No longer able to start Discover from Application Launcher

[boxcorner]

Thanks again for your help.
When I used ppa-purge

ron@rdh-NUC8i3BEH:~$ sudo ppa-purge http://ppa.launchpad.net/michael-gruz/canon-trunk
[sudo] password for ron: 
Updating packages lists
E: The repository 'http://ppa.launchpad.net/michael-gruz/canon-trunk/ubuntu focal Release' does not have a Release file.
W: GPG error: http://cz.archive.ubuntu.com/ubuntu precise Release: The  following signatures couldn't be verified because the public key is not  available: NO_PUBKEY 40976EAF437D05B5
Warning:  apt-get update failed for some reason

So I deleted two these files

ron@rdh-NUC8i3BEH:/etc/apt/sources.list.d$ sudo rm /etc/apt/sources.list.d/michael-gruz-ubuntu-canon-trunk-focal.list
ron@rdh-NUC8i3BEH:/etc/apt/sources.list.d$ sudo rm /etc/apt/sources.list.d/michael-gruz-ubuntu-canon-trunk-focal.list.save

Now when I run apt update

ron@rdh-NUC8i3BEH:/etc/apt/sources.list.d$ sudo apt update
[sudo] password for ron: 
Hit:1 http://fr.archive.ubuntu.com/ubuntu focal InRelease
Hit:2 http://ppa.launchpad.net/linuxuprising/libpng12/ubuntu focal InRelease                     
Ign:3 http://cz.archive.ubuntu.com/ubuntu precise InRelease                                      
Hit:4 http://fr.archive.ubuntu.com/ubuntu focal-updates InRelease                                
Hit:5 http://cz.archive.ubuntu.com/ubuntu precise Release                  
Hit:6 http://fr.archive.ubuntu.com/ubuntu focal-backports InRelease        
Get:7 http://cz.archive.ubuntu.com/ubuntu precise Release.gpg [198 B]
Hit:8 http://security.ubuntu.com/ubuntu focal-security InRelease
Ign:7 http://cz.archive.ubuntu.com/ubuntu precise Release.gpg
Fetched 198 B in 1s (302 B/s)
Reading package lists... Done
Building dependency tree       
Reading state information... Done
71 packages can be upgraded. Run 'apt list --upgradable' to see them.
W: GPG error: http://cz.archive.ubuntu.com/ubuntu precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5

I thought I followed your instructions.
What am I doing wrong?
How do I get rid of precise?

[Don B. Cilly]

Well,
sudo ppa-purge http://ppa.launchpad.net/michael-gruz/canon-trunk
seems to have got rid of that one.
So maybe
sudo ppa-purge http://cz.archive.ubuntu.com/ubuntu precise
will get rid of the other one?

[claydoh]

Well,
sudo ppa-purge http://ppa.launchpad.net/michael-gruz/canon-trunk
seems to have got rid of that one.
So maybe
sudo ppa-purge http://cz.archive.ubuntu.com/ubuntu precise
will get rid of the other one?

Maybe, maybe not. Depends on how it was added in the first place.
May require editing the /etc/apt/sources/list

[mr_raider]

Run the following command and paste the results. Here is mine:

[FONT=monospace][COLOR=#54FF54][B]mr_raider@EliteBook-725-G3[/B][/COLOR]:[COLOR=#5454FF][B]/etc/apt[/B][/COLOR]$ cat /etc/apt/sources.list
# deb cdrom:[neon user _Bionic_ - Build amd64 LIVE Binary 20181011-05:55]/ bionic main multiverse restricted universe

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

## Major bug fix updates produced after the final release of the
## distribution.
deb http://ca.archive.ubuntu.com/ubuntu/ bionic-updates main restricted
# deb-src http://ca.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://ca.archive.ubuntu.com/ubuntu/ bionic universe
# deb-src http://ca.archive.ubuntu.com/ubuntu/ bionic universe
deb http://ca.archive.ubuntu.com/ubuntu/ bionic-updates universe
# deb-src http://ca.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://ca.archive.ubuntu.com/ubuntu/ bionic multiverse
# deb-src http://ca.archive.ubuntu.com/ubuntu/ bionic multiverse
deb http://ca.archive.ubuntu.com/ubuntu/ bionic-updates multiverse
# deb-src http://ca.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://ca.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
# deb-src http://ca.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-src http://archive.canonical.com/ubuntu/ bionic partner

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

[/FONT]

[boxcorner]

ron@rdh-NUC8i3BEH:/etc/apt$ cat /etc/apt/sources.list
# deb cdrom:[Kubuntu 20.04 LTS _Focal Fossa_ - Release amd64 (20200423)]/ focal main multiverse restricted universe

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

## Major bug fix updates produced after the final release of the
## distribution.
deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates main restricted
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-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://fr.archive.ubuntu.com/ubuntu/ focal universe
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal universe
deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates universe
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-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://fr.archive.ubuntu.com/ubuntu/ focal multiverse
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal multiverse
deb http://fr.archive.ubuntu.com/ubuntu/ focal-updates multiverse
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-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://fr.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-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 focal partner
# deb-src http://archive.canonical.com/ubuntu focal partner

deb http://security.ubuntu.com/ubuntu focal-security main restricted
# deb-src http://security.ubuntu.com/ubuntu focal-security main restricted
deb http://security.ubuntu.com/ubuntu focal-security universe
# deb-src http://security.ubuntu.com/ubuntu focal-security universe
deb http://security.ubuntu.com/ubuntu focal-security multiverse
# deb-src http://security.ubuntu.com/ubuntu focal-security multiverse

# This system was installed using small removable media
# (e.g. netinst, live or single CD). The matching "deb cdrom"
# entries were disabled at the end of the installation process.
# For information about how to configure apt package sources,
# see the sources.list(5) manual.

[mr_raider]

That looks good. Go throught the folder

/etc/apt/sources.list.d

Check every .list file. Open each one and make sure they do NOT have the word "precise" in any of them. It should be "focal".

Next open a terminal and type

sudo software-properties-kde

On the first tab set the download server to the main server. This will insure your France mirror is not borked.

[Don B. Cilly]

Open each one and make sure they do NOT have the word "precise" in any of them

Or...
grep precise *
in that folder will find any occurrences pretty quickly...

(Hint: F4 - in Dolphin - will open a mini-terminal in that folder).

[boxcorner]

Thank you mr_raider. I found one file containing "precise":

ron@rdh-NUC8i3BEH:/etc/apt/sources.list.d$ grep precise *
extra.list:deb [trusted=yes] [URL]http://cz.archive.ubuntu.com/ubuntu[/URL] [B][COLOR=#ff0000]precise[/COLOR][/B] main universe

So, I changed "precise" to "focal".
Then using Guake opened terminal and typed, sudo software-properties-kde, which opened a GUI window.
When I set the download server to main server an error message was displayed. Please see attachment.
The second attachment shows the Software Sources pop-up window, after I acknowledged the error.
What is the significance of <2> after the title?
So, with main server selected I checked the sources.list again:

ron@rdh-NUC8i3BEH:/etc/apt$ cat /etc/apt/sources.list
# deb cdrom:[Kubuntu 20.04 LTS _Focal Fossa_ - Release amd64 (20200423)]/ focal main multiverse restricted universe

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

## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu focal-updates main restricted
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-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://archive.ubuntu.com/ubuntu focal universe
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal universe
deb http://archive.ubuntu.com/ubuntu focal-updates universe
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-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://archive.ubuntu.com/ubuntu focal multiverse
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal multiverse
deb http://archive.ubuntu.com/ubuntu focal-updates multiverse
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-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 focal-backports main restricted universe multiverse
# deb-src http://fr.archive.ubuntu.com/ubuntu/ focal-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 focal partner
# deb-src http://archive.canonical.com/ubuntu focal partner

deb http://archive.ubuntu.com/ubuntu focal-security main restricted
# deb-src http://security.ubuntu.com/ubuntu focal-security main restricted
deb http://archive.ubuntu.com/ubuntu focal-security universe
# deb-src http://security.ubuntu.com/ubuntu focal-security universe
deb http://archive.ubuntu.com/ubuntu focal-security multiverse
# deb-src http://security.ubuntu.com/ubuntu focal-security multiverse

# This system was installed using small removable media
# (e.g. netinst, live or single CD). The matching "deb cdrom"
# entries were disabled at the end of the installation process.
# For information about how to configure apt package sources,
# see the sources.list(5) manual.

Then I ran apt update:

ron@rdh-NUC8i3BEH:/etc/apt$ sudo apt update
E: Conflicting values set for option Trusted regarding source http://archive.ubuntu.com/ubuntu/ focal
E: The list of sources could not be read.

What have I done wrong now?

[boxcorner]

Don, thank you for the tips. Noted.

[Don B. Cilly]

Hmm. Probably a totally useless reply, but.
Having got curious, I just removed the comments from your sources.list (with sed) and from mine.

They look exactly the same, except I have
deb http://es.archive.ubuntu.com/ubuntu/ bionic universe
and you have
deb http://archive.ubuntu.com/ubuntu/ focal universe
and so on for every repo. I have .es., you don't.

I see you have your software-properties set to download from "Main server".
Maybe try setting it to use one of the mirrors - maybe the one for France?
I know... unlikely. But having done the comparison work... ;·)

[mr_raider]

GEt rid of the file extra.list in sources.list.d

[boxcorner]

Thank you Don.
Well, mr_raider suggested that I change to using "Main server" ...
So, I ran sudo software-properties-kde and selected Download from "Server for France"

~$ sudo software-properties-kde
QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'

Software Sources now shows Download from "Custom servers".

sudo apt update
Hit:1 http://fr.archive.ubuntu.com/ubuntu focal InRelease                                                                                                     
Hit:2 http://archive.ubuntu.com/ubuntu focal InRelease                                                                                                        
Hit:3 http://ppa.launchpad.net/linuxuprising/libpng12/ubuntu focal InRelease                                                                                  
Hit:4 http://fr.archive.ubuntu.com/ubuntu focal-updates InRelease                                                                                             
Hit:5 http://fr.archive.ubuntu.com/ubuntu focal-backports InRelease
Hit:6 http://fr.archive.ubuntu.com/ubuntu focal-security InRelease
Reading package lists... Done
Building dependency tree       
Reading state information... Done
59 packages can be upgraded. Run 'apt list --upgradable' to see them.

That looks much better, doesn't it?
All Hits mention focal, but 59 packages can be upgraded? How?
Having lost the use of Discover, I'm all at sea.
I see Muon has a Check for Upgrades button, but I don't see how to upgrade them if apt update doesn't do it.
And that message: QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
Is it something that I should change?
After rebooting, I ran apt update again and this is what I got:

$ sudo apt update
[sudo] password for ron: 
Hit:1 http://fr.archive.ubuntu.com/ubuntu focal InRelease           
Hit:2 http://archive.ubuntu.com/ubuntu focal InRelease              
Hit:3 http://ppa.launchpad.net/linuxuprising/libpng12/ubuntu focal InRelease
Get:4 http://fr.archive.ubuntu.com/ubuntu focal-updates InRelease [107 kB]
Get:4 http://fr.archive.ubuntu.com/ubuntu focal-updates InRelease [107 kB]                                                                                                                                        
Get:5 http://fr.archive.ubuntu.com/ubuntu focal-backports InRelease [98,3 kB]
Get:6 http://fr.archive.ubuntu.com/ubuntu focal-security InRelease [107 kB]
Get:7 http://fr.archive.ubuntu.com/ubuntu focal-updates/main i386 Packages [122 kB]
Get:8 http://fr.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages [236 kB]
Get:9 http://fr.archive.ubuntu.com/ubuntu focal-updates/main amd64 DEP-11 Metadata [149 kB]
Get:10 http://fr.archive.ubuntu.com/ubuntu focal-updates/universe amd64 Packages [125 kB]
Get:11 http://fr.archive.ubuntu.com/ubuntu focal-updates/universe i386 Packages [66,4 kB]                                                                                                                         
Get:12 http://fr.archive.ubuntu.com/ubuntu focal-updates/universe amd64 DEP-11 Metadata [167 kB]                                                                                                                  
Get:13 http://fr.archive.ubuntu.com/ubuntu focal-backports/universe amd64 DEP-11 Metadata [532 B]                                                                                                                 
Get:14 http://fr.archive.ubuntu.com/ubuntu focal-security/main i386 Packages [44,1 kB]                                                                                                                            
Get:15 http://fr.archive.ubuntu.com/ubuntu focal-security/main amd64 Packages [127 kB]                                                                                                                            
Get:16 http://fr.archive.ubuntu.com/ubuntu focal-security/main Translation-en [46,2 kB]                                                                                                                           
Get:17 http://fr.archive.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [21,2 kB]                                                                                                                    
Get:18 http://fr.archive.ubuntu.com/ubuntu focal-security/restricted amd64 Packages [25,3 kB]                                                                                                                     
Get:19 http://fr.archive.ubuntu.com/ubuntu focal-security/restricted Translation-en [6 812 B]                                                                                                                     
Get:20 http://fr.archive.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [35,8 kB]                                                                                                                
Fetched 1 404 kB in 40s (35,1 kB/s)                                                                                                                                                                               
Reading package lists... Done
Building dependency tree       
Reading state information... Done
59 packages can be upgraded. Run 'apt list --upgradable' to see them.

I don't understand why it's a longer, different list, nor why there are two Get:4.

[Don B. Cilly]

sudo apt full-upgrade
will let you update.
In Muon, you have a "Full Upgrade" option, which does...the same :·)

You might want to check out this little script, jokingly called Micro-Muon.
It does a lot of what Muon does (well most of the important parts) using CLI output, quite informative.

[EDIT] Before I wrote the micro-muon, I used this method (with an alias) to update my system..

[boxcorner]

Ah, thank you ...
So, I ran sudo apt full-upgrade and all seemed to be okay, likewise sudo apt update.
I see "Full Upgrade" in Muon, but it is greyed out. Presumably it is only enabled when it can be used.
I will have a look at Micro-Muon and the alternative using aliases.
Thanks again for all your help and for the tips.
There remains just one other little thing which puzzles me. It's a message which flashes up briefly during the boot sequence.
If I manage to grab it somehow then I might ask for help, if I can't fix it myself.
It has appeared since I installed 20.04 which ran perfectly smoothly until I messed it up by trying to install the printer/scanner drivers.

[Don B. Cilly]

I see "Full Upgrade" in Muon, but it is greyed out. Presumably it is only enabled when it can be used.

Correct. It's greyed out if there are no updates to be installed.

To grab the boot message, I guess, take a little video with your phone, get a screencap of it.