相关代码如下

#!/bin/bash
#    Setup Simple PPTP VPN server for CentOS
#    Copyright (C) 2015-2016 Danyl Zhang <1475811550@qq.com> and contributors
#
#    This program is free software; you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation; either version 2 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.

#定义帮助信息函数
printhelp() {
echo "
Usage: ./CentOS-pptp-setup.sh [OPTION]
If you are using custom password , Make sure its more than 8 characters. Otherwise it will generate random password for you. 
If you trying set password only. It will generate Default user with Random password. 
example: ./CentOS-pptp-setup.sh -u myusr -p mypass
Use without parameter [ ./CentOS-pptp-setup.sh ] to use default username and Random password
  -u,    --username             Enter the Username
  -p,    --password             Enter the Password
"
}

#对输入信息进行判断
while [ "$1" != "" ]; do
  case "$1" in
    -u    | --username )             NAME=$2; shift 2 ;;
    -p    | --password )             PASS=$2; shift 2 ;;
    -h    | --help )            echo "$(printhelp)"; exit; shift; break ;;
  esac
done

# Check if user is root，脚本必须在root用户下执行
[ $(id -u) != "0" ] && { echo -e "\033[31mError: You must be root to run this script\033[0m"; exit 1; } 

#定义路径，清空显示屏幕
export PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
clear

#如果没有curl，就下载它
[ ! -e '/usr/bin/curl' ] && yum -y install curl

#定义相关变量，下面要用到
VPN_IP=`curl ipv4.icanhazip.com`  #通过curl这个地址，可以获取服务器的出口公网IP
VPN_LOCAL="192.168.2.1"           #pptp服务器端IP,可以设置为服务器上绑定的任意一个IP地址
VPN_REMOTE="192.168.2.10-100"     #客户端成功连接VPN后获取的IP地址范围（可以和pptp服务器在同一内网段内，但是建议不要设置和PPTP服务器内网一样的网段）
clear

#下面要下载一下安装包，在epel源中，需要先确认epel源的配置
if [ -f /etc/redhat-release -a -n "`grep ' 7\.' /etc/redhat-release`" ];then  #判断系统是否为centos7
        #CentOS_REL=7
    if [ ! -e /etc/yum.repos.d/epel.repo ];then
        cat > /etc/yum.repos.d/epel.repo << EOF
[epel]
name=Extra Packages for Enterprise Linux 7 - \$basearch
#baseurl=http://download.fedoraproject.org/pub/epel/7/\$basearch
mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=\$basearch
failovermethod=priority
enabled=1
gpgcheck=0
EOF

fi

        for Package in wget make openssl gcc-c++ ppp pptpd iptables iptables-services #下载指定安装包
        do
                yum -y install $Package
        done
        echo 'net.ipv4.ip_forward = 1' >> /etc/sysctl.conf  #修改转发设置
elif [ -f /etc/redhat-release -a -n "`grep ' 6\.' /etc/redhat-release`" ];then   #如果系统是centos6
        #CentOS_REL=6
        for Package in wget make openssl gcc-c++ iptables ppp 
        do
                yum -y install $Package
        done
    sed -i 's@net.ipv4.ip_forward.*@net.ipv4.ip_forward = 1@g' /etc/sysctl.conf
    rpm -Uvh http://poptop.sourceforge.net/yum/stable/rhel6/pptp-release-current.noarch.rpm
    yum -y install pptpd
else
        echo -e "\033[31mDoes not support this OS, Please contact the author! \033[0m"  #如果是其他系统就提醒并退出
        exit 1
fi

sysctl -p  #使转发设置生效

#-z检查/etc/pptpf.conf中相关参数是否已经设置了,然后把设置的相关参数导入到/etc/pptpd.conf中
[ -z "`grep '^localip' /etc/pptpd.conf`" ] && echo "localip $VPN_LOCAL" >> /etc/pptpd.conf # Local IP address of your VPN server
[ -z "`grep '^remoteip' /etc/pptpd.conf`" ] && echo "remoteip $VPN_REMOTE" >> /etc/pptpd.conf # Scope for your home network

#检查并设置dns服务器
if [ -z "`grep '^ms-dns' /etc/ppp/options.pptpd`" ];then
    echo "ms-dns 8.8.8.8" >> /etc/ppp/options.pptpd
    echo "ms-dns 209.244.0.3" >> /etc/ppp/options.pptpd
fi

#no liI10oO chars in password

LEN=$(echo ${#PASS})  #检查密码是否设置

if [ -z "$PASS" ] || [ $LEN -lt 8 ] || [ -z "$NAME"]  
#如果密码字符串为0（就是没有设置）或小于8位或跟要设置的用户名相同，那么就重新设置
then
   P1=`cat /dev/urandom | tr -cd abcdefghjkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789 | head -c 3`
   P2=`cat /dev/urandom | tr -cd abcdefghjkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789 | head -c 3`
   P3=`cat /dev/urandom | tr -cd abcdefghjkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789 | head -c 3`
   PASS="$P1-$P2-$P3"  #生成一个11位的随机密码
fi

if [ -z "$NAME" ]
then
   NAME="vpn"   #如果用户名没有设置，就默认为vpn
fi

cat >> /etc/ppp/chap-secrets <<END  #将账号密码导出到/etc/ppp/chap-secrets中
$NAME pptpd $PASS *
END

ETH=`route | grep default | awk '{print $NF}'`   #获取默认的出口网卡名

#设置iptables规则
[ -z "`grep '1723 -j ACCEPT' /etc/sysconfig/iptables`" ] && iptables -I INPUT 4 -p tcp -m state --state NEW -m tcp --dport 1723 -j ACCEPT  #打开1723端口
[ -z "`grep 'gre -j ACCEPT' /etc/sysconfig/iptables`" ] && iptables -I INPUT 5 -p gre -j ACCEPT   #放行gre隧道连接
iptables -t nat -A POSTROUTING -o $ETH -j MASQUERADE
iptables -I FORWARD -p tcp --syn -i ppp+ -j TCPMSS --set-mss 1356

#保存刚才设置的iptables规则，注释掉（删除）相关规则
service iptables save
sed -i 's@^-A INPUT -j REJECT --reject-with icmp-host-prohibited@#-A INPUT -j REJECT --reject-with icmp-host-prohibited@' /etc/sysconfig/iptables 
sed -i 's@^-A FORWARD -j REJECT --reject-with icmp-host-prohibited@#-A FORWARD -j REJECT --reject-with icmp-host-prohibited@' /etc/sysconfig/iptables 

#设置iptables服务重启，开机运行
service iptables restart
chkconfig iptables on

#设置pptpd服务重启，开机运行
service pptpd restart
chkconfig pptpd on
clear

echo -e "You can now connect to your VPN via your external IP \033[32m${VPN_IP}\033[0m"

echo -e "Username: \033[32m${NAME}\033[0m"
echo -e "Password: \033[32m${PASS}\033[0m"

脚本里面的注释内容有一些是我自己加进去的，方便理解。在使用的时候可以直接用wget下载，或者直接去原地址copy

参考地址：  - Centos7搭建pptp VPN一键安装脚本  - CentOS 7 安装VPN Server 和 Client  - Centos下PPTP环境部署记录  - 如何在windows上配置连接pptpd

脚本在github上的地址：https://github.com/DanylZhang/VPS/blob/master/CentOS-pptp-setup.sh  亲测可用，可以放心用啊。