Serial Interface

The Serial input plugin lets you retrieve messages and data from a serial interface.

Configuration parameters

This plugin has the following configuration parameters:

Key	Description	Default
File	Absolute path to the device entry. For example, /dev/ttyS0.	none
Bitrate	The bit rate for the communication. For example: 9600, 38400, 115200.	none
Min_Bytes	The serial interface expects at least Min_Bytes to be available before processing the message.	1
Separator	Specify a separator string that's used to determinate when a message ends.	none
Format	Specify the format of the incoming data stream. Format and Separator can't be used at the same time.	json (no other options available)
Threaded	Indicates whether to run this input in its own thread.	false

Get started

To retrieve messages by using the Serial interface, you can run the plugin from the command line or through the configuration file:

Command line

The following example loads the input serial plugin where it set a Bitrate of 9600, listens from the /dev/tnt0 interface, and uses the custom tag data to route the message.

fluent-bit -i serial -t data -p File=/dev/tnt0 -p BitRate=9600 -o stdout -m '*'

The interface (/dev/tnt0) is an emulation of the serial interface. Further examples will write some message to the other end of the interface. For example, /dev/tnt1.

echo 'this is some message' > /dev/tnt1

In Fluent Bit you can run the command:

fluent-bit -i serial -t data -p File=/dev/tnt0 -p BitRate=9600 -o stdout -m '*'

Which should produce output like:

Fluent Bit v1.x.x
* Copyright (C) 2019-2020 The Fluent Bit Authors
* Copyright (C) 2015-2018 Treasure Data
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2016/05/20 15:44:39] [ info] starting engine
[0] data: [1463780680, {"msg"=>"this is some message"}]

Using the Separator configuration, you can send multiple messages at once.

Run this command after starting Fluent Bit:

echo 'aaXbbXccXddXee' > /dev/tnt1

Then, run Fluent Bit:

fluent-bit -i serial -t data -p File=/dev/tnt0 -p BitRate=9600 -p Separator=X -o stdout -m '*'

This should produce results similar to the following:

Fluent-Bit v0.8.0
Copyright (C) Treasure Data

[2016/05/20 16:04:51] [ info] starting engine
[0] data: [1463781902, {"msg"=>"aa"}]
[1] data: [1463781902, {"msg"=>"bb"}]
[2] data: [1463781902, {"msg"=>"cc"}]
[3] data: [1463781902, {"msg"=>"dd"}]

Configuration file

In your main configuration file append the following sections:

[INPUT]
    Name      serial
    Tag       data
    File      /dev/tnt0
    BitRate   9600
    Separator X

[OUTPUT]
    Name   stdout
    Match  *

Emulating a serial interface on Linux

You can emulate a serial interface on your Linux system and test the serial input plugin locally when you don't have an interface in your computer. The following procedure has been tested on Ubuntu 15.04 running Linux Kernel 4.0.

Build and install the tty0tty module

1. Download the sources:

   git clone https://github.com/freemed/tty0tty

2. Unpack and compile:

   cd tty0tty/module
   make

3. Copy the new kernel module into the kernel modules directory:

   sudo cp tty0tty.ko /lib/modules/$(uname -r)/kernel/drivers/misc/

4. Load the module:

   sudo depmod
   sudo modprobe tty0tty

   You should see new serial ports in dev (ls /dev/tnt\*\).

5. Give appropriate permissions to the new serial ports:

   sudo chmod 666 /dev/tnt*

When the module is loaded, it will interconnect the following virtual interfaces:

/dev/tnt0 <=> /dev/tnt1
/dev/tnt2 <=> /dev/tnt3
/dev/tnt4 <=> /dev/tnt5
/dev/tnt6 <=> /dev/tnt7