setserial Command in Linux

Introduction to Linux Serial Port Configuration with setserial

In this lab, we'll delve into the Linux setserial command and its practical uses for system administration. This tutorial will guide you on how to determine serial port information, adjust serial port settings, and resolve common serial communication problems within a Linux environment. We'll begin with an overview of the setserial command's functionality, proceed to utilizing it for comprehensive serial port data retrieval, and finally, demonstrate the configuration of diverse serial port settings, including baud rate and interrupt request (IRQ), using the setserial command.

Understanding the Functionality of the setserial Command

In this section, we'll examine the purpose of the setserial command within the Linux operating system. The setserial command serves as a robust tool for system administrators to configure and maintain serial port settings on a Linux system.

The setserial command enables you to:

  • Determine the existing configuration of serial ports
  • Modify various parameters for serial ports, such as baud rate, I/O address, and interrupt request (IRQ)
  • Address and fix issues related to serial communication

To begin, let's employ the setserial command to gather information about the serial ports present on your system.

sudo setserial -g /dev/ttyS*

Example output:

/dev/ttyS0 uart:16550A port:0x03f8 irq:4
/dev/ttyS1 uart:16550A port:0x02f8 irq:3

This command fetches the current setup of all serial ports (/dev/ttyS*) on the system. The output presents the UART type, I/O port address, and IRQ for each serial port.

Now, suppose you need to alter the configuration of a specific serial port, such as adjusting the baud rate. You can leverage the setserial command for this purpose:

sudo setserial /dev/ttyS0 baud_base 115200 spd_cust

This command configures the baud rate of the /dev/ttyS0 serial port to 115200 bps and activates custom baud rate settings.

The setserial command offers a broad spectrum of options to fine-tune various aspects of serial ports, including:

  • spd_normal: Set standard baud rates
  • spd_cust: Enable custom baud rates
  • spd_vhi: Set the baud rate to 57600 bps
  • spd_hi: Set the baud rate to 38400 bps
  • spd_shi: Set the baud rate to 115200 bps

You can access the complete list of options by executing man setserial in the terminal.

Identifying Serial Port Details Using setserial

In this section, we'll discover how to use the setserial command to extract detailed information regarding the serial ports on your Linux system, a crucial task for any systemadmin.

Firstly, let's list all the serial ports available on the system:

sudo setserial -g /dev/ttyS*

Example output:

/dev/ttyS0 uart:16550A port:0x03f8 irq:4
/dev/ttyS1 uart:16550A port:0x02f8 irq:3

This command provides the following information for each serial port:

  • uart: The UART (Universal Asynchronous Receiver-Transmitter) type, indicating the serial port hardware.
  • port: The I/O port address of the serial port.
  • irq: The interrupt request (IRQ) number assigned to the serial port.

To retrieve more in-depth information about a specific serial port, you can use the setserial command with the port name as an argument:

sudo setserial /dev/ttyS0 -a

Example output:

/dev/ttyS0, Line 0:
        Baud_base: 115200, close_delay: 50, divisor: 0
        closing_wait: 3000, custom_divisor: 0, max_baud: 0
        port: 0x03f8, irq: 4
        flags: (0x10) UPF_SKIP_TEST
        spd_cust: 0, spd: (0x00)

This command furnishes supplementary details about the /dev/ttyS0 serial port, including the baud rate, close delay, divisor, closing wait, custom divisor, maximum baud rate, and various flags.

Understanding serial port information is essential when configuring or diagnosing serial communication problems on your Linux system.

Configuring Serial Port Attributes with setserial

In this segment, we'll learn how to leverage the setserial command to modify various attributes for the serial ports on your Linux system.

Let's initiate by identifying the serial ports on your system:

sudo setserial -g /dev/ttyS*

Example output:

/dev/ttyS0 uart:16550A port:0x03f8 irq:4
/dev/ttyS1 uart:16550A port:0x02f8 irq:3

Now, let's assume you wish to change the baud rate of the /dev/ttyS0 serial port to 115200 bps and enable custom baud rate settings:

sudo setserial /dev/ttyS0 baud_base 115200 spd_cust

To confirm the modifications, you can execute the setserial command again with the -a option:

sudo setserial /dev/ttyS0 -a

Example output:

/dev/ttyS0, Line 0:
        Baud_base: 115200, close_delay: 50, divisor: 0
        closing_wait: 3000, custom_divisor: 0, max_baud: 0
        port: 0x03f8, irq: 4
        flags: (0x10) UPF_SKIP_TEST
        spd_cust: 1, spd: (0x00)

The output demonstrates that the baud rate is now set to 115200 bps, and the spd_cust flag is enabled, granting you the ability to utilize custom baud rates.

You can also employ the setserial command to configure other serial port attributes, such as:

  • spd_normal: Set the standard baud rates
  • spd_vhi: Set the baud rate to 57600 bps
  • spd_hi: Set the baud rate to 38400 bps
  • spd_shi: Set the baud rate to 115200 bps
  • uart: Set the UART type (e.g., uart:16550A)
  • port: Set the I/O port address
  • irq: Set the interrupt request (IRQ) number

Remember to consult the man setserial page for a comprehensive list of available options and their descriptions, crucial for effective systemadmin tasks.

Conclusion

In this lab, we gained insight into the functionality and application of the setserial command in Linux. We commenced by understanding how the setserial command can be employed to identify the existing configuration of serial ports, encompassing the UART type, I/O port address, and IRQ. We subsequently explored how to utilize the setserial command to configure various settings for serial ports, such as baud rate and custom baud rates. Finally, we learned how to leverage the setserial command to acquire detailed information about the serial ports on the system, including their device names, UART types, and other relevant details, making us more proficient Linux systemadmins.

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