If your OS is CentOS/RedHat 5:

yum install ppp
cd /usr/local/src
wget http://poptop.sourceforge.net/yum/stable/packages/pptpd-1.3.4-2.rhel5.x86_64.rpm
rpm -Uhv pptpd-1.3.4-2.rhel5.x86_64.rpm

If your OS is CentOS/RedHat 6:

yum install ppp
cd /usr/local/src
wget http://poptop.sourceforge.net/yum/stable/packages/pptpd-1.3.4-2.el6.x86_64.rpm
rpm -Uhv pptpd-1.3.4-2.el6.x86_64.rpm

If you are using Ubuntu:

apt-get install pptpd

Step 2. Edit IP setttings in /etc/pptpd.conf

vi /etc/pptpd.conf

localip 192.168.0.1
remoteip 192.168.0.101-200

Step 3. Add user account in/etc/ppp/chap-secrets (assign username and password)

vi /etc/ppp/chap-secrets

usernameForuser1 *  setpassword1here  *

usernameForuser2 *  setpassword2here  *

Step 4. Optional settings in /etc/ppp/options.pptpd

vi /etc/ppp/options.pptpd

ms-dns 8.8.8.8
ms-dns 4.4.4.4

Step 5. Enable network forwarding in /etc/sysctl.conf
vi /etc/sysctl.conf

net.ipv4.ip_forward = 1

use the following command to apply the change:

sysctl -p

Step 6. Configure firewall

iptables -A INPUT -i eth0 -p tcp --dport 1723 -j ACCEPT
iptables -A INPUT -i eth0 -p gre -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i ppp+ -o eth0 -j ACCEPT
iptables -A FORWARD -i eth0 -o ppp+ -j ACCEPT
service iptables save
service iptables restart
If you are using CSF firewall, you may refer to this post on firewall settings.

Step 7. Start PPTP VPN server

If your OS is CentOS or Redhat, using the following command:

service pptpd restart

To start PPTP Daemon automatically when rebooting next time, use command:

chkconfig pptpd on

If your OS is Ubuntu, you just reboot your machine.

Now you can test the VPN server from any client: Windows PCs, Linux PCs, Android phones/tablets, or iPhone and iPad.

The log of the VPN server, by default, is combined with system log located at /var/log/messages.