阿里云全新的debian10.3(buster)镜像，却无法正常执行 sudo apt-get update。主要报错信息如下：
Err:6 http://mirrors.cloud.aliyuncs.com/debian buster-backports Release
404 Not Found [IP: 100.100.2.148 80]
Err:3 http://mirrors.cloud.aliyuncs.com/debian buster-proposed-updates InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E98404D386FA1D9 NO_PUBKEY 6ED0E7B82643E131
Reading package lists... Done
E: The repository 'http://mirrors.cloud.aliyuncs.com/debian buster-backports Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://mirrors.cloud.aliyuncs.com/debian buster-proposed-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E98404D386FA1D9 NO_PUBKEY 6ED0E7B82643E131
E: The repository 'http://mirrors.cloud.aliyuncs.com/debian buster-proposed-updates InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
1、通过执行 sudo apt-get update | grep "Failed" 捕捉到更精炼的报错信息，我的执行结果如下：
E: The repository 'http://mirrors.cloud.aliyuncs.com/debian buster-backports Release' does not have a Release file.
W: GPG error: http://mirrors.cloud.aliyuncs.com/debian buster-proposed-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E98404D386FA1D9 NO_PUBKEY 6ED0E7B82643E131
E: The repository 'http://mirrors.cloud.aliyuncs.com/debian buster-proposed-updates InRelease' is not signed.
可以发现有两个报错，一个 buster-backports Release 不存在的问题，一个 The following signatures couldn't be verified 的问题
2、首先解决报出的 buster-backports Release 不存在的问题，vi /etc/apt/sources.list一下，编辑 sources.list 文件。将 buster-backports 涉及的两行注释掉
# deb http://mirrors.cloud.aliyuncs.com/debian/ buster-backports main non-free contrib
# deb-src http://mirrors.cloud.aliyuncs.com/debian/ buster-backports main contrib non-free
之后保存并退出。
3、接下来解决 The following signatures couldn't be verified 的问题，直接安装新版本 debian-archive-keyring 即可
sudo apt-get install debian-archive-keyring
4、最后再次执行 sudo apt-get update，执行成功！完美！
附：
1、关于buster-backports：
"buster-backports" 是 Debian 10（也被称为 "buster"）的 backports 仓库。
Backports 是 Debian 提供的一种机制，允许用户从未来的稳定版本（testing 或 unstable）中获取并安装软件包，这些软件包已经被重新编译，以便在当前的稳定版本中使用。
这种机制的主要目的是允许用户在保持系统稳定性的同时，能够使用到更新的软件版本。例如，如果你正在运行 Debian 10（buster），但你需要一个在 Debian 11（bullseye）中可用的更新版本的软件，你可以从 buster-backports 仓库中获取并安装它。
总的来说，http://mirrors.cloud.aliyuncs.com/debian buster-backports Release 的作用是提供一个可以获取并安装更新版本软件包的源，这些软件包是为当前的 Debian 10 系统重新编译的。
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