18. pptp Server Administration

This section covers a few tricks on pptp server management. It is far from a complete guide. Any suggestions are welcome.

The packages psacct and SysVinit are required for the utilities used in here. They should be installed by default. If they are not, please install them through yum.

>     [root@pptp ~]# yum install psacct SysVinit

18.1 Who is Online?

To check who is online, the "last" command is used:

>     [root@pptp ~]# last | grep ppp | grep still
>     James    ppp3         202.xx.xxx.xxx   Sat Nov 19 17:38   still logged in
>     Andrew   ppp1         220.xxx.xxx.xx   Sat Nov 19 17:23   still logged in
>     Mary     ppp2         1.2.3.4          Sat Nov 19 16:59   still logged in
>     Sue      ppp0         202.xx.xxx.xxx   Sat Nov 19 16:43   still logged in
>     Mark     ppp7         203.xxx.xxx.xxx  Sat Nov 19 14:59   still logged in

last is from SysVinit. It reads the information from /var/log/wtmp.

Note: for last to work properly, the logwtmp option in the /etc/pptpd.conf must be enabled. If you are sure there are pptp connections but see no output from the above mentioned command, check the logwtmp option in the pptpd.conf file is enabled.

18.2 Accounting

The "ac" utility from package psacct will provide a report on the connection time.

>     [root@pptp ~]# ac -d -p
>             Amy                                  3.77
>             George                               0.08
>             Mark                                 1.78
>             Richard                              0.35
>             Lee                                  3.66
>             Simon                                5.78
>             Nicole                               1.05
>     Nov  1  total       16.46
>             Amy                                  2.43
>             Nicole                               8.61
>             Richard                              4.77
>             Mark                                 0.90
>             Lee                                  4.68
>             Keith                                1.84
>     Nov  2  total       23.23

The ac command reads the information from /var/log/wtmp. It has a lot of options. Read the man page for details.

Note:
1. If you want the statistics from older version of wtmp, use the -f parameter in "ac" to specify the file.
2. If users use shell to log in the server as well, the ac will return the connection time of both pptp and shell connections.

18.3 Disconnect a User

To disconnect an active connection, you will have to kill the pppd process associate with it. Firstly, run the command in section 16.1 to find out the remote ip address of the user. Say you want to disconnect Mary, her ip address in the above example is 1.2.3.4. Then, find the PID of the pppd process.

>     [root@pptp /]# ps -ef | grep 1.2.3.4 | grep pppd
>     root   8672  8671  0 16:59 ?      00:00:00 /usr/sbin/pppd local file /etc/ppp/options.pptpd 115200
>                                                    10.0.0.10:10.0.0.124 ipparam 1.2.3.4.
>                                                    plugin /usr/lib/pptpd/pptpd-logwtmp.so
>                                                    pptpd-original-ip 1.2.3.4

The second field of the output, 8672 in our example, is the PID of the pppd process. Kill the process will disconnect the user.

>     [root@pptp /]# kill 8672

18.4 Allow Only One Connection per User

By default, a user can make multiple connections to the pptpd server. To restrict one connection per user, create two script files in the /etc/ppp directory. When the same user logs in twice, the first connection will be disconnected. This is actually done on the ppp level, not with the pptpd.

The first file is /etc/ppp/auth-up

>       #!/bin/sh
>       # get the username/ppp line number from the parameters
>       PPPLINE=$1
>       USER=$2
>       # create the directory to keep pid files per user
>       mkdir -p /var/run/pptpd-users
>       # if there is a session already for this user, terminate the old one
>       if [ -f /var/run/pptpd-users/$USER ]; then
>         kill -HUP `cat /var/run/pptpd-users/$USER`
>         rm /var/run/pptpd-users/$USER
>       fi
>       # write down the username in the ppp line file
>       echo $USER > /var/run/pptpd-users/$PPPLINE.new

The second file is /etc/ppp/ip-up.local

>       #!/bin/sh
>       REALDEVICE=$1
>       # Get the username from the ppp line record file
>       USER=`cat /var/run/pptpd-users/$REALDEVICE.new`
>       # Copy the ppp line pid
>       cp "/var/run/$REALDEVICE.pid" /var/run/pptpd-users/$USER
>       # remove the ppp line record file
>       rm "/var/run/pptpd-users/$REALDEVICE.new"

The method presented here may not be the best one, but it works for me. (If you have a better way, please let me know.)

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