Can I choose to automatically download all updates and install the important ones?

Question

Why can't I select both of these?

Answer 1

I don't know exactly why the interface is limited and possibly counterintuitive like this. I'm ready to chalk it up to reducing complexity and adding sane defaults. For a desktop user, that often makes sense. However, if you are using a server, you wouldn't be using this method, and so I'll add some info on alternatives that provide more flexibility, at the expense of complexity. They also provide you (given a little time to familiarize yourself with them) a clearer view of exactly what actions will take place.

On the server side, the standard way to configure this is probably to use unattended-upgrades. This might be the best way to do this on the desktop as well.

Here's a decent guide on this (and some other Ubuntu methods): https://help.ubuntu.com/community/AutomaticSecurityUpdates

Note that this guide does not discourage using the Gnome Update Manager, which is GUI you are referring to. This is a user-editable wiki page, so I'm chalking this up to conflating server and desktop tools. (Though it is of course possible to install, e.g., Gnome on a server, too.)

Another method mentioned is cron. Cron has the advantage of being pretty transparent in what it does, and giving you great control, as it is typically hand-configured. This unfortunately also has the consequence of maintainability being limited to whatever system you create yourself.

An older but still available method is to use cron-apt. I've used this on Debian boxes, and it works on Ubuntu as well. I think the documentation is horrible, however.

cron-apt can optionally email status and updates. Here's an example:

CRON-APT RUN [/etc/cron-apt/config]: Wed Feb  9 04:00:01 CST 2011
CRON-APT SLEEP: 1315, Wed Feb  9 04:21:56 CST 2011
CRON-APT ACTION: 3-download
CRON-APT LINE: /usr/bin/apt-get dist-upgrade -d -y -o APT::Get::Show-Upgraded=true
Reading package lists...
Building dependency tree...
Reading state information...
The following packages will be upgraded:
  libfreetype6
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0B/385kB of archives.
After this operation, 0B of additional disk space will be used.
Download complete and in download only mode

A short but helpful page on cron-apt can be found on the TurnKey Linux Automatic Security Updates page. The descriptions work here because TurnKLey Linux is based on Ubuntu. Their cron-apt usage updates more aggressively, about which they have this to say:

In practice we've found it is very rare for an Ubuntu security update to break something, so we believe it is beneficial to configure software appliances to auto-update security fixes by default. Advanced users can always disable this mechanism and apply security fixes manually if they want.