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I have Kubuntu 18.04.01 installed on my PC. I'm a computer tech, but I have extremely limited knowledge of Linux. Everything is running fine, but I can no longer update the system.

sudo command doesn't work in the terminal and the Software Center fails to update. I am entering the correct password, but the system fails to update. The Software Center does successfully find the package to update. I get an error message from the Software Center, but it is a light grey background with dark grey text. I'm unable to read it before it shuts off.

Below is the text from the terminal after the root login fails. 

sudo apt-get update
[sudo] password for glen: 
Hit:1 repo.steampowered.com/steam precise InRelease
Hit:2 us.archive.ubuntu.com/ubuntu bionic InRelease                                                                
Get:3 security.ubuntu.com/ubuntu bionic-security InRelease [83.2 kB]                                               
Get:4 downloads.plex.tv/repo/deb public InRelease [3,408 B]                                                       
Ign:5 dl.google.com/linux/chrome/deb stable InRelease                                                              
Hit:6 us.archive.ubuntu.com/ubuntu bionic-updates InRelease                                         
Hit:7 us.archive.ubuntu.com/ubuntu bionic-backports InRelease                                      
Hit:8 dl.google.com/linux/chrome/deb stable Release                                                
Err:4 downloads.plex.tv/repo/deb public InRelease                           
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 97203C7B3ADCA79D
Reading package lists... Done
W: GPG error: downloads.plex.tv/repo/deb public InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 97203C7B3ADCA79D
E: The repository 'downloads.plex.tv/repo/deb public 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.
Zanna
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Glen Roberson
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    1: What exactly do you mean by "Below is the text from the terminal after the root login fails." If the login failed how could you access anything? 2: When posting terminal output, please include the actual command including the terminal prompts at the beginning and after the command has completed, whether successful or not. 3: Use this site's markdown formatting especially when posting code. – DK Bose Sep 20 '18 at 04:35
  • You most likely need to import the signing key from plex.tv. – Takkat Sep 20 '18 at 07:37
  • sudo is working fine - the error is from APT – Zanna Sep 20 '18 at 19:05

1 Answers1

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There is no problem with your password, all works. You have problem with the plex.tv repository.

Try removing that PPA, for example by unchecking it in Software Sources in Software and Updates. You can try adding it again if you need it.

Zanna
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marosg
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