apt-get upgrade not installing upgrades through crontab job

Question

After checking on how to make updates automatic with crontab, I've edited mine, as root, adding the following line:

00 11 * * * /usr/bin/apt-get upgrade -q -y >> /var/log/apt-upgrade.log

Now, if I manually run apt-get upgrade some minutes later, it'll show that it didn't install any of the upgrades. The log does not report any errors at all, nor warnings. It's just a common list

Reading package lists...
Building dependency tree...
Reading state information...
The following packages will be upgraded:
  binutils fontconfig fontconfig-config gnupg gpgv libcurl3
  libcurl4-openssl-dev libfontconfig1 libgcrypt11 libgcrypt11-dev libgd2-xpm
  libidn11 libidn11-dev libperl5.14 libpq5 libsqlite3-0 libssl-dev libssl-doc
  libssl1.0.0 libtiff4 linux-image-3.2.0-4-amd64 linux-libc-dev openjdk-7-jre
  openjdk-7-jre-headless openssh-client openssh-server openssl perl perl-base
  perl-modules ssh
31 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/93.7 MB of archives.
After this operation, 613 kB of additional disk space will be used.

Other things I've also tried (not all at the same time, obviously), with no results:

00 11 * * * apt-get upgrade -q -y >> /var/log/apt-upgrade.log
00 11 * * * root /usr/bin/apt-get upgrade -q -y >> /var/log/apt-upgrade.log
00 11 * * * apt-get upgrade -y >> /var/log/apt-upgrade.log

And nothing happens, no upgrades actually get installed. What am I doing wrong?

Answer 1

You need to set DEBIAN_FRONTEND=noninteractive. I seem to recall it was a bit tricky to find, since it's actually an option for debconf, not apt-get. However, it's mentioned e.g. here, and of course in the manual of debconf.

So, make a script that contains

#/bin/sh
DEBIAN_FRONTEND=noninteractive apt-get upgrade -q -y 

and run that from cron. And remember to run apt-get update too.

Of course perhaps you should be using unattended-upgrades or something that's especially designed for this.

But I have one Debian machine using this script, and it works ok:

#/bin/sh
apt-get -q -q  update 
if apt-get -s upgrade | grep -q "0 upgraded" ; then
        true
else
        DEBIAN_FRONTEND=noninteractive apt-get -y -q upgrade
fi

The first apt-get -s is there to suppress the output and useless email in case there's nothing to upgrade.

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