一、备份现有apt源配置

mv /etc/apt/sources.list /etc/apt/sources.list.old

二、替换为其他apt源

1、替换为默认官方源

cat > /etc/apt/sources.list << EOF
deb https://deb.debian.org/debian/ bullseye main contrib non-free
deb-src https://deb.debian.org/debian/ bullseye main contrib non-free

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

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

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

2、替换为中科大源

cat > /etc/apt/sources.list << EOF
deb https://mirrors.ustc.edu.cn/debian/ bullseye main contrib non-free
deb-src https://mirrors.ustc.edu.cn/debian/ bullseye main contrib non-free

deb https://mirrors.ustc.edu.cn/debian/ bullseye-updates main contrib non-free
deb-src https://mirrors.ustc.edu.cn/debian/ bullseye-updates main contrib non-free

deb https://mirrors.ustc.edu.cn/debian/ bullseye-backports main contrib non-free
deb-src https://mirrors.ustc.edu.cn/debian/ bullseye-backports main contrib non-free

deb https://mirrors.ustc.edu.cn/debian-security/ bullseye-security main contrib non-free
deb-src https://mirrors.ustc.edu.cn/debian-security/ bullseye-security main contrib non-free
EOF

三、更新apt索引

apt update