No Ubuntu 16.04, a guia de atualizações no centro de software mostra duas atualizações prontas para serem instaladas (OS e Thunderbird). Quando eu clico em instalar, a barra de progresso acende, mas depois apaga e nada acontece para que as duas atualizações permaneçam desinstaladas.
Eu corri sudo apt update e upgrade e obtive esta saída:
Ign:1 https://extras.ubuntu.com/ubuntu xenial InRelease
Err:2 https://extras.ubuntu.com/ubuntu xenial Release
404 Not Found [IP: 2001:67c:1360:8c01::23 80]
Hit:3 https://archive.canonical.com/ubuntu xenial InRelease
Hit:4 https://mirror.as29550.net/archive.ubuntu.com xenial InRelease
Hit:5 https://ppa.launchpad.net/alexlarsson/flatpak/ubuntu xenial InRelease
Hit:6 https://mirror.as29550.net/archive.ubuntu.com xenial-updates InRelease
Hit:7 https://repo.skype.com/deb stable InRelease
Hit:8 https://mirror.as29550.net/archive.ubuntu.com xenial-backports InRelease
Hit:9 https://mirror.as29550.net/archive.ubuntu.com xenial-security InRelease
Hit:11://ppa.launchpad.net/canonical-kernel-team/pti/ubuntu xenial InRelease
Get:10 https://ppa.launchpad.net/bit-team/stable/ubuntu xenial InRelease [17.5 kB]
Err:10 https://ppa.launchpad.net/bit-team/stable/ubuntu xenial InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4B6071B7D6FDC9D0
Reading package lists... Done
E: The repository 'http://extras.ubuntu.com/ubuntu xenial 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: GPG error: http://ppa.launchpad.net/bit-team/stable/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4B6071B7D6FDC9D0
E: The repository 'http://ppa.launchpad.net/bit-team/stable/ubuntu xenial 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.