各类VPN的安装方法
PPTP：
https://effmx.com/articles/zai-vpsshang-da-jian-pptp-vpnde-ji-jian-gong-lue/
https://github.com/teddysun/across/blob/master/pptp.sh
https://github.com/DanylZhang/VPS/blob/master/CentOS-pptp-setup.sh
L2TP/IPSEC:
https://github.com/hwdsl2/setup-ipsec-vpn
https://raw.githubusercontent.com/hwdsl2/setup-ipsec-vpn/master/vpnsetup_centos.sh
https://teddysun.com/448.html
openvpn:
https://github.com/angristan/openvpn-install
https://github.com/Nyr/openvpn-install
wiregrand:
https://github.com/angristan/wireguard-install
https://teddysun.com/554.html