After issued command to stop pptpd, the pptpd won't stop until all the VPN client has disconnected. The following code shows pptpd is still running after issuing the stop command.

ubuntu@ip-10-138-31-87:~$ sudo /etc/init.d/pptpd stop
Stopping PPTP: pptpd.
ubuntu@ip-10-138-31-87:~$ ps -ef |grep pptpd
root      5524     1  0 21:46 ?        00:00:00 pptpd [<myIp>:8544 - 0000]                                                                                                 
root      5525  5524  0 21:46 pts/1    00:00:00 /usr/sbin/pppd local file /etc/ppp/pptpd-options 115200 192.168.0.1:192.168.0.234 ipparam <myIP> plugin /usr/lib/pptpd/pptpd-logwtmp.so pptpd-original-ip <myIP>
ubuntu    5564  4668  0 21:50 pts/4    00:00:00 grep --color=auto pptpd

After all the active vpn client connections were disconnected mannually, the pptpd then stops. Is there a way that pptpd can be forced to stop even there are active vpn client connections?