function installVPN(){
        echo "begin to install VPN services";
        #check wether vps suppot ppp and tun

        yum remove -y pptpd ppp
        iptables --flush POSTROUTING --table nat
        iptables --flush FORWARD
        rm -rf /etc/pptpd.conf
        rm -rf /etc/ppp

        arch=`uname -m`

        wget http://www.hi-vps.com/downloads/dkms-
        wget http://wty.name/linux/sources/kernel_ppp_mppe-1.0.2-3dkms.noarch.rpm
        wget http://www.hi-vps.com/downloads/kernel_ppp_mppe-1.0.2-3dkms.noarch.rpm
        wget http://www.hi-vps.com/downloads/pptpd-1.3.4-2.el6.$arch.rpm
        wget http://www.hi-vps.com/downloads/ppp-2.4.5-17.0.rhel6.$arch.rpm

        yum -y install make libpcap iptables gcc-c++ logrotate tar cpio perl pam tcp_wrappers
        rpm -ivh dkms-
        rpm -ivh kernel_ppp_mppe-1.0.2-3dkms.noarch.rpm
        rpm -qa kernel_ppp_mppe
        rpm -Uvh ppp-2.4.5-17.0.rhel6.$arch.rpm
        rpm -ivh pptpd-1.3.4-2.el6.$arch.rpm

        mknod /dev/ppp c 108 0 
        echo 1 > /proc/sys/net/ipv4/ip_forward 
        echo "mknod /dev/ppp c 108 0" >> /etc/rc.local
        echo "echo 1 > /proc/sys/net/ipv4/ip_forward" >> /etc/rc.local
        echo "localip" >> /etc/pptpd.conf
        echo "remoteip" >> /etc/pptpd.conf
        echo "ms-dns" >> /etc/ppp/options.pptpd
        echo "ms-dns" >> /etc/ppp/options.pptpd

        pass=`openssl rand 6 -base64`
        if [ "$1" != "" ]
        then pass=$1

        echo "vpn pptpd ${pass} *" >> /etc/ppp/chap-secrets

        iptables -t nat -A POSTROUTING -s -j SNAT --to-source `ifconfig  | grep 'inet addr:'| grep -v '' | cut -d: -f2 | awk 'NR==1 { print $1}'`
        iptables -A FORWARD -p tcp --syn -s -j TCPMSS --set-mss 1356
        service iptables save

        chkconfig iptables on
        chkconfig pptpd on

        service iptables start
        service pptpd start

        echo "VPN service is installed, your VPN username is vpn, VPN password is ${pass}"


function repaireVPN(){
        echo "begin to repaire VPN";
        mknod /dev/ppp c 108 0
        service iptables restart
        service pptpd start

function addVPNuser(){
        echo "input user name:"
        read username
        echo "input password:"
        read userpassword
        echo "${username} pptpd ${userpassword} *" >> /etc/ppp/chap-secrets
        service iptables restart
        service pptpd start

echo "which do you want to?input the number."
echo "1. install VPN service"
echo "2. repaire VPN service"
echo "3. add VPN user"
read num

case "$num" in
[1] ) (installVPN);;
[2] ) (repaireVPN);;
[3] ) (addVPNuser);;
*) echo "nothing,exit";;