Thanks for all the comments. Yes, Andrew, you are absolutely correct, I didn't read the output from aptitude carefully enough, partly because I didn't understand what much of it meant. So I'm especially grateful for your tutorial.
Up to now I hadn't thought that /root was full because as df -h shows below there is still some space left in / [EMAIL PROTECTED]:~$ df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/redcube-root 268M 215M 40M 85% / tmpfs 471M 0 471M 0% /lib/init/rw udev 10M 52K 10M 1% /dev tmpfs 471M 0 471M 0% /dev/shm /dev/hda1 236M 28M 197M 13% /boot /dev/mapper/redcube-home 136G 12G 118G 9% /home /dev/mapper/redcube-tmp 380M 11M 350M 3% /tmp /dev/mapper/redcube-usr 4.7G 3.4G 1.1G 76% /usr /dev/mapper/redcube-var 2.9G 293M 2.4G 11% /var [EMAIL PROTECTED]:~$ However, now I understand that the remaining room is not sufficient for aptitude to do its work. I think there are two possible solutions to this problem. One is to rm 2.6.18/4-amd64 from /lib/modules, shown below [EMAIL PROTECTED]:/lib/modules$ ls -a . .. 2.6.18-4-amd64 2.6.18-5-amd64 [EMAIL PROTECTED]:/lib/modules$ However, this may be a bad idea because it could cause another, new problem. Even if it doesn't break something it would be only a temporary solution: a future upgrade would probably run into the same problem. A better solution would be to move some space from /home to / , and perhaps to /usr. My HD has a big, non-encrypted partition for everything except /boot created by Logical Volume Management. This should make shifting space around fairly straight forward, although I don't yet know how to do it. I'll read the literature on this and if I'm confused I'll start another thread on LVM. Thanks again for all your help.