I bet the problem has something to do with the residue left with the _apt owner stuff...
# find /var/lib/apt/lists/partial -ls 49345 17 drwx------ 2 _apt root 16384 Sep 25 18:52 /var/lib/apt/lists/partial 49381 18 -rw-r--r-- 1 root root 18409 Aug 15 09:21 /var/lib/apt/lists/partial/ftp.tw.debian.org_debian_dists_experimental_contrib_i18n_Translation-en OK I moved that file to /tmp and now indeed "aptitude update" is working. I moved it back, and "aptitude update" is still working (but maybe that is because it was freshly updated.) As this is on a "sneakernet" disk, I use chown root:root lists chown _apt:root lists/partial at boot. OK I'll use chown -R _apt:root lists/partial or better yet find lists/partial -type f -delete
