I'd like to downgrade GNOME because 3.20 on my Ubuntu 16.04 is a mess. There are countless sources on the Internet (including askubuntu) saying how to do this, and it's always:
sudo ppa-purge ppa:gnome3-team/gnome3-staging
sudo ppa-purge ppa:gnome3-team/gnome3
(optionally also sudo ppa-purge ppa:gnome3-team/gnome3-next)
However, I'm getting nowhere with this.
$ sudo ppa-purge ppa:gnome3-team/gnome3-staging:
Updating packages lists
W: GPG error: http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04 Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A7D1D38BEB6D886
W: The repository 'http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04 Release' is not signed.
W: The repository 'http://ppa.launchpad.net/cardapio-team/cardapio-ppa/ubuntu xenial Release' does not have a Release file.
W: The repository 'http://ppa.launchpad.net/cardapio-team/unstable/ubuntu xenial Release' does not have a Release file.
W: The repository 'http://ppa.launchpad.net/synapse-core/ppa/ubuntu xenial Release' does not have a Release file.
E: Failed to fetch http://ppa.launchpad.net/cardapio-team/cardapio-ppa/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Failed to fetch http://ppa.launchpad.net/cardapio-team/unstable/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Failed to fetch http://ppa.launchpad.net/synapse-core/ppa/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
Warning: apt-get update failed for some reason
$ sudo ppa-purge ppa:gnome3-team/gnome3:
Updating packages lists
W: The repository 'http://ppa.launchpad.net/cardapio-team/cardapio-ppa/ubuntu xenial Release' does not have a Release file.
W: The repository 'http://ppa.launchpad.net/cardapio-team/unstable/ubuntu xenial Release' does not have a Release file.
W: The repository 'http://ppa.launchpad.net/synapse-core/ppa/ubuntu xenial Release' does not have a Release file.
W: GPG error: http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04 Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A7D1D38BEB6D886
W: The repository 'http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04 Release' is not signed.
E: Failed to fetch http://ppa.launchpad.net/cardapio-team/cardapio-ppa/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Failed to fetch http://ppa.launchpad.net/cardapio-team/unstable/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Failed to fetch http://ppa.launchpad.net/synapse-core/ppa/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
Warning: apt-get update failed for some reason
GNOME stays the same version after reboot. Excuse me if this is just a matter of googling some part of the output, I have tried to search also for something general concerning ppa-purge failing. I'm a below-average end user. I'll be happy to provide more info.
As requested, $ sudo apt-get update output, and $ sudo apt-get upgrade output:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
