ubuntu16纠结的apt-get update时fail to fetch http:/ ..404 Not Found问题

主要问题:apt-get update
E: Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/main/binary-arm64/Packages 404 Not Found [IP: 91.189.88.152 80]
E: Failed to fetch https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/xenial/main/binary-arm64/Packages 404 Not Found
E: Failed to fetch https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/xenial-updates/main/binary-arm64/Packages 404 Not Found
E: Failed to fetch https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/xenial-backports/main/binary-arm64/Packages 404 Not Found
E: Failed to fetch https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/xenial-security/main/binary-arm64/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.

类似收索如上问题把改国内的源都试遍，而且各DNS也试着改了不少，都照样是fail to fetch: 。所以我用浏览器访问了一下这个网址:https://mirrors.tuna.tsinghua.edu.cn/ubuntu 发现是可以访问的，于是照上面的目录依次往下查找，到http://security.ubuntu.com/ubuntu/dists/xenial-security/main/的时候发现:
Index of /ubuntu/dists/xenial-security/main
[ICO] Name Last modified Size
[PARENTDIR] Parent Directory -
[DIR] binary-amd64/ 2020-06-16 03:59 -
[DIR] binary-i386/ 2020-06-16 03:59 -
在Index of /ubuntu/dists/xenial-security/main这个目录下是没有找到上面update提示的:/binary-arm64 。所以想说这个arm64架构的更新是必要的吗?
1、查看一下本机架构:sudo dpkg --print-architecture 发现本机是amd64架构，那这个arm64应该是当时下其他软件为了支持而添加的。
2、查看外加支持的架构:sudo dpkg --print-foreign-architectures 显示有i386和arm64，这样多架构支持的设置在某些源上可能没有这么全面把。
3、sudo dpkg --remove-architecture arm64 删掉上面网页没有找到的arm64架构
再次查看: sudo dpkg --print-foreign-architectures
i386
4、此时再 sudo apt-get update 就不再报错了