[SOLVED] Repository has No Public Key

[mhumm2]

I suppose the obvious question is, how do I get the public key?

mark@AMD-64:~$ sudo apt update
Hit:1 http://us.archive.ubuntu.com/ubuntu bionic InRelease
Hit:2 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease                            
Get:3 http://security.ubuntu.com/ubuntu bionic-security InRelease [83.2 kB]                   
Get:4 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]                           
Get:5 http://ppa.launchpad.net/kubuntu-ppa/beta/ubuntu bionic InRelease [20.7 kB]                                                                 
Err:5 http://ppa.launchpad.net/kubuntu-ppa/beta/ubuntu bionic InRelease                         
 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 2836CB0A8AC93F7A
Reading package lists... Done
W: GPG error: http://ppa.launchpad.net/kubuntu-ppa/beta/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 2836CB0A8AC93F7A
E: The repository 'http://ppa.launchpad.net/kubuntu-ppa/beta/ubuntu bionic InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Yes, I did read man apt-secure. I understand signing and signature checking repositories from upload to user download, but I didn't see anything about "public" keys and I don't want to break anything.

[acheron]

The PPA you are trying to fetch from is disabled and has nothing in it. Remove it.

[mhumm2]

Okay, which one? I don't see any repository "ppa.launchpad.net/kubuntu-ppa/beta/ubuntu bionic"

# deb cdrom:[Kubuntu 18.04 LTS _Bionic Beaver_ - Release amd64 (20180426)]/ bionic main multiverse restricted universe

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

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ bionic-updates main restricted

## 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.
deb http://us.archive.ubuntu.com/ubuntu/ bionic universe
deb http://us.archive.ubuntu.com/ubuntu/ bionic-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.
deb http://us.archive.ubuntu.com/ubuntu/ bionic multiverse
deb http://us.archive.ubuntu.com/ubuntu/ bionic-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://us.archive.ubuntu.com/ubuntu/ bionic-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/ bionic partner

deb http://security.ubuntu.com/ubuntu/ bionic-security main restricted
deb http://security.ubuntu.com/ubuntu/ bionic-security universe
deb http://security.ubuntu.com/ubuntu/ bionic-security multiverse

[oshunluvr]

That's because you're looking only at the sources.list instead of what's in /etc/apt/sources.list.d. Try:

grep launchpad /etc/apt/sources.list.d/*

Then either delete the file containing the offending PPA or if there are other PPS's in the same file you want to keep, delete line(s) containing the offending PPA.

[kc1di]

you can do it in moun also by going to settings >cofigure software sources> Other software tab. just uncheck the offending ppa. Which is

http://ppa.launchpad.net/kubuntu-ppa/beta/ubuntu bionic InRelease

or you can remove it all together from there also.
good luck .
P.S. You must have added that ppa when you were upgrading from older version of Kubuntu to the 18.04 beta The ppa is no longer active since 18.04 is final.