If you don't have a RHN subscription then essentially you cannot upgrade your system over the network (at least not with the official RHEL packages) unless you have your own RPM repository.
Quote:
Originally Posted by
Hari_Ganesh
Please note that i don't have physical access to system. Hence CD/DVD option is ruled out.
Not quite. Most recent LOMs and hypervisors provide some sort of "media virtualization" that allows you to mout a remote CD-ROM as if you were physically in front of the server.
Having that in mind, there are several options to perform and upgrade. Downloading the DVD media is actually free if you have a RHN account (with or without a RHEL entitlement); Then you can use this media as your RPM repo and upgrade all your packages or use the "Upgrade" option after booting from the DVD.
Similar to the above method you can download the DVD in your own computer, transfer the packages over the network to the server in question and then install/upgrade all the packages. The only "drawback" of this method is that the system *may* still show as RHEL 5.4 system after the upgrade, even if all the 5.4 packages are already installed (although you might be able to trick some apps by just modifying /etc/redhat-release).