Update failure

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 /
robin@redcube:~$ 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
robin@redcube:~$
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
robin@redcube:/lib/modules$ ls -a
. .. 2.6.18-4-amd64 2.6.18-5-amd64
robin@redcube:/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.