setserial

Print all information about a serial device

$ setserial -a [/dev/ttyS0]

$ setserial -b [/dev/ttyS0]

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

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

$ sudo setserial [/dev/ttyS0] autoconfig

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

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.

-a

Display all available configuration information

Print summary configuration suitable for bootup scripts

Report characteristics of multiple devices

Print configuration as setserial command-line arguments

Quiet mode; suppress status output

Verbose mode; display additional status info

Print version and exit

Zero out flags before setting new values

Set the I/O port address

Set the interrupt request line

Set UART type (none, 8250, 16450, 16550, 16550A, 16650, 16750, etc.)

Automatically detect UART type and IRQ

Set base baud rate (clock frequency / 16)

Set custom clock divisor for non-standard baud rates

Minimize receive latency at the cost of CPU overhead

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 The -W wild interrupt initialization is obsolete on modern kernels.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

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.

stty(1), getty(8), minicom(1), cu(1)