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Memory metrics

{% hint style="info" %} Supported event types: logs {% endhint %}

The Memory (mem) input plugin gathers memory and swap usage on Linux at a fixed interval and reports totals and free space. The plugin emits log-based metrics (for Prometheus-format metrics see the Node Exporter metrics input plugin).

Metrics reported

Key Description Units
Mem.free Free or available memory reported by the kernel. Kilobytes
Mem.total Total system memory. Kilobytes
Mem.used Memory in use (Mem.total - Mem.free). Kilobytes
proc_bytes Optional. Resident set size for the configured process (pid). Bytes
proc_hr Optional. Human-readable value of proc_bytes (for example, 12.00M). Formatted
Swap.free Free swap space. Kilobytes
Swap.total Total system swap. Kilobytes
Swap.used Swap space in use (Swap.total - Swap.free). Kilobytes

Configuration parameters

The plugin supports the following configuration parameters:

Key Description Default
interval_nsec Polling interval in nanoseconds. 0
interval_sec Polling interval in seconds. 1
pid Process ID to measure. When set, the plugin also reports proc_bytes and proc_hr. none
threaded Run this input in its own thread. false

Get started

To collect memory and swap usage from your system, run the plugin from the command line or through the configuration file.

Command line

Run the following command from the command line:

fluent-bit -i mem -t memory -o stdout -m '*'

The output is similar to:

...
[0] memory: [[1751381087.225589224, {}], {"Mem.total"=>3986708, "Mem.used"=>560708, "Mem.free"=>3426000, "Swap.total"=>0, "Swap.used"=>0, "Swap.free"=>0}]
[0] memory: [[1751381088.228411537, {}], {"Mem.total"=>3986708, "Mem.used"=>560708, "Mem.free"=>3426000, "Swap.total"=>0, "Swap.used"=>0, "Swap.free"=>0}]
[0] memory: [[1751381089.225600084, {}], {"Mem.total"=>3986708, "Mem.used"=>561480, "Mem.free"=>3425228, "Swap.total"=>0, "Swap.used"=>0, "Swap.free"=>0}]
[0] memory: [[1751381090.228345064, {}], {"Mem.total"=>3986708, "Mem.used"=>561480, "Mem.free"=>3425228, "Swap.total"=>0, "Swap.used"=>0, "Swap.free"=>0}]
...

Configuration file

In your main configuration file append the following:

{% tabs %} {% tab title="fluent-bit.yaml" %}

pipeline:
  inputs:
    - name: mem
      tag: memory
      interval_sec: 5
      pid: 1234

  outputs:
    - name: stdout
      match: '*'

{% endtab %} {% tab title="fluent-bit.conf" %}

[INPUT]
  Name          mem
  Tag           memory
  Interval_Sec  5
  Interval_Nsec 0
  Pid           1234

[OUTPUT]
  Name   stdout
  Match  *

{% endtab %} {% endtabs %}

Example output when pid is set:

...
[0] memory: [[1751381087.225589224, {}], {"Mem.total"=>3986708, "Mem.used"=>560708, "Mem.free"=>3426000, "Swap.total"=>0, "Swap.used"=>0, "Swap.free"=>0, "proc_bytes"=>12349440, "proc_hr"=>"11.78M"}]
...