Many users connect to the Internet via modem lines. Modem connections usually use the Point-to-Point Protocol (PPP) to connect computers with their Internet Service Provider (ISP). Before you connect to the Internet, you must set up Linux to find your modem.
Linux needs to know which serial port a modem uses. You do this by setting a logical link that points to the correct device file. Red Hat Linux provides modemtool, a GUI tool that makes this procedure easier. You simply select the port you wish to use and click OK. The image below shows you the modemtool interface.
Using the command line method
You can also set the logical link by issuing the ln -s command from a prompt.
For example, to set /dev/modem to use the port /dev/ttyS0 you could execute ln -s /dev/ttyS0 /dev/modem as root.
The next lesson shows you how to configure a PPP connection with RP3.
Logical link: A type of file that is a reference to another real file.