We have plans to port the application to RHEL5 ( currently it works on RHEL3). I would guess that the "C++", "C", ProCPP code would not need any (many) changes but there can be potential changes in the third party libraries used, eg Orbix, ILOG, Rogue Waves, Oracle, Xerces.
Does anyone have experience on a similar requirement and would share it with me. I am curious to know if we really have to make some drastic changes in compiler flags, way of compilation etc, when we switch to RHEL5, with respect ot the usage of the third party tools.
I can give the exact version of the libraries too if needed.
Missing information that someone needs, i can provide more info.
How smooth is such porting?

Please advise!

RHEL3 has a 2.4.x kernel whereas RHEL5 has 2.6.x so there are some significant differences even at kernel level.

There may be hardware you're currently running for which the drivers don't exist or are not automatically loaded so you may need extra work to get it working on your server. Presumably you wouldn't need to worry about it for the app you're shipping unless you're selling the hardware too.

Also there are other things e.g. reliance on udev for many things.

Also you have to be cognizant of 32 bit vs 64 bit. Are you porting your app to 64 bit?

I haven't done any porting but have seen a couple of things for apps originally written for 2.4 32 bit:

1) libstdc++ - Many folks that haven't ported require you to install compat-libstdc++-296 and/or an earlier one that I can't recall at the moment (note these are versions of package name but rather different compatibility libraries so the versions would be suffixed to them. There are other compatibility libraries but these are the ones I've needed most often. You may wish to insure you've set your software up to not require that or at least note that you do.

2) Because RHEL4 could be run in 32 bit mode it may be RHEL5 can be as well (have done former but not latter). If so there may be some need for investigating how you're going to do this (or tell users it is not supported). Look into linux32 information for more details - I've only seen it from the runtime method of Oracle E-Business.

Your another options is don't do porting at all.

You can use Ermine (http://magicErmine.com) or statifier (http://statifier.sf.net) to pack your applications on the RHEL3 box.
Once packed, them able to run nearly on any distro, without need to install
any libraries. And if application packed on i386 it can also run on x86_64 without 32-bit compatibility libs installed.

Valery.