Hi,

Is it possible to upgrade Red Hat Linux 2.1 AS to Red Hat ES 4.0.

Regards,

Manoj

RHEL 2.1 is really old and has a 2.4 kernel. RHEL4 (& 5) have 2.6 kernel so are very different.

I would strongly recommend backing up key files then doing a fresh install rather than trying to upgrade. This is because I've found:
1) Even with lots of planning you find things you didn't expect after the upgrade.
2) Even if everything works right on upgrade you tend to end up with a lot of files that are no longer relevant but you're never quite sure if it is OK to delete them. This clutters up you systems.

Also BEFORE you do this you might want to make sure you have your RHEL 2.1 disks so you can reinstall to revert if necessary. There are often challenges in putting the newer OS and kernel versions on older hardware. Usually there are solutions but it takes persistence to resolve them.

By the way RHEL5 is the latest - if you're upgrading why not do RHEL5 so you have more time before you need to go through this again.