Freeing up some space on Ubuntu

I tried upgrading to Ubuntu Maverick Meerkat, but, as it often happens, the upgrade manager brushed me off saying I need to clear up about 970 MB of disk space on the root filesystem.
Time to buy a new hard drive, but in the meantime I still want to upgrade with what I have.

apt-get autoremove freed up some space, but more than an order of magnitude less than the gig I needed to find.

deborphan has always been a great tool to seek out the unneeded packages that use up disk space. If you run it without any arguments, it reports the libraries that are not required by any application. So you can safely remove every package deborphan reports unless you know you need it (for your own development, proprietary software you installed manually, etc.). When deborphan reports nothing, it's time to lax up the requirements:

deborphan -anz | sort -n

This lists all packages that are not required by other packages, even if they aren't libraries, and sorts them in a descending order by size. Old kernel images show up in this list near the bottom. There's usually more low-hanging fruit at the end of the list that can help you free up several hundred megs of space. Here you need to be careful not to delete something that you need from the system, as with these flags deborphan lists even packages that are apps rather than libraries, and even includes those that are suggested or recommended by other packages.

We're still several hundred megs short, but there are no obvious large packages to remove. The space is taken up by hundreds of relatively small ones. An effective technique I have found for this situation is start up Synaptic, order packages by origin, then go through restricted, multiverse and universe, sort packages by install status and size, and remove all the small packages you know nothing about, and various utilities you installed and used once. Sometimes it will threaten to remove a program that you need, then you need to back out. After you apply the changes, it's a good idea to close Synaptic and let apt-get autoremove and deborphan have a go again. If you're still not there, start up Synaptic again and prune Universe some more.

Presto! I got my gig (and more!) of free space by removing old kernels (480 MB), sacrificing Flightgear, QCad parts library, and lots of small utilities from Universe (900 MB).