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.

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.

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

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

  1. [INPUT]
  2.     Name           head
  3.     Tag            head.cpu
  4.     File           /proc/cpuinfo
  5.     Lines          8
  6.     Split_line     true
  7.     # {"line0":"processor    : 0", "line1":"vendor_id    : GenuineIntel" ...}
  9. [FILTER]
  10.     Name           record_modifier
  11.     Match          *
  12.     Whitelist_key  line7
  14. [OUTPUT]
  15.     Name           stdout
  16.     Match          *

Output is

  1. $ bin/fluent-bit -c head.conf 
  2. Fluent-Bit v0.12.0
  3. Copyright (C) Treasure Data
  5. [2017/06/26 22:38:24] [ info] [engine] started
  6. [0] head.cpu: [1498484305.000279805, {"line7"=>"cpu MHz        : 2791.009"}]
  7. [1] head.cpu: [1498484306.011680137, {"line7"=>"cpu MHz        : 2791.009"}]
  8. [2] head.cpu: [1498484307.010042482, {"line7"=>"cpu MHz        : 2791.009"}]
  9. [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:

  1. $ fluent-bit -i head -t uptime -p File=/proc/uptime -o stdout -m '*'
  2. Fluent-Bit v0.8.0
  3. Copyright (C) Treasure Data
  5. [2016/05/17 21:53:54] [ info] starting engine
  6. [0] uptime: [1463543634, {"head"=>"133517.70 194870.97"}]
  7. [1] uptime: [1463543635, {"head"=>"133518.70 194872.85"}]
  8. [2] uptime: [1463543636, {"head"=>"133519.70 194876.63"}]
  9. [3] uptime: [1463543637, {"head"=>"133520.70 194879.72"}]

Configuration File

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

  1. [INPUT]
  2.     Name          head
  3.     Tag           uptime
  4.     File          /proc/uptime
  5.     Buf_Size      256
  6.     Interval_Sec  1
  7.     Interval_NSec 0
  9. [OUTPUT]
  10.     Name   stdout
  11.     Match  *

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

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