因为使用apt-get install安装mysql找不到package，所以按照搜索解决方案为apt-get update。但是尝试了几乎所有的方法，都是失败的。不知道他们是怎么安装成功的。报错提示：

Reading package lists... Done
W: The repository 'https://mirrors.tuna.tsinghua.edu.cn/ubuntu yakkety 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: The repository 'https://mirrors.tuna.tsinghua.edu.cn/ubuntu yakkety-updates 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: The repository 'https://mirrors.tuna.tsinghua.edu.cn/ubuntu yakkety-backports 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: The repository 'https://mirrors.tuna.tsinghua.edu.cn/ubuntu yakkety-security 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 https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/yakkety/main/binary-amd64/Packages  404  Not Found
E: Failed to fetch https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/yakkety-updates/main/binary-amd64/Packages  404  Not Found
E: Failed to fetch https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/yakkety-backports/main/binary-amd64/Packages  404  Not Found
E: Failed to fetch https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/yakkety-security/main/binary-amd64/Packages  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.