setserial

Configure and query serial port settings

TLDR

Print all information about a serial device

$ setserial -a [/dev/ttyS0]

Print configuration summary suitable for bootup

$ setserial -b [/dev/ttyS0]

Set a configuration parameter

$ sudo setserial [/dev/ttyS0] [parameter] [value]

Print configuration of multiple devices

$ setserial -g [/dev/ttyS0] [/dev/ttyS1]

Auto-configure UART type and IRQ

$ sudo setserial [/dev/ttyS0] autoconfig

Set custom baud rate divisor

$ sudo setserial [/dev/ttyS0] baud_base [115200] divisor [1]

SYNOPSIS

setserial [-abqvVWz] device [parameter [arg]]...setserial -g [-abGv] device...

setserial configures and queries serial port settings including I/O port addresses, IRQ lines, UART types, and operational flags. It is primarily used during system startup to initialize serial ports beyond the standard COM1-COM4 ports or to configure non-standard hardware.The command can auto-detect UART types and set custom baud rates for specialized hardware. Modern systems with udev often handle serial configuration automatically, but setserial remains useful for legacy hardware and custom configurations.

PARAMETERS

-a

Display all available configuration information

-b

Print summary configuration suitable for bootup scripts

-g

Report characteristics of multiple devices

-G

Print configuration as setserial command-line arguments

-q

Quiet mode; suppress status output

-v

Verbose mode; display additional status info

-V

Print version and exit

-z

Zero out flags before setting new values

port portnumber_

Set the I/O port address

irq irqnumber_

Set the interrupt request line

uart uarttype_

Set UART type (none, 8250, 16450, 16550, 16550A, 16650, 16650V2, 16654, 16750, 16850, 16950, 16954)

autoconfig

Automatically detect UART type and IRQ

baud_base baud

Set base baud rate (clock frequency / 16)

divisor divisor

Set custom clock divisor for non-standard baud rates

spd_hi

Use 57600 baud when an application requests 38400 baud

spd_vhi

Use 115200 baud when an application requests 38400 baud

spd_cust

Use custom divisor (set via divisor parameter) when an application requests 38400 baud

spd_normal

Use standard 38400 baud rate (resets spdhi, spdvhi, etc.)

close_delay delay

Time in hundredths of a second that DTR should be kept low after port close

closing_wait delay

Time in hundredths of a second to wait for data to drain on close

auto_irq

Attempt to determine IRQ during autoconfig

^auto_irq

Disable automatic IRQ detection during autoconfig

skip_test

Skip UART test during autoconfig

low_latency

Minimize receive latency at the cost of CPU overhead

^low_latency

Disable low latency mode (default)

CAVEATS

Incorrect settings can cause serial ports to malfunction or conflict with other devices. The -W wild interrupt initialization is obsolete on kernels after version 2.1. Many settings require root privileges. On systems using systemd, serial port configuration may be handled differently through udev rules.

HISTORY

setserial was written by Theodore Ts'o and has been part of Linux since the early 1990s, originally to help configure the diverse serial hardware of that era. The tool became essential for setting up modems, terminals, and serial mice. While less critical on modern hardware with automatic detection, it remains in the setserial package for legacy support.