Here's what I'd try if I were doing such an upgrade.  Others can judge 
whether it needs modification, or whether a disk install from .iso files 
is likely to work with SL6:

In /boot put vmlinuz and initrd.img from X/Y/os/images/pxeboot/, where X 
is "ftp://ftp.scientificlinux.org/linux/scientific/6.0/" and Y is "i386" 
or "x86_64", depending on whether your computer is 32 or 64 bit.

In some partition which will be preserved during the upgrade, such as the 
one with home directories, make a directory called, say, "SL6Install". 
Copy to it the X/Y/iso/*Everything-DVD*.  Instead you may prefer the 
X/Y/iso/*Install-DVD.iso.  See the readme file in the X/Y/iso directory. 
Copying these .iso files to your preserved partition is only needed for a 
disk installation, and is not needed if you're going to do the 
installation over the internet.

Add to the end of /boot/grub/grub.conf lines

title SL6 Installation
         root (hd0,0)
         kernel /vmlinuz
         initrd /initrd.img

except "(hd0,0)" should be replaced by what you see for other grub 
entries, and I've assumed you have a boot partition.

Reboot your machine, selecting in grub "SL6 Installation", and do a disk 
installation from the SL6Install directory of the partition you decided to 
preserve.  You can alternatively install over the internet instead of from 
your own disk.


Steven Yellin

On Sat, 30 Apr 2011, Lucian Stroe wrote:

> Hello all,
>
> Maybe this subject was already discussed here, but I can't find the
> appropriate topic.
>
> Having a machine with SL5.5, how to get SL6.0 installed without burning
> another DVD's? On the SL website I found nothing about this...
>
> Thank you in advance,
>
> Lucian Stroe.
>