"Linux Gazette...making Linux just a little more fun!"

Running Your Own Domain Over a Part Time Dialup

By Joe Merlino

You love your linux box. You love the power. You love the flexability. You love the freedom. You really love the utter non-microsoftness of it. But deep down inside, you know there's something missing. A deep longing sits within you, crying out to be assuaged.

Your friends with full-time ethernet connections have it. Your really rich friend with a T-1 to the house has it. They can log into their linux boxen any time they want. They have their own domain names. You probably even have an account on one of their machines. But look what you're stuck with. Sure your modem's pretty fast, but it only dials up when you tell it to, and you can't tell it when you're not logged in. Even if you set it up to run as a cron job, you wouldn't know where to telnet to because your ISP gives you a different IP number every time you dial in.

How do you get remote access?

Fear not. There Is A Way. For the price of a dialup PPP account, you can have that precious remote access. And if you're willing to pay the freight to InterNIC (you can scrape up seventy bucks, can't you?) you can even have your own domain. Here's how:


The general setup of PPP connections on Linux is well documented elsewhere, so I won't go into it, except to say that you need to have PPP set up to run non-interactively from a command line. Graphical programs to activate PPP such as EZPPP or Red Hat's netcfg won't work. This is because you're going to create a script to be run as a cron job, and that script needs to be able to call your PPP-connecting script.

For the purposes of this article, my PPP-connecting script is called /etc/ppp/ppp-on, and the script that ends the PPP connection is called /etc/ppp/ppp-off. You should be able to find examples of these sorts of scrips on the web.


You probably have Domain Name Service (DNS) through your ISP, but your ISP doesn't keep track of your particular connection because it changes every time you dial in. Your ISP does this because it has more users than it does IP numbers. This makes sense when you consider that most of the people who use the service only connect for a short time - a couple of hours at most. You can probably get a full-time connection and a static IP number from your ISP, but such things are typically pretty expensive.

The thing is, you don't really need a static IP number to have a constant domain name. As long as the Domain Name Server where your domain name lives knows what your IP number is *at any given time*, you can get to your machine. And the DNS server where you domain name lives doesn't have to be the same one that belongs to your ISP.

I use a service provided by a company called Dyndns (www.dyndns.com) Dyndns will, for a fee, maintain your domain name in its database. The domain name you get can either be a subdomain of theirs (i.e. yourdomain.dyndns.com), which is cheaper, or your can have your own unique domain name (i.e. yourdomain.com), which is somewhat more expensive. If you want a unique domain name, irst, you have to register your domain name with InterNIC (www.internic.net). Dyndns will do this for you, for a fee, but it's so easy to do, you might as well save yourself the money and do it yourself. When you register with InterNIC, you have to supply the IP numbers of a primary and secondary DNS server. These numbers are available on Dyndns's web page. Once all of this goes through (read: is paid for), you're good to go.

The next thing you do is download a client program from Dyndns's website. They have a couple of different clients you can choose from (one in C, and one in Perl), and it might take some experimenting to figure out which one is better for you (even then, I had to have a friend of mine hack the Perl client a little to make it work).

When you are logged into your ISP, you run the client program. The client program gets your current IP number from the output of the 'ifconfig' command, and reports it to Dyndns's DNS server. Your domain name is now pointed at your machine.

[Note: Nothing I've said in this section should be considered an endorsement of or advertisement for Dyndns. I've used their service as an example because it's the service I use, and it's what I'm familiar with.]


You've got the domain name, you've got the DNS service, amd you've got the client program working. Now you need a way to make the computer log itself onto your ISP without your actually being there to do it. Ah, the wonders of Linux! This is taken care of with a simple shell script. Here's what I use:


#  This is a script that attempts to log into a remote dialup and
#  establish a PPP connection. If it is sucessful, it runs 'ntpdate'
#  (network clock set), NamedControl.pl (a perl script to update
#  the dynamic DNS), and fetchmail for all accounts. If it fails, it
#  makes two more attempts, and then exits.

#  This script is released under the GNU General Public Licence. No
#  warrenty whatsoever is expressed or implied.

#  Original version was written by Joe Merlino <joe@negia.net>, November,
#  1997.

#  If you have an idea for an improvement to this script, please let me
#  know. 

#  set iteration counter at 1
while [ $i -le 3 ]

    #  This part tests for the availability of the modem. If the modem
    #  is available, it runs /etc/ppp/ppp-on. If not, it reports and
    #  exits.

    if (test -e /var/lock/LCK..modem)
        echo modem not available  # for some reason this didn't work. 
        exit 0
        sleep 45

    #  This part tests for the modem lock file, and if it exists, runs
    #  the various programs needed to update the system from the network.
    #  if the lock file is not found, it reports and exits.

    if (test -e /var/lock/LCK..modem)
        /etc/ppp/netpack  #invoke 'netpack' script
        echo done
       echo no connection
    sleep 60

      #  This part again tests for the lock file, and if it finds it, sets
      #  the iteration counter to 4 (so the script will exit). If the lock
      #  file is not found, it incriments the counter by one.

      if (test -e /var/lock/LCK..modem)
      i=`expr $i + 1`
      echo $i
You'll notice that this script calls another script, 'netpack'. I've done that because I have a set of things I like to do when my machine logs itself in. At the very least, 'netpack' should include your dynamic DNS client script. I would also recommend that it include whatever you use to download your email (e.g. 'fetchmail' or 'popclient' or whatever). It would also be possible to replace the line that calls 'netpack' with a series of lines that call the various programs, but I like the modular design because I can edit 'netpack' on it's own.

I put both this script (which I named 'auto-up'), and 'netpack' in /etc/ppp/.

Once you've got all that set up, try running it manually to make sure it works. (Don't forget to give yourself execute permission.) Once you've established that it works, set it up as a cron job (using the 'crontab -e' command) to run whenever you want to have remote access to your linux box. Also, set up /etc/ppp/ppp-off to run when you want your access to end.

[Note: Some ISPs have a limit on the amount of time you can be connected without doing anything. This is to keep people from logging in and simply leaving their computers connected indefinitely. You should be aware of your ISP's policy with regard to this.]

And there it is. You now have remote access to your machine at specified times. Now you can start pining for a full-time connection.

Addendum: Between the time I wrote this article, and the time that this issue of Linux Gazette was posted, DynDNS added a web-based update system to its already existing methods. This means that you can update DynDNS manually, with your browser.

It also gives us the opportunity to write another Perl client. This one can be much more compact, and should work "out of the box" with only one small hack required for your account information.

If you want to use it, simply copy the text between the ---CUT--- lines to a file, give yourself execute permission, and use it in place of the other client program.



# Client script for HTTP update of DynDNS's Dynamic Domain service.
# Written by Joe Merlino  12/31/98
# Licence: GNU GPL

use IO::Socket;

# Replace the values below with your information as indicated

$host = "master.dyndns.com";
$myhost = "myhost";		#replace with your hostname
$myname = "postmaster";		
$mypass = "mypass";		#replace with your password

# This part opens a connection to DynDNS's web server.
$remote = IO::Socket::INET->new(
	Proto => "tcp",
	PeerAddr => "$host",
	PeerPort => "http(80)"
	or die "couldn't open $host";

# This part sends an HTTP request containing your information.
print $remote "GET /dyndns/cgi/DynDNSWeb.cgi?name=$myname&passwd=$mypass&domain=$myhost&IP=AUTO HTTP/1.0\n\n";

#This part extracts and prints DynDNS's response.
while ($hrm = <$remote>) {

	if ($hrm =~ /UPDATE/) {
		$message = $hrm

	if ($line =~ /THERE/) {
		$message = $hrm

print "DynDNS: $message";

-close $remote;

Copyright © 1999, Joe Merlino
Published in Issue 36 of Linux Gazette, January 1999