如果想换源，执行 cat /dev/null > /etc/apt/sources.list 后再自行加源
清华源：
cat > /etc/apt/sources.list <<EOF
deb https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye main contrib non-free
deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye main contrib non-free
deb https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-updates main contrib non-free
deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-updates main contrib non-free
deb https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-backports main contrib non-free
deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-backports main contrib non-free
deb https://mirrors.tuna.tsinghua.edu.cn/debian-security bullseye-security main contrib non-free
deb-src https://mirrors.tuna.tsinghua.edu.cn/debian-security bullseye-security main contrib non-free
EOF
阿里源：
cat > /etc/apt/sources.list <<EOF
deb http://mirrors.aliyun.com/debian/ bullseye main non-free contrib
deb http://mirrors.aliyun.com/debian/ bullseye-updates main non-free contrib
deb http://mirrors.aliyun.com/debian/ bullseye-backports main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ bullseye main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ bullseye-updates main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ bullseye-backports main non-free contrib
deb http://mirrors.aliyun.com/debian-security/ bullseye-security main non-free contrib
deb-src http://mirrors.aliyun.com/debian-security/ bullseye-security main non-free contrib
EOF
华为源：
cat > /etc/apt/sources.list <<EOF
deb https://mirrors.huaweicloud.com/debian/ buster main contrib non-free
deb https://mirrors.huaweicloud.com/debian/ buster-updates main contrib non-free
deb https://mirrors.huaweicloud.com/debian/ buster-backports main contrib non-free
deb https://mirrors.huaweicloud.com/debian-security/ buster/updates main contrib non-free
deb-src https://mirrors.huaweicloud.com/debian/ buster main contrib non-free
deb-src https://mirrors.huaweicloud.com/debian/ buster-updates main contrib non-free
deb-src https://mirrors.huaweicloud.com/debian/ buster-backports main contrib non-free
EOF
中科大源：
cat > /etc/apt/sources.list <<EOF
deb https://mirrors.ustc.edu.cn/debian/ buster main contrib non-free
deb https://mirrors.ustc.edu.cn/debian/ buster-updates main contrib non-free
deb https://mirrors.ustc.edu.cn/debian/ buster-backports main contrib non-free
deb https://mirrors.ustc.edu.cn/debian-security/ buster/updates main contrib non-free
deb-src https://mirrors.ustc.edu.cn/debian/ buster main contrib non-free
deb-src https://mirrors.ustc.edu.cn/debian/ buster-updates main contrib non-free
deb-src https://mirrors.ustc.edu.cn/debian/ buster-backports main contrib non-free
deb-src https://mirrors.ustc.edu.cn/debian-security/ buster/updates main contrib non-free
EOF
更新
apt-get update
apt-get upgrade清华源无ssl
cat > /etc/apt/sources.list <<EOF
deb http://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye main contrib non-free
deb-src http://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye main contrib non-free
deb http://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-updates main contrib non-free
deb-src http://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-updates main contrib non-free
deb http://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-backports main contrib non-free
deb-src http://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-backports main contrib non-free
deb http://mirrors.tuna.tsinghua.edu.cn/debian-security bullseye-security main contrib non-free
deb-src http://mirrors.tuna.tsinghua.edu.cn/debian-security bullseye-security main contrib non-free
EOF