[linux] problemen met rpositories

[paai]

Hallo,

in een vlaag van verstandverbijstering ben ik eens gaan proberen 
LineageOS kernels voor een Android phone the bakken, maar voor ik 
daaraan toekom heb ik al problemen met Linux. Of liever, met java (wat 
anders).

Mijn (K)ubuntu systeem is Disco Dingo (19.04).

Bij het installeren wordt het volgende

     $ sudo add-apt-repository ppa:openjdk-r/ppa

Dit verslikt zich als volgt (zie onder). Ik heb in /etc/apt/sources.list 
vervolgens old-releases vervangen door us.archives, maar dat gaf nog 
meer errors.

dan maar mythbuntu  toegevoegd:

     $ sudo add-apt-repository ppa:mythbuntu/0.28

leverde precies hetzelfde op.

Iemand suggesties?


------------

Ign:1 http://ppa.launchpad.net/mythbuntu/0.28/ubuntu disco InRelease
Hit:2 http://dl.google.com/linux/chrome/deb stable InRelease 

Hit:3 http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu disco 
InRelease
Hit:4 http://old-releases.ubuntu.com/ubuntu disco InRelease 

Hit:5 http://old-releases.ubuntu.com/ubuntu disco-updates InRelease 

Get:6 https://repo.skype.com/deb stable InRelease [4501 B] 

Hit:7 http://ppa.launchpad.net/openjdk-r/ppa/ubuntu disco InRelease 

Hit:8 http://old-releases.ubuntu.com/ubuntu disco-backports InRelease
Hit:9 http://old-releases.ubuntu.com/ubuntu disco-security InRelease 

Hit:10 http://ppa.launchpad.net/stebbins/handbrake-releases/ubuntu disco 
InRelease
Hit:11 http://ppa.launchpad.net/ubuntu-x-swat/updates/ubuntu disco InRelease
Err:12 http://ppa.launchpad.net/mythbuntu/0.28/ubuntu disco Release
   404  Not Found [IP: 91.189.95.85 80]
Ign:13 https://repo.windscribe.com/kubuntu zesty InRelease
Err:14 https://repo.windscribe.com/kubuntu zesty Release
   404  Not Found [IP: 104.20.26.217 443]
Err:6 https://repo.skype.com/deb stable InRelease
   The following signatures were invalid: EXPKEYSIG 1F3045A5DF7587C3 
Skype Linux Client Repository <se-um op microsoft.com>
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/mythbuntu/0.28/ubuntu disco 
Release' does not have a Release file.
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.
E: The repository 'https://repo.windscribe.com/kubuntu zesty Release' 
does not have a Release file.
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.
W: An error occurred during the signature verification. The repository 
is not updated and the previous index files will be used. GPG error: 
https://repo.skype.com/deb stable InRelease: The following signatures 
were invalid: EXPKEYSIG 1F3045A5DF7587C3 Skype Linux Client Repository 
<se-um op microsoft.com>