国外的服务器升级操作，源部分国内麻烦自行更换。

1、编辑源地址

nano /etc/apt/sources.list

加入下面的源：

deb http://deb.debian.org/debian bullseye main
deb-src http://deb.debian.org/debian bullseye main

deb http://deb.debian.org/debian-security/ bullseye-security main
deb-src http://deb.debian.org/debian-security/ bullseye-security main

deb http://deb.debian.org/debian bullseye-updates main
deb-src http://deb.debian.org/debian bullseye-updates main

保存退出后：

apt update

apt dist-upgrade

然后重启一下就行了。

reboot

其他国外可用的debian11源

deb http://deb.debian.org/debian bullseye main contrib non-free
deb-src http://deb.debian.org/debian bullseye main contrib non-free

deb http://deb.debian.org/debian-security/ bullseye-security main contrib non-free
deb-src http://deb.debian.org/debian-security/ bullseye-security main contrib non-free

deb http://deb.debian.org/debian bullseye-updates main contrib non-free
deb-src http://deb.debian.org/debian bullseye-updates main contrib non-free

debian12源

deb http://deb.debian.org/debian bookworm main contrib

deb http://deb.debian.org/debian bookworm-updates main contrib

deb http://security.debian.org bookworm-security main contrib