Ubuntu – How to get security updates for restricted/partner packages

What I can think of:

• You might receive updates later than when using the main repository (due to the lag in synchronization),
• You might receive no updates at all if there's a problem with a mirror that's not closely monitored, and
• You might install problematic updates that have already been removed from the main repository (again, the lag in synchronization being the problem).

Security-wise I wouldn't worry that much, since packages and lists are all GPG-signed.

My question is just about detecting the availability of security updates

Yes, that's doable with the caveat that the normal apt-get update will do a full refresh when you next run it (20 MB means it's doing that anyway).

• sudo sh -c 'grep precise-security /etc/apt/sources.list > /etc/apt/secsrc.list

• And if you then run the following, you'll see if there are any security updates available (sample output):

  sudo sh -c 'apt-get -o Dir::Etc::sourcelist="secsrc.list" \
  -o Dir::Etc::sourceparts="-" update && \
  apt-get --assume-no upgrade'
  

• This tells apt-get to temporarily use the special security-only sources list, and then runs upgrade, automatically answering no.

• If there are any, run proper apt-get update (which will do a full refresh), and then upgrade.

• You could make the above a bash script with a simple grep/exit code check at the end if you don't feel like parsing the apt-get output :)