VPS换成了Debian9，运行curl的时候提示：
-bash: curl: command not found
运行 sudo apt-get install curl 结果被告知sudo命令也未找到：
-bash: sudo: command not found
运行 apt-get install curl 结果又提示 404 Not Found 的错误：
Reading package lists… Done
Building dependency tree
Reading state information… Done
The following additional packages will be installed:
libcurl4
The following NEW packages will be installed:
curl libcurl4
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 596 kB of archives.
After this operation, 1,123 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Err:1 http://deb.debian.org/debian buster/main amd64 libcurl4 amd64 7.64.0-4
404 Not Found [IP: 151.101.26.132 80]
Err:2 http://deb.debian.org/debian buster/main amd64 curl amd64 7.64.0-4
404 Not Found [IP: 151.101.26.132 80]
E: Failed to fetch http://deb.debian.org/debian/pool/main/c/curl/libcurl4_7.64.0-4_amd64.deb 404 Not Found [IP: 151.101.26.132 80]
E: Failed to fetch http://deb.debian.org/debian/pool/main/c/curl/curl_7.64.0-4_amd64.deb 404 Not Found [IP: 151.101.26.132 80]
E: Unable to fetch some archives, maybe run apt-get update or try with –fix-missing?
运行 apt-get install sudo 依旧是 404 Not Found 的报错：
Reading package lists… Done
Building dependency tree
Reading state information… Done
The following package was automatically installed and is no longer required:
grub-pc-bin
Use ‘apt autoremove’ to remove it.
The following NEW packages will be installed:
sudo
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 1,055 kB of archives.
After this operation, 3,108 kB of additional disk space will be used.
Err:1 http://deb.debian.org/debian stretch/main amd64 sudo amd64 1.8.19p1-2.1
404 Not Found [IP: 146.75.94.132 80]
E: Failed to fetch http://deb.debian.org/debian/pool/main/s/sudo/sudo_1.8.19p1-2.1_amd64.deb 404 Not Found [IP: 146.75.94.132 80]
E: Unable to fetch some archives, maybe run apt-get update or try with –fix-missing?
ping了一下 deb.debian.org 发现是可以正常解析的，所以应该排除是dns的问题
于是尝试 apt-get update 之后再运行 apt-get install sudo 问题解决（curl同理）
如还不能解决问题的朋友可以尝试 apt update 以及 sudo apt upgrade
