Upgrade RHEL3 to RHEL4, upgrade or clean install?

[nilesh vaghela]

Even Redhat preferred to go for clean upgrad.

May be help ful to you.

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Issue: How do I migrate to Red Hat Enterprise Linux version 4 from version
3?
Resolution:

If you have an active Red Hat Enterprise Linux subscription, you can migrate
your system at no additional cost.
Best Choice: Administrator-Guided Migration

The safest method to migrate from an earlier Red Hat release is an
administrator-guided migration. In this migration method, the system
administrator:

   - Evaluates the currently deployed system
   - Backs up the deployed configuration data, user data, and software
   applications to an external system
   - Performs a fresh install of Red Hat Enterprise Linux 4
   - Restores the required configuration data, user data, and software
   applications

Red Hat officially supports administrator guided migrations for commercial
deployments, as this method provides the highest probability of a successful
migration.

*WARNING:* Use of the "upgrade" option during the installation process can
cause erratic system behavior in various cases and is unsupported by Red
Hat. If you experience problems with an upgraded system and are seeking
assistance from Red Hat Support, you will be instructed to perform a clean
installation.
Second Choice: Automated Migration (not recommended)

Red Hat Enterprise Linux 4 also includes support for automated migrations
from earlier Red Hat Enterprise Linux releases. An automated migration is
implemented by Anaconda, the Red Hat Enterprise Linux 4 installer. Red Hat
does not recommend an automated migration, as it provides a lower
probability of success than do administrator-guided migrations. Red Hat
technical support provides assistance only with automated migrations from
the most recent previous release of Red Hat Enterprise Linux. The Red Hat
Enterprise Linux 4 installer warns you about upgrading from any release
earlier than Red Hat Enterprise Linux 3, but still allows you to proceed at
your discretion.

Red Hat Enterprise Linux 4 avoids incomplete migrations. The Red Hat
Enterprise Linux automated upgrade capability handles only the upgrade of
system components distributed with the Red Hat Enterprise Linux base
operating system. Automated upgrades may impact non-standards-conforming
third-party applications in unspecified ways, some of which may not be found
until you run the application. By establishing a clean baseline and then
reinstalling third-party applications using their native installation tool
on a fresh system, application-install time-dependency checking can be
employed to ensure that a complete runtime environment is available for all
third-party software.

For more information on upgrading to Red Hat Enterprise Linux 4, refer to
the following document:
http://www.redhat.com/f/pdf/rhel4/UpgradeGuidelines.pdf


Nilesh