xubuntu@xubuntu:~$ sudo apt-get install firefox
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  ttf-lyx
The following packages will be upgraded:
  firefox
1 upgraded, 0 newly installed, 0 to remove and 208 not upgraded.
1 not fully installed or removed.
Need to get 0 B/25.5 MB of archives.
After this operation, 11.5 MB of additional disk space will be used.
(Reading database ... 134938 files and directories currently installed.)
Preparing to replace firefox 16.0.1+build1-0ubuntu1 (using .../firefox_21.0+build2-0ubuntu0.12.10.2_i386.deb) ...
Unpacking replacement firefox ...
dpkg: error processing /var/cache/apt/archives/firefox_21.0+build2-0ubuntu0.12.10.2_i386.deb (--unpack):
 unable to make backup link of `./usr/share/lintian/overrides/firefox' before installing new version: Input/output error
Please restart all running instances of firefox, or you will experience problems.
Processing triggers for desktop-file-utils ...
Errors were encountered while processing:
 /var/cache/apt/archives/firefox_21.0+build2-0ubuntu0.12.10.2_i386.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
xubuntu@xubuntu:~$