No package manager installed

[acheron]

Well, you have done something there which has disabled more sources (commented out with a #) than you should have.

In particular the 'deb' lines with contain 'universe'.

Kubuntu packages exist in the 'universe' pocket, so having that disabled will mean apt or any other package management tool with simply not know they exist to find them.

You may be able to use software-properties-kde to toggle and restore the lines, but if not then you may be best replacing the sources.list content with something like the default.

e.g.

Note the bolded lines, with are the enabled ones.

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
[B]deb http://archive.ubuntu.com/ubuntu xenial main restricted[/B]

## Major bug fix updates produced after the final release of the
## distribution.
[B]deb http://archive.ubuntu.com/ubuntu xenial-updates main restricted[/B]

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
[B]deb http://archive.ubuntu.com/ubuntu xenial universe[/B]
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial universe
[B]deb http://archive.ubuntu.com/ubuntu xenial-updates universe[/B]
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
[B]deb http://archive.ubuntu.com/ubuntu xenial multiverse[/B]
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial multiverse
[B]deb http://archive.ubuntu.com/ubuntu xenial-updates multiverse[/B]
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu xenial-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu xenial partner
# deb-src http://archive.canonical.com/ubuntu xenial partner

[B]deb http://archive.ubuntu.com/ubuntu xenial-security main restricted
deb http://archive.ubuntu.com/ubuntu xenial-security universe[/B]
# deb-src http://security.ubuntu.com/ubuntu xenial-security universe
[B]deb http://archive.ubuntu.com/ubuntu xenial-security multiverse[/B]
# deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse

[Guest]

Thank you, that helped!

[acheron]

Thank you, that helped!

Great.