Ever wondered how to peek under the hood of your Linux system and see which COM ports are up for grabs? Whether you're connecting serial devices, debugging hardware, or just curious about your system's configuration, knowing how to check available COM ports is a handy skill. This guide will walk you through the process step-by-step, ensuring you can confidently identify and utilize those ports.

Why Check COM Ports?

Before we dive into the how-to, let's quickly cover why you might need to do this. COM ports, short for communication ports, are essential interfaces for connecting various serial devices to your computer. These devices can range from legacy hardware like modems and printers to modern equipment like microcontrollers, sensors, and embedded systems. When working with these devices, you need to know which COM ports are available and their corresponding device names in Linux (typically something like /dev/ttyS0 or /dev/ttyUSB0).

• Device Connectivity: Identifying the correct COM port is crucial for establishing communication with your serial devices. Without knowing the right port, your software won't be able to send or receive data, rendering your device useless.
• Troubleshooting: If you're experiencing issues with a serial device, checking the COM ports can help you pinpoint the problem. For instance, if a device isn't responding, it might be connected to the wrong port, or the port might not be enabled.
• Configuration: Some applications require you to manually specify the COM port to use. Knowing the available ports allows you to configure the application correctly.
• Hardware Detection: Checking COM ports can also help you verify that your system has correctly detected and enumerated your serial devices. This is particularly useful when adding new hardware or troubleshooting driver issues.

In essence, checking COM ports is a fundamental step in working with serial devices on Linux. It ensures that you can connect, communicate, and troubleshoot effectively.

Methods to Check Available COM Ports

Alright, let's get down to the nitty-gritty. Here are several methods you can use to check available COM ports in Linux, ranging from simple command-line tools to more advanced techniques. We'll start with the easiest and most common methods.

1. Using ls /dev/tty*

The simplest way to get a quick overview of potential COM ports is by listing the contents of the /dev directory, which is where device files reside in Linux. Specifically, we're looking for files that start with tty (teletypewriter), as these typically represent serial ports. Open your terminal and type:

ls /dev/tty*

This command will display a list of all files in the /dev directory that begin with tty. Here's a breakdown of what you might see:

• /dev/ttyS*: These are the classic serial ports, often associated with physical COM ports on your computer. For example, /dev/ttyS0 usually corresponds to COM1, /dev/ttyS1 to COM2, and so on.
• /dev/ttyUSB*: These represent USB serial ports, which are commonly used by USB-to-serial adapters and devices that emulate serial ports over USB. For example, /dev/ttyUSB0 is often the first USB serial port detected by the system.
• /dev/ttyACM*: These are typically used for USB CDC ACM (USB Communications Device Class Abstract Control Model) devices, such as modems and some embedded systems.
• Other tty devices: You might also see other tty devices, such as /dev/tty, /dev/tty0, and /dev/ttyN (where N is a number). These are usually related to virtual terminals and consoles and are not typically used for serial communication with external devices.

Interpreting the Output:

The output of ls /dev/tty* gives you a list of potential COM ports, but it doesn't tell you whether a device is actually connected to each port. It simply shows you the device files that exist in the system. To determine if a device is connected, you'll need to use other methods, such as checking for activity on the port or using a serial communication program to test the connection.

Example:

If the output of ls /dev/tty* includes /dev/ttyS0 and /dev/ttyUSB0, it means that your system has detected a classic serial port (COM1) and a USB serial port. You can then try connecting your serial device to either of these ports and see if it works.

2. Using dmesg | grep tty

The dmesg command displays the kernel's ring buffer, which contains messages related to hardware detection, driver loading, and other system events. By filtering the output of dmesg with grep tty, you can see messages specifically related to serial ports. This can provide more information about the detected COM ports and the devices connected to them. Open your terminal and type:

dmesg | grep tty

This command will display a list of kernel messages that contain the word "tty". Look for messages that indicate the detection of serial ports, such as:

• [ 0.000000] console [tty0] enabled: This message indicates that the system console is enabled on tty0.
• [ 1.234567] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A: This message indicates that a classic serial port (ttyS0) has been detected at a specific I/O address and IRQ.
• [ 10.987654] usb 1-2: cp210x converter now attached to ttyUSB0: This message indicates that a USB-to-serial converter (in this case, a CP210x) has been detected and attached to ttyUSB0.

Interpreting the Output:

The output of dmesg | grep tty provides more detailed information about the detected serial ports than ls /dev/tty*. It can tell you the type of serial port (e.g., classic serial port, USB-to-serial converter), the I/O address and IRQ (for classic serial ports), and the specific driver used for the device. This information can be helpful for troubleshooting driver issues or configuring your serial device.

Example:

If the output of dmesg | grep tty includes the message usb 1-2: cp210x converter now attached to ttyUSB0, it means that a CP210x USB-to-serial converter has been detected and assigned to ttyUSB0. You can then use ttyUSB0 as the COM port for your serial device.

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 information about the specified serial ports. This method is particularly useful for checking the configuration of classic serial ports (/dev/ttyS*). Open your terminal and type:

setserial -g /dev/ttyS*

This command will display information about each /dev/ttyS* device, including its UART type, I/O address, IRQ, and other configuration parameters. If a serial port is not configured or does not exist, setserial will typically report that it is "not a standard serial port".

Interpreting the Output:

The output of setserial -g /dev/ttyS* provides detailed information about the configuration of classic serial ports. This can be helpful for troubleshooting issues related to serial port configuration, such as incorrect I/O addresses or IRQs. However, setserial is not typically used for USB serial ports (/dev/ttyUSB*) or other types of serial devices.

Example:

If the output of setserial -g /dev/ttyS* includes the following:

/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: unknown, Port: 0x02f8, IRQ: 3

It means that /dev/ttyS0 is configured as a standard serial port with a 16550A UART, I/O address 0x03f8, and IRQ 4. /dev/ttyS1 is also detected, but its UART type is unknown, which might indicate that it is not properly configured or that no device is connected to it.

4. Using udevadm info

The udevadm command is a powerful tool for querying the udev device manager, which is responsible for managing device files in Linux. By using udevadm info, you can retrieve detailed information about specific device files, including their attributes, properties, and relationships to other devices. This method is particularly useful for USB serial ports (/dev/ttyUSB*) and other devices that are managed by udev. To use udevadm info, you need to know the device file you want to query. For example, to get information about /dev/ttyUSB0, you would type:

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

This command will display a large amount of information about /dev/ttyUSB0, including its device attributes, properties, and environment variables. Look for information related to the device's manufacturer, model, serial number, and other identifying characteristics.

Interpreting the Output:

The output of udevadm info can be overwhelming, but it provides a wealth of information about the specified device file. By examining the output, you can learn about the device's capabilities, its relationship to other devices, and any specific configuration settings that have been applied to it. This information can be helpful for troubleshooting device-related issues or customizing the behavior of your system.

Example:

If the output of udevadm info --query all --name /dev/ttyUSB0 includes the following:

  ATTRS{idVendor}=="10c4"
  ATTRS{idProduct}=="ea60"
  ATTRS{serial}=="0001"

It means that /dev/ttyUSB0 is associated with a USB device that has a vendor ID of 10c4, a product ID of ea60, and a serial number of 0001. This information can be used to identify the specific type of USB-to-serial converter that is connected to the system.

Conclusion

Checking available COM ports in Linux is a fundamental skill for anyone working with serial devices. By using the methods outlined in this guide, you can confidently identify and utilize those ports, ensuring that you can connect, communicate, and troubleshoot effectively. From simple command-line tools like ls /dev/tty* and dmesg | grep tty to more advanced techniques like setserial -g /dev/ttyS* and udevadm info, there's a method for every situation. So go ahead, explore your system's COM ports and unlock the power of serial communication!