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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 v4.0.3
* Copyright (C) 2015-2025 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

______ _                  _    ______ _ _             ___  _____
|  ___| |                | |   | ___ (_) |           /   ||  _  |
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   __/ /| || |/' |
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / / /_| ||  /| |
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V /\___  |\ |_/ /
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/     |_(_)___/


[2025/07/01 14:44:47] [ info] [fluent bit] version=4.0.3, commit=f5f5f3c17d, pid=1
[2025/07/01 14:44:47] [ info] [storage] ver=1.5.3, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2025/07/01 14:44:47] [ info] [simd    ] disabled
[2025/07/01 14:44:47] [ info] [cmetrics] version=1.0.3
[2025/07/01 14:44:47] [ info] [ctraces ] version=0.6.6
[2025/07/01 14:44:47] [ info] [input:mem:mem.0] initializing
[2025/07/01 14:44:47] [ info] [input:mem:mem.0] storage_strategy='memory' (memory only)
[2025/07/01 14:44:47] [ info] [sp] stream processor started
[2025/07/01 14:44:47] [ info] [engine] Shutdown Grace Period=5, Shutdown Input Grace Period=2
[2025/07/01 14:44:47] [ info] [output:stdout:stdout.0] worker #0 started
[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 v4.0.3
* Copyright (C) 2015-2025 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

______ _                  _    ______ _ _             ___  _____
|  ___| |                | |   | ___ (_) |           /   ||  _  |
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   __/ /| || |/' |
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / / /_| ||  /| |
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V /\___  |\ |_/ /
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/     |_(_)___/


[2025/07/01 14:44:47] [ info] [fluent bit] version=4.0.3, commit=f5f5f3c17d, pid=1
[2025/07/01 14:44:47] [ info] [storage] ver=1.5.3, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2025/07/01 14:44:47] [ info] [simd    ] disabled
[2025/07/01 14:44:47] [ info] [cmetrics] version=1.0.3
[2025/07/01 14:44:47] [ info] [ctraces ] version=0.6.6
[2025/07/01 14:44:47] [ info] [input:mem:mem.0] initializing
[2025/07/01 14:44:47] [ info] [input:mem:mem.0] storage_strategy='memory' (memory only)
[2025/07/01 14:44:47] [ info] [sp] stream processor started
[2025/07/01 14:44:47] [ info] [engine] Shutdown Grace Period=5, Shutdown Input Grace Period=2
[2025/07/01 14:44:47] [ info] [output:stdout:stdout.0] worker #0 started
[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:

pipeline:
    inputs:
        - name: serial
          tag: data
          file: /dev/tnt0
          bitrate: 9600
          separator: X

    outputs:
        - 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

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