Hey guys! Ever needed to figure out which COM ports are available on your Linux machine? Whether you're connecting serial devices, debugging hardware, or just tinkering around, knowing how to list those ports is super handy. Let's dive into a few straightforward methods to get the job done.

Why You Need to Check COM Ports

Before we jump into the how-to, let's quickly cover why you might need to do this. COM ports, or serial ports, are still used for a variety of devices. Think of things like:

• Legacy Hardware: Older printers, scientific instruments, and industrial equipment often use serial connections.
• Embedded Systems: If you're working with microcontrollers or other embedded devices, you'll likely use a serial port for communication and debugging.
• Hobby Projects: Connecting Arduinos, Raspberry Pis, and other DIY gadgets often involves serial communication.
• GPS Devices: Some GPS units communicate via serial ports.

Knowing which ports are available and active helps you configure your software correctly and troubleshoot any connection issues. So, without further ado, let's explore the ways to check those ports.

Method 1: Using ls /dev/tty*

The simplest and most common way to list available COM ports is by using the ls command in the /dev directory. In Linux, device files are stored in the /dev directory, and serial ports typically have names like ttyS0, ttyUSB0, ttyACM0, etc.

Here’s how you can use it:

ls /dev/tty*

This command lists all files that start with tty in the /dev directory. The output will show you all potential serial ports. Let's break down what you might see:

• ttyS[number]: These are the traditional serial ports. ttyS0 is usually the first serial port, ttyS1 is the second, and so on. These ports are often associated with physical serial ports on the motherboard.
• ttyUSB[number]: These represent USB serial ports. When you connect a USB device that emulates a serial port (like many Arduino boards), it will appear as ttyUSB0, ttyUSB1, etc.
• ttyACM[number]: These are USB CDC (Communication Device Class) serial ports. Devices like modems or some embedded systems might use this type of serial connection.

Interpreting the Output

Just because a port appears in the list doesn't necessarily mean it's active or connected to a device. It simply means the device file exists. To confirm whether a port is active, you might need to try connecting to it or use other tools to monitor its status. However, this command is a great starting point for identifying potential COM ports.

Example

If you run ls /dev/tty* and see the following output:

/dev/ttyS0  /dev/ttyS1  /dev/ttyUSB0

It means you have two traditional serial ports (ttyS0 and ttyS1) and one USB serial port (ttyUSB0) available on your system.

Method 2: Using dmesg | grep tty

The dmesg command displays the kernel ring buffer, which contains boot-time messages and other system events. When a serial device is connected, the kernel usually logs information about it. You can use dmesg along with grep to filter for relevant entries.

Here’s the command:

dmesg | grep tty

This command pipes the output of dmesg to grep, which filters for lines containing the string tty. The output will show you messages related to serial ports, including when they were detected and any associated information.

Understanding the Output

The output from this command can give you more details about the serial ports. For example, you might see messages indicating the type of device connected, the baud rate, and other configuration details.

Example:

[    0.582342] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[    2.398765] usb 1-1: pl2303 converter now attached to ttyUSB0

In this example, the first line indicates that the serial driver is initialized. The second line shows that a PL2303 USB-to-serial converter has been attached to ttyUSB0. This is a clear indication that ttyUSB0 is an active and connected serial port.

Benefits of Using dmesg

• Detailed Information: Provides more information than just listing the device files.
• Connection History: Shows when devices were connected or disconnected.
• Troubleshooting: Helps identify issues with serial port detection or configuration.

Method 3: Using setserial -g /dev/ttyS*

The setserial command is used to configure and display information about serial ports. The -g option tells setserial to display the port's configuration without modifying it.

Here’s the command:

setserial -g /dev/ttyS*

This command queries the configuration of all ttyS ports. The output will show you whether each port is configured and active. If a port is not configured, setserial will indicate that it cannot access the device.

Interpreting the Output

For each configured serial port, setserial will display information such as the UART type, the port address, and the IRQ number. If a port is not active or not configured, you'll see an error message.

Example:

/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: unknown, Port: 0x02f8, IRQ: 3
/dev/ttyS2: Device or resource busy
/dev/ttyS3: Device or resource busy

In this example, ttyS0 is configured with a 16550A UART, and ttyS1 has an unknown UART type. The messages for ttyS2 and ttyS3 indicate that these ports are either in use or not properly configured.

Notes on setserial

• Root Privileges: You might need root privileges (using sudo) to run setserial.
• Traditional Ports: This command is primarily useful for traditional serial ports (ttyS*). It may not provide much information about USB serial ports (ttyUSB* or ttyACM*).

Method 4: Using udevadm info

The udevadm command is a powerful tool for querying the udev device manager, which handles device events in Linux. You can use it to get detailed information about specific serial ports.

First, identify the device path. For example, if you want to check ttyUSB0, the path is /dev/ttyUSB0. Then, run the following command:

udevadm info --query all --name /dev/ttyUSB0

Replace /dev/ttyUSB0 with the actual path of the serial port you want to check.

Understanding the Output

The output from udevadm info is quite verbose, but it contains a wealth of information about the device. Look for attributes like ID_VENDOR, ID_MODEL, ID_SERIAL, and DRIVER. These attributes can tell you the vendor, model, serial number, and driver associated with the serial port.

Example:

P: /devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0/tty/ttyUSB0
N: ttyUSB0
S: serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Controller_D-if00-port0
S: serial/by-path/pci-0000:00:14.0-usb-0:1:1.0-port0
E: DEVLINKS=/dev/ttyUSB0 /dev/serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Controller_D-if00-port0 /dev/serial/by-path/pci-0000:00:14.0-usb-0:1:1.0-port0
E: DEVNAME=/dev/ttyUSB0
E: DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0/tty/ttyUSB0
E: ID_BUS=usb
E: ID_MODEL=USB-Serial_Controller_D
E: ID_MODEL_ENC=USB-Serial Controller D
E: ID_MODEL_ID=2303
E: ID_REVISION=0300
E: ID_SERIAL=Prolific_Technology_Inc._USB-Serial_Controller_D
E: ID_SERIAL_SHORT=USB-Serial_Controller_D
E: ID_TYPE=port
E: ID_VENDOR=Prolific_Technology_Inc.
E: ID_VENDOR_ENC=Prolific Technology Inc.
E: ID_VENDOR_ID=067b
E: MAJOR=188
E: MINOR=0
E: SUBSYSTEM=tty
E: TAGS=:systemd:
E: USEC_INITIALIZED=1234567

This output shows that ttyUSB0 is a USB serial port connected to a Prolific Technology Inc. USB-Serial Controller. The ID_VENDOR and ID_MODEL attributes provide specific details about the device.

Benefits of Using udevadm info

• Detailed Device Information: Provides comprehensive details about the serial port and its associated device.
• Device Identification: Helps identify the vendor and model of the connected device.
• Troubleshooting: Useful for diagnosing driver issues or device recognition problems.

Method 5: Using GUI Tools (for Desktop Environments)

If you're using a desktop environment like GNOME or KDE, there are GUI tools that can help you identify available COM ports. These tools often provide a more user-friendly interface compared to command-line methods.

Example: Using minicom

minicom is a serial communication program that can help you detect available serial ports. Although it's a terminal-based application, it provides a menu-driven interface that can be easier to navigate than raw command-line tools.

1. Install minicom:

   If you don't have it already, install minicom using your distribution's package manager. For example, on Debian/Ubuntu:

   sudo apt-get install minicom
   

   On Fedora/CentOS:

   sudo yum install minicom
   

2. Run minicom -s:

   This command starts minicom in setup mode.

   minicom -s
   

3. Configure Serial Port:

   In the setup menu, select "Serial port setup".

   You can then cycle through the available serial ports (e.g., /dev/ttyS0, /dev/ttyUSB0, etc.) to see if minicom can open a connection. If a port is available, minicom will usually display a status message indicating that it's ready. If a port is not available, you'll see an error message.

Benefits of Using GUI Tools

• User-Friendly Interface: Easier to navigate for those less comfortable with the command line.
• Visual Feedback: Provides immediate feedback on whether a port is available.
• Configuration Options: Allows you to configure serial port settings directly.

Conclusion

So there you have it, folks! Several ways to check available COM ports in Linux. Whether you prefer the simplicity of ls /dev/tty*, the detailed information from dmesg or udevadm, the configuration options of setserial, or the user-friendly interface of GUI tools like minicom, you now have the knowledge to tackle those serial port mysteries. Happy connecting!