Here is a tip I ended using on a machine that didn’t have a CD drive and no connection to the internet. It already had Ubuntu installed and needed to upgrade to the next release. First you need to download the Ubuntu Alternate CD image (text base install) ubuntu-1.10-alternate-i386.iso
1. Mount the downloaded ISO image in the CD drive mounting point by typing the following:
sudo mount -t iso9660 ubuntu-9.10-alternate-i386.iso /cdrom -o loop
2. Run the upgrading application found on the CD.
gksu “sh /cdrom/cdromupgrade”
3. The machine will now upgrade and eventually reboot. You may now remove the CD entry to the image found in the file: /etc/apt/sources.list
You might want to keep the image for software sources and mount it anytime you wish to install new software.