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