how to upgrade from hardy to jaunty using terminal commands
 

i am presently using hardy but want to upgrade to jaunty.how can i do it using terminal commands?is there a risk of losing any other data in partitions other than home partition?please halp..

You can do this using aptitude.
1. change the repos in your /etc/apt/sources.list file replacing "hardy" with "jaunty".
2. From the command line run I'm not sure if this change involves a kernel change but if so you might have to do the manually. I'm not that familiar with the Buntu way of doing things so you'll need to check this.
cheers,
jdk

According to the Ubuntu Documentation, it cannot be done!

That's a generic (Ubuntu) warning not to skip levels - they do it every release.
Personally I haven't done an upgrade for years - it's such a shonky procedure with Ubuntu it just ain't worth the trouble.

Do a clean (re-)install - be careful with /home, and it works fine.

I've never had a problem with the Ubuntu upgrade procedure, and have upgraded several times now.

With different versions of Ubuntu, I have had problems with graphics tablets breaking, suspend to disk suspending to RAM instead, and virtual screen resolutions being bigger than the graphics chipset can support, but as far as I know these are all OS problems and not anything to do with the upgrade procedure.

The official recommended procedure to upgrade Ubuntu from the command-line is as follows. I believe you have to run this once for each version; you can't skip versions when upgrading Ubuntu (except to upgrade from one LTS release to another).

Source: http://www.ubuntu.com/getubuntu/upgrading

jdkaye's advice should also work, but do-release-upgrade has a better chance of migrating configuration files safely.

None of that has anything to do with the O/S - it is all the result of the packaging. Blame the Ubuntu devs.

Were you to do clean re-installs, you would most probably see significantly less of these sort of issues. As I alluded above.

Yup, clean install is always the safer thing to do, especially when you start skipping releases. If you are concerned about having to install all your software again, consider exporting the current package list from synaptic and importing it into your new system.