禁用 IPv6 解析
Convince apt-get *not* to use IPv6 method – Unix & Linux Stack Exchange
echo 'Acquire::ForceIPv4 "true";' | tee /etc/apt/apt.conf.d/99-force-ipv4
或者，使用 apt-get -o Acquire::ForceIPv4=true 选项
代理服务，加速下载
syntax for SOCKS proxy in apt.conf
How to use “apt-get” via “Http-proxy” like this?
man 5 apt.conf
man apt-transport-http
man apt-transport-https
有时需要使用 SOCKS/HTTP(S) 代理进行软件包下载，以提高网络下载速度。
操作系统：Kali GNU/Linux Rolling / apt 1.8.4 (amd64)
方法一、创建 /etc/apt/apt.conf.d/99socks.conf 配置：
cat > /etc/apt/apt.conf.d/99socks.conf <<EOF Acquire::http::proxy "socks5h://127.0.0.1:1080"; EOF
方法二、命令行指定（推荐）
http_proxy='http://127.0.0.1:8123' apt-get update
注意事项，应该使用 http_proxy，而不是 HTTP_PROXY 变量。
附加说明
Differentiate socks5h from socks5 and socks4a from socks4 when handling proxy string #1035
In a proxy string,
socks5h:// and socks4a:// mean that the hostname is resolved by the SOCKS server.
socks5:// and socks4:// mean that the hostname is resolved locally.
socks4a:// means to use SOCKS4a, which is an extension of SOCKS4.