Linux Know-How provides a collection of introductory texts on often needed Linux skills.

Access from the outside world

The only difficulty is that your IP address is dynamically allocated to you by your Internet Service Provider (ISP) from their IP address pool, and therefore the IP address is not the same every time you connect (unless you made specific arrangements with your ISP). To telnet, ftp, or access your web pages (served by your appache web server) from the outside world, one has to know your current IP address. To find out my current IP address, I use this "interface configuration" command which, when run without any parameters, just displays info on all active network interfaces present on your machine:


On my machine this displays three paragraphs of information on: eth0 (the first ethernet network interface that leads to other computers on my home network), lo (the loopback-only interface, the one with IP, this one must be present on every machine), and ppp0 (the first point-to-point protocol interface). My current IP address, assigned to me by my ISP, is displayed under the ppp0 heading. (Your Linux machine can have multiple IP addresses assigned at the same time, so if you have a "static" IP that you use on your home network, it is still valid but visible only on your home network.)

Once I know the IP address, I can send it through ICQ or e-mail to a friend, who can then, for example, telnet or ftp my computer (s/he must have an account on my machine) and run a program on my Linux machine, or enter http://my_ip_address on the "location" line in the browser to browse my home web pages, etc. If the friend has Xwindows on his/her local machine, s/he can even run a GUI program on a my server and direct the display on his computer.

I can also write a short script that will automatically notify my friend when I am connecting to the Internet and enter the name of the script under kppp-setup-account-edit-dial-"execute program upon connect". Here is my script which notifies me at work when somebody in my house is going on-line (I entered the text into a text file and made the file executable using chmod o+x file_name) :


sleep 15

/sbin/ifconfig | mail -s notification my_email_address

The first line of this script tells my computer to interpret this text file as a bash shell script. The second line makes the script wait 15 seconds (just to make sure that the e-mail is not sent before the ppp connection is fully established). The third line executes the ifconfig command and pipes the output to the mail utility that sends it to my_email_address under the subject "notification".

A more flexible way to access your home computer remotely is to configure it as a dial-up ppp server (as opposed to the dial-in client that you use when you connect to your ISP). If somebody has a simple recipe how to do it, please drop a line.

To summarize, unlike MS Windows 3.x/95/98 which severely restricts traffic to your computer, Linux is very network oriented and it is easy to make all kinds of network connections both FROM and TO your Linux computer. The powerful networking features are generally considered a Linux a strength but, from a real newbie point of view, they can be a problem (see the next question).

Last Update: 2010-12-16