Add ability for mirrors to distinguish interactive and non-interactive apt runs

Obviously this may be equally relevant to unattended-upgrades.

/usr/lib/apt/apt.systemd.daily should force set a Useragent apt.systemd.daily, for all operations.

irrespective how/who/what invoked /usr/lib/apt/apt.systemd.daily

So, I think we want to do that for apt-daily.service which does the downloading of package lists and updates; but not for the actual upgrade job - which might fetch any remaining packages.

https://salsa.debian.org/apt-team/apt/-/merge_requests/114

The attached merge proposal adds the name of the systemd unit that we are running under to the HTTP User-Agent field. Is that sufficient?

Probably ! What is it going to be for interactive uses though ?

Well, nothing, absence of service is interactive?

Note that there were some I think somewhat valid privacy concerns to exposing the service name.

Maybe it's enough to know if apt ran as part of a systemd service, but not which service, or we build a whitelist of services (or check if they are inside /lib/systemd/system - so we do not send local service names). Currently we do have a blacklist that matches user@ services.

Another approach was to send whether a tty is attached, but I believe that's a bit less useful

I think "User-Agent: Debian APT-HTTP/1.3 (2.0.1) non-interactive" would be enough.

This bug was fixed in the package apt - 2.0.2

---------------
apt (2.0.2) unstable; urgency=medium

  [ Boyuan Yang ]
  * Simplified Chinese program translation update (Closes: #955023)

  [ Frans Spiesschaert ]
  * Dutch program translation update (Closes: #955505)

  [ Marco Ippolito ]
  * Fix gramma in apt(8): "by append(+ing) a" (Closes: #955412)

  [ Chris Leick ]
  * German manpage translation update
  * Fix "string match{ing,es}" and whitespace typo in apt-patterns(7)

  [ Julian Andres Klode ]
  * test/integration/apt.pem: Regenerate with SHA2 hashes to make the
    test work with stricter gnutls in Ubuntu which rejects SHA1
  * ubuntu: http: Add non-interactive to user agent if run by systemd
    (LP: #1825000)

 -- Julian Andres Klode <email address hidden> Thu, 09 Apr 2020 12:21:07 +0200

eoan has reached end of life, so this bug will not be fixed for that release