Need help to troubleshoot automatic updates (stopped downloading packages in one system).

[Sergio <secipolla@gmail.com>]

Hello,
I have two Debian sid installations in this machine and I have set up
both to update the package list and download upgradable packages
automatically.
Initially this worked fine but after some time, in one of the systems
it only runs 'apt-get update' and 'apt-get autoclean' and finishes the
cron.daily job without running 'debdelta-upgrade' or 'apt-get -d
dist-upgrade'.

I have noticed before that some things affected its behaviour. For
instance, IIRC, if I ran 'aptitude update' manually, then the next day
the apt cron.daily job wouldn't run as if it had already run.
Another thing, this one anacron's 'fault' probably, is that if I
shutdown/reboot before the cron job had finished then it wouldn't run
again that day as the timestamp is updated right when the job starts.
I'm only mentioning these things because I suspect something is
stopping it from downloading the packages.
* I just noticed /var/lib/apt/periodic:

total 0
-rw-r--r-- 1 root root 0 Feb 27 07:57 autoclean-stamp
-rw-r--r-- 1 root root 0 Feb 14 08:37 download-upgradeable-stamp
-rw-r--r-- 1 root root 0 Feb 14 08:36 update-stamp

so I'll clear this directory and see if tomorrow it works.

Just to complete the picture, I tried many things to track down what
could be broken. I changed unrelated apt configuration (in both
installations just to make sure and the one that works, works and this
one doesn't no matter what), I disabled/re-enabled debdelta (I remember
one day it wasn't working) and the package downloading itself and
sometimes I would just don't touch apt for a day or even not boot this
system where it's not downloading the packages so I've been trying to
fix this for at least 10 days.

Both installations have the same configuration
in /etc/apt/apt.conf.d/02periodic

APT::Periodic::Enable "1";
#  - Enable the update/upgrade script (0=disable)

APT::Periodic::Update-Package-Lists "1";
#  - Do "apt-get update" automatically every n-days (0=disable)

APT::Periodic::Download-Upgradeable-Packages "1";
#  - Do "apt-get upgrade --download-only" every n-days (0=disable)

APT::Periodic::Download-Upgradeable-Packages-Debdelta "1";
#  - Use debdelta-upgrade to download updates if available (0=disable)

APT::Periodic::AutocleanInterval "1";
#  - Do "apt-get autoclean" every n-days (0=disable)

And in apt.conf all I have is settings for install-recommends (and
currently in this system I've even commented all out there just so it
doesn't affect in any way).

So I'll see if clearing /var/lib/apt/periodic makes it start working
fine again tomorrow but if anyone has some other tip, I'm grateful.