mgetty Command in Linux
mgetty is a Linux command that allows you to manage and control modems on a system. This command allows incoming connection via a serial line and makes it possible for users to dial into the system using modem. mgetty is often used to set up dial-up services, including allowing remote users to log in to the system. It also supports sending and receiving faxes.
This command is particularly useful in environments where legacy communication methods are still in use or for certain specialized applications. It provides a reliable way to handle modem communication and ensure that incoming calls are properly managed and connected.
Table of Contents
Here is a comprehensive guide to the options available with the mgetty command −
- How to Install mgetty Command in Linux
- Syntax of mgetty Command
- mgetty Command Options
- Examples of mgetty Command in Linux
How to Install mgetty Command in Linux?
Linux systems do not come with mgetty preinstalled. You can install it using the package manager available on your system.
For Debian-based systems (like Ubuntu)
sudo apt install mgetty
For Red Hat-based systems (like CentOS)
sudo yum install mgetty
For Arch Linux
sudo pacman -S mgetty
Syntax of mgetty Command
Below is the common syntax for executing the mgetty command in Linux −
mgetty [options]
Where, options are different flags that can be applied to modify the command's execution.
mgetty Command Options
The following table highlights a few of the options that can be applied when using the command mgetty on Linux environment −
| Options | Description |
|---|---|
| -k <space> | Leave <space> kilobytes free on disk when receiving a fax. |
| -x <debug level> | Set the verbosity level for logging (0 means no logging, 9 is very detailed). Logs are usually stored in /tmp/log_mg.<device>. |
| -s <speed> | Set the port speed, e.g., -s 19200. |
| -r | Indicate that mgetty is running on a direct line with no modem initialization. UUCP locking is still done. |
| -p <login prompt> | Use the specified string to prompt users for their login names, with various tokens for system info. |
| -n # | Pick up the phone after the specified number of rings. Default is 1. |
| -R <t> | Enter "ringback" mode, answering the call only if another call is made within the specified time after the first call is not answered. |
| -i <issue file> | Display the specified issue file before the login prompt instead of /etc/issue, with similar token substitutions as the login prompt. |
| -D | Treat the modem as a data modem only, without attempting fax initialization. |
| -F | Set the modem to fax-only mode, disallowing data calls. |
| -C <class> | Specify how to treat the modem (e.g., auto, cls2, c2.0, data). |
| -S <g3 file> | Send the specified file if a call requests fax polling. |
| -I <fax id> | Use the specified fax station ID for fax identification. |
| -b | Open the port in blocking mode, useful in combination with -r. Default if mgetty is called as getty. |
| -a | Use autobauding, adjusting port speed based on the modem's "CONNECT" response. Generally not recommended; fixing the port speed is preferred. |
| -m 'expect send ...' | Set the chat sequence for modem initialization, using expect/send strings. Example: mgetty -m '"" ATH0 OK'. |
Examples of mgetty Command in Linux
The following are a few scenarios showcasing the usage of the Linux mgetty command −
- Running mgetty as a Daemon
- Setting a Custom Login Prompt
- Running on a Direct Line
- Specifying Port Speed
- Setting the Number of Rings Before Answering
- Enabling Autobauding
Running mgetty as a Daemon
To have mgetty run continuously in the background and manage the modem without occupying your terminal, use the -D option −
sudo mgetty -D /dev/ttyS0
In this example, mgetty will monitor the modem connected to /dev/ttyS0 and handle incoming connections in the background, freeing up your terminal for other tasks.
Setting a Custom Login Prompt
You can personalize the login prompt that users see when they connect via the modem by using the -p option followed by your custom message −
sudo mgetty -p "Welcome to MySystem, please login: " /dev/ttyS0
This command makes the login prompt display "Welcome to MySystem, please login:" when users access your system through the modem on port /dev/ttyS0, adding a personalized touch to the login process.
Running on a Direct Line
If your modem is connected directly without needing initialization, you can use the -r option to bypass the initialization steps −
sudo mgetty -r /dev/ttyS0
This command configures mgetty to operate on a direct line for the modem on /dev/ttyS0, simplifying the setup by avoiding unnecessary initialization sequences.
Specifying Port Speed
To set the communication speed of the modem, use the -s option followed by the desired baud rate −
sudo mgetty -s 19200 /dev/ttyS0
This command configures the modem on /dev/ttyS0 to communicate at a speed of 19200 baud, ensuring that the data transfer rate meets your requirements.
Setting the Number of Rings Before Answering
You can control how many times the phone should ring before mgetty picks up by using the -n option −
sudo mgetty -n 3 /dev/ttyS0
This command tells mgetty to answer incoming calls after the third ring on port /dev/ttyS0, which can be useful to distinguish between voice and data calls or to avoid premature answering.
Enabling Autobauding
To automatically adjust the port speed based on the modem's connection response, use the -a option −
sudo mgetty -a /dev/ttyS0
This command enables mgetty to dynamically set the port speed according to the modem's "CONNECT" response on /dev/ttyS0, adapting to varying connection speed.
Conclusion
The mgetty is a powerful command for managing modems on Linux systems, offering a range of options to customize its behavior to meet your specific needs.
Whether it's setting custom login prompts, handling fax communications, or running as a background daemon, mgetty provides flexibility and control over modem operations. Understanding these examples will help you effectively use mgetty for various applications.