Eu tenho um problema ao executar sudo apt-get update :
W:The repository 'http://old-releases.ubuntu.com/ubuntu xenial-security Release' does not have a Release file.,
W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use.,
W:See apt-secure(8) manpage for repository creation and user configuration details.,
W:The repository 'http://ppa.launchpad.net/ubuntu-audio-dev/ppa/ubuntu xenial Release' does not have a Release file.,
W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use.,
W:See apt-secure(8) manpage for repository creation and user configuration details.,
W:Failed to fetch http://de.old-releases.ubuntu.com/ubuntu/dists/xenial/InRelease Could not resolve 'de.old-releases.ubuntu.com',
W:Failed to fetch http://de.old-releases.ubuntu.com/ubuntu/dists/xenial-updates/InRelease Could not resolve 'de.old-releases.ubuntu.com',
W:Failed to fetch http://de.old-releases.ubuntu.com/ubuntu/dists/xenial-backports/InRelease Could not resolve 'de.old-releases.ubuntu.com',
E:Failed to fetch http://old-releases.ubuntu.com/ubuntu/dists/xenial-security/main/binary-amd64/Packages 404 Not Found,
E:Failed to fetch http://ppa.launchpad.net/ubuntu-audio-dev/ppa/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found,
W:Some index files failed to download. They have been ignored, or old ones used instead.
devo adicionar algum repositório diferente?