我一直在尝试弄清楚运行 apt-get update 时发生了什么。我尝试过查看源文件，也尝试过使用 Ubuntu Tweak 清理源列表，但都不起作用。
当我运行 apt-get update 时，我得到了这个：
Reading package lists... Done
N: Skipping acquire of configured file 'main/binary-i386/Packages' as repository 'https://packages.microsoft.com/repos/vscode stable InRelease' doesn't support architecture 'i386'
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04 Release: The following signatures were invalid: KEYEXPIRED 1496576244
W: The repository 'http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial Release' does not have a Release file.
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.
W: Failed to fetch http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04/Release.gpg The following signatures were invalid: KEYEXPIRED 1496576244
E: Failed to fetch http://ppa.launchpad.net/tualatrix/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.
W: Duplicate sources.list entry http://packages.microsoft.com/repos/vscode stable Release
答案1
您正在尝试安装（或更新）该Ubuntu TweakPPA 所调用的软件包tualatrix/ppa，该软件包在此页面有描述：https://launchpad.net/~tualatrix/+archive/ubuntu/ppa。但是，此 PPA 不包含任何与您的 Ubuntu 版本 ( xenial) 兼容的软件包，因为它在 之后停止了支持trusty。
您可以尝试下载deb文件trusty并安装它，但有可能无法满足依赖关系。
本文更详细地解释发生了什么，并建议您安装Unity tweak。
要清除此问题，请tualatrix从sources.list文件中删除包含 的行和/或删除任何包含 的文件tualatrix。sources.list.d或者，安装ppa-purge并执行sudo ppa-purge tualatrix/ppa。
最后，sudo apt update && sudo apt upgrade再次运行。