade will be tested on a staging environment on virtual machines before production deployment.

Are there any backward-compatibility issues with RHEL upgrades?

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marked as duplicate by jscott, Sven, Alex, Dave M, Michael Hampton Feb 1 '13 at 5:50

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Are you performing in-place upgrades? If so, please see: Why is it so difficult to upgrade between major versions of Red Hat and CentOS? – ewwhite Jan 30 '13 at 14:01
It's not in-place. The server is re-installed, and the existing software packages - in-house and external open source tools - are installed on the new operating system, so I guess my main concern is software package compatibility. – Adam Matan Jan 30 '13 at 14:10
@AdamMatan This is your environment, so you'll have to test the software side. I've given some general advice about basic differences, though. – ewwhite Jan 30 '13 at 14:17
up vote 5 down vote accepted

I wouldn't run the upgrade process this way if you're planning to perform in-place transitions from EL5 to EL6. It's not an easy or clean process.

See: Why is it so difficult to upgrade between major versions of Red Hat and CentOS? and Upgrade CentOS 5.x to CentOS 6.x - tips and techniques

However, you have the right idea of testing this in a limited-capacity first.

Regardless of deployment technique, the biggest issues I saw in moving from EL5 to EL6 were:

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