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I have about 7 Debian servers I manage, and I would like to set them to automatically update themselves. So, I created a script as such:

apt-get update
apt-get upgrade

and placed it on the root's crontab list. Unfortunately, it always hangs on the Upgrade section, asking if I'm sure I want to upgrade. Because it's a cron job, I don't see the output until it emails me saying it's failed. Is there a way to have it skip that prompt, and just do the upgrade automatically?

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... or cron-apt. – derobert Dec 30 '13 at 20:02
up vote 24 down vote accepted

Use the -y option to apt-get to have it not ask. From man apt-get:

   -y, --yes, --assume-yes
       Automatic yes to prompts; assume "yes" as answer to all prompts and
       run non-interactively. If an undesirable situation, such as
       changing a held package, trying to install a unauthenticated
       package or removing an essential package occurs then apt-get will
       abort. Configuration Item: APT::Get::Assume-Yes.

You can also set the DEBIAN_FRONTEND env variable

DEBIAN_FRONTEND=noninteractive apt-get -y upgrade
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What does DEBIAN_FRONTEND do? Is it used for other processes as well? – Canadian Luke Dec 30 '13 at 19:58
I'm trying this on my home server, and will choose the best answer as soon as it runs – Canadian Luke Dec 30 '13 at 20:04
@CanadianLuke see here for DEBIAN_FRONTEND. It's not mentioned in my Debian's man debconf though, so it may be an Ubuntu thing. – terdon Dec 30 '13 at 20:31
@terdon you don't have the -doc package for debconf. It's in the 7 section of the man man 7 debconf ;) – Braiam Dec 30 '13 at 20:48
@Braiam ah, OK, I saw that and tried man 7 debconf but got nothing. Now I know why :) – terdon Dec 30 '13 at 20:51

Well, maybe you are using the wrong tool. unattended-upgrades package installs security upgrades in daily basis (can be configured), you can configure what packages to upgrade or not upgrade, etc. Can be installed using:

sudo apt-get install unattended-upgrades

From man unattended-upgrades:

The configuration is done via the apt configuration mechanism. The default configuration file can be found at /etc/apt/apt.conf.d/50unattended-upgrades

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@CanadianLuke it reads all the configurations in /etc/apt/apt.conf.d/ but only those starting with Unattended-Upgrade:: get parsed. – Braiam Dec 30 '13 at 20:04
I am trying this on one of the servers at work, and will choose the best answer as soon as it runs – Canadian Luke Dec 30 '13 at 20:05

A generic tool for this kind of thing is yes:

       Repeatedly output a line with all specified STRING(s), or 'y'.

So, for example, you could do

yes | sudo apt-get upgrade 

Please note that in the specific case of apt-get upgrade using the options suggested by @Braiam or @ArthurUlfeldt is better.

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The line I paste when I want to do it manually is apt-get update && yes | apt-get upgrade (our servers aren't supposed to use sudo... Don't ask...) – Canadian Luke Aug 14 '14 at 18:54

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