W: The repository 'http://extras.ubuntu.com/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.
E: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/xenial/main/source/Sources 404 Not Found [IP: 91.189.92.152 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.
我该如何解决它
答案1
快速检查表明 Xenial 不在那里，因此您尝试访问该位置的 Xenial 的任何内容都会失败：如您所见的目录结构这里在撰写此答案时，根本没有 Xenial 目录。
