尝试下载存储库但出现此错误，在尝试下载任何其他存储库时也总是会发生这种情况。
W: The repository 'http://ppa.launchpad.net/osmoma/audio-recorder/ubuntu xenial Release' does not have a Release file.Reading package lists... Done
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://ppa.launchpad.net/osmoma/audio-recorder/ubuntu/dists/xenial/main/binary-amd64/Packages 503 Service Unavailable
E: Some index files failed to download. They have been ignored, or old ones used instead.