[Chapter 12] 12.5 Configuring a Dial-In Shell Server

12.5 Configuring a Dial-In Shell Server

A dial-in server lets you connect to a system via a modem and phone line, and obtain a shell prompt, from which you can issue commands and view output. Using a dial-in server is a great deal like using Telnet or a secure shell server, except that your connection to the server is via a phone line. The mgetty package provides a simple-to-use dial-in server.

12.5.1 Configuration

To configure mgetty to answer incoming modem calls, use your favorite text editor to find the following lines in the file /etc/inittab:

 # Example how to put a getty on a modem line # #T3:23:respawn:/sbin/mgetty -x0 -s 57600 ttyS3

Then, modify the last line by deleting the hash mark (#) and changing ttyS3 to modem:

 T3:23:respawn:/sbin/mgetty -x0 -s 57600 modem

Notice that the revised line invokes mgetty, not getty. The final argument specified on the added line assumes that your modem is configured as /dev/modem. If your modem is configured as a different device, you must adjust the added line accordingly. The Chapter 11, Getting Connected to the Internet described the use of modemtool to configure your modem; if you followed its instructions, /dev/modem refers to your modem.

To cause your configuration change to take effect, you must reboot your system. Alternatively, you can cause the init process to re-examine the inittab file. To do so, issue the following command:

 /sbin/telinit q

The mgetty process should begin monitoring your modem, awaiting an incoming call.

12.5.2 Using the Dial-In Server

To use the dial-in server, launch a program such as Microsoft Windows' Hyperterminal and place a call to the phone line to which your Linux system's modem is connected. Your Linux system should answer the call and provide you with a login prompt. Respond with your userid and password and you should receive a shell prompt, at which you can enter commands and view their output.

If you have only a single phone line, you'll be unable to place a call to your Linux system. You'll have to call from some other location.