Fluent Bit: Official Manual
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4.0
4.0
  • Fluent Bit v4.0 Documentation
  • About
    • What is Fluent Bit?
    • A Brief History of Fluent Bit
    • Fluentd & Fluent Bit
    • License
    • Sandbox and Lab Resources
  • Concepts
    • Key Concepts
    • Buffering
    • Data Pipeline
      • Input
      • Parser
      • Filter
      • Buffer
      • Router
      • Output
  • Installation
    • Getting Started with Fluent Bit
    • Upgrade Notes
    • Supported Platforms
    • Requirements
    • Sources
      • Download Source Code
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      • Build with Static Configuration
    • Linux Packages
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      • Debian
      • Ubuntu
      • Raspbian / Raspberry Pi
    • Docker
    • Containers on AWS
    • Amazon EC2
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    • macOS
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    • Yocto / Embedded Linux
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  • Administration
    • Configuring Fluent Bit
      • YAML Configuration
        • Service
        • Parsers
        • Multiline Parsers
        • Pipeline
        • Plugins
        • Upstream Servers
        • Environment Variables
        • Includes
      • Classic mode
        • Format and Schema
        • Configuration File
        • Variables
        • Commands
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        • Record Accessor
      • Unit Sizes
      • Multiline Parsing
    • Transport Security
    • Buffering & Storage
    • Backpressure
    • Scheduling and Retries
    • Networking
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    • Monitoring
    • Multithreading
    • HTTP Proxy
    • Hot Reload
    • Troubleshooting
    • Performance Tips
    • AWS credentials
  • Local Testing
    • Validating your Data and Structure
    • Running a Logging Pipeline Locally
  • Data Pipeline
    • Pipeline Monitoring
    • Inputs
      • Collectd
      • CPU Log Based Metrics
      • Disk I/O Log Based Metrics
      • Docker Events
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      • Dummy
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      • Exec Wasi
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      • Forward
      • Head
      • Health
      • HTTP
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      • Kubernetes Events
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      • MQTT
      • Network I/O Log Based Metrics
      • NGINX Exporter Metrics
      • Node Exporter Metrics
      • OpenTelemetry
      • Podman Metrics
      • Process Exporter Metrics
      • Process Log Based Metrics
      • Prometheus Remote Write
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      • Splunk
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      • StatsD
      • Syslog
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      • Windows Event Log
      • Windows Event Log (winevtlog)
      • Windows Exporter Metrics
    • Parsers
      • Configuring Parser
      • JSON
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      • Logfmt
      • Decoders
    • Processors
      • Content Modifier
      • Labels
      • Metrics Selector
      • OpenTelemetry Envelope
      • Sampling
      • SQL
      • Filters as processors
      • Conditional processing
    • Filters
      • AWS Metadata
      • CheckList
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      • Expect
      • GeoIP2 Filter
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      • Kubernetes
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      • Rewrite Tag
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    • Outputs
      • Amazon CloudWatch
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      • Amazon S3
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      • Azure Logs Ingestion API
      • Counter
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      • File
      • FlowCounter
      • Forward
      • GELF
      • Google Chronicle
      • Google Cloud BigQuery
      • HTTP
      • InfluxDB
      • Kafka
      • Kafka REST Proxy
      • LogDNA
      • Loki
      • Microsoft Fabric
      • NATS
      • New Relic
      • NULL
      • Observe
      • OpenObserve
      • OpenSearch
      • OpenTelemetry
      • Oracle Log Analytics
      • PostgreSQL
      • Prometheus Exporter
      • Prometheus Remote Write
      • SkyWalking
      • Slack
      • Splunk
      • Stackdriver
      • Standard Output
      • Syslog
      • TCP & TLS
      • Treasure Data
      • Vivo Exporter
      • WebSocket
  • Stream Processing
    • Introduction to Stream Processing
    • Overview
    • Changelog
    • Getting Started
      • Fluent Bit + SQL
      • Check Keys and NULL values
      • Hands On! 101
  • Fluent Bit for Developers
    • C Library API
    • Ingest Records Manually
    • Golang Output Plugins
    • WASM Filter Plugins
    • WASM Input Plugins
    • Developer guide for beginners on contributing to Fluent Bit
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On this page
  • Configuration Parameters
  • Split Line Mode
  • Getting Started
  • Command Line
  • Configuration File

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  1. Data Pipeline
  2. Inputs

Head

The head input plugin, allows to read events from the head of file. It's behavior is similar to the head command.

Configuration Parameters

The plugin supports the following configuration parameters:

Key
Description

File

Absolute path to the target file, e.g: /proc/uptime

Buf_Size

Buffer size to read the file.

Interval_Sec

Polling interval (seconds).

Interval_NSec

Polling interval (nanosecond).

Add_Path

If enabled, filepath is appended to each records. Default value is false.

Key

Rename a key. Default: head.

Lines

Line number to read. If the number N is set, in_head reads first N lines like head(1) -n.

Split_line

If enabled, in_head generates key-value pair per line.

Threaded

Split Line Mode

This mode is useful to get a specific line. This is an example to get CPU frequency from /proc/cpuinfo.

/proc/cpuinfo is a special file to get cpu information.

processor    : 0
vendor_id    : GenuineIntel
cpu family   : 6
model        : 42
model name   : Intel(R) Core(TM) i7-2640M CPU @ 2.80GHz
stepping     : 7
microcode    : 41
cpu MHz      : 2791.009
cache size   : 4096 KB
physical id  : 0
siblings     : 1

Cpu frequency is "cpu MHz : 2791.009". We can get the line with this configuration file.

[INPUT]
    Name           head
    Tag            head.cpu
    File           /proc/cpuinfo
    Lines          8
    Split_line     true
    # {"line0":"processor    : 0", "line1":"vendor_id    : GenuineIntel" ...}

[FILTER]
    Name           record_modifier
    Match          *
    Whitelist_key  line7

[OUTPUT]
    Name           stdout
    Match          *
pipeline:
    inputs:
        - name: head
          tag: head.cpu
          file: /proc/cpuinfo
          lines: 8
          split_line: true
    filters:
        - name: record_modifier
          match: '*'
          whitelist_key: line7
    outputs:
        - name: stdout
          match: '*'

Output is

$ bin/fluent-bit -c head.conf
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

[2017/06/26 22:38:24] [ info] [engine] started
[0] head.cpu: [1498484305.000279805, {"line7"=>"cpu MHz        : 2791.009"}]
[1] head.cpu: [1498484306.011680137, {"line7"=>"cpu MHz        : 2791.009"}]
[2] head.cpu: [1498484307.010042482, {"line7"=>"cpu MHz        : 2791.009"}]
[3] head.cpu: [1498484308.008447978, {"line7"=>"cpu MHz        : 2791.009"}]

Getting Started

In order to read the head of a file, you can run the plugin from the command line or through the configuration file:

Command Line

The following example will read events from the /proc/uptime file, tag the records with the uptime name and flush them back to the stdout plugin:

$ fluent-bit -i head -t uptime -p File=/proc/uptime -o stdout -m '*'
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

[2016/05/17 21:53:54] [ info] starting engine
[0] uptime: [1463543634, {"head"=>"133517.70 194870.97"}]
[1] uptime: [1463543635, {"head"=>"133518.70 194872.85"}]
[2] uptime: [1463543636, {"head"=>"133519.70 194876.63"}]
[3] uptime: [1463543637, {"head"=>"133520.70 194879.72"}]

Configuration File

In your main configuration file append the following Input & Output sections:

[INPUT]
    Name          head
    Tag           uptime
    File          /proc/uptime
    Buf_Size      256
    Interval_Sec  1
    Interval_NSec 0

[OUTPUT]
    Name   stdout
    Match  *
pipeline:
    inputs:
        - name: head
          tag: uptime
          file: /proc/uptime
          buf_size: 256
          interval_sec: 1
          interval_nsec: 0
    outputs:
        - name: stdout
          match: '*'

Note: Total interval (sec) = Interval_Sec + (Interval_Nsec / 1000000000).

e.g. 1.5s = 1s + 500000000ns

Last updated 1 month ago

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Indicates whether to run this input in its own . Default: false.

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