On my Debian 6.0.8 system the
/etc/cron.daily/apt file is missing. Therefore, unattended upgrades do not work.
How can I recreate/fix
first find which package contains the missing file:
$ dpkg --search /etc/cron.daily/apt apt: /etc/cron.daily/apt
which is that case is the package "apt", and then re-install it:
$ sudo apt-get -o Dpkg::Options::="--force-confmiss" --reinstall install apt
edit: added the option to force the miss conf
You should extract the apt deb package in a temp location and then copy the missing file to where it should be. For instance if your apt cache still contains the deb package apt you can do:
cd /tmp dpkg -x /var/cache/apt/archives/apt_0.9.7.9+deb7u1_amd64.deb . cp /tmp/etc/cron.daily/apt /etc/cron.daily/
If you don't have the deb file in your cache anymore, just download it and apply the same procedure.