Memory metrics

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
Swap.free	Free swap space.	Kilobytes
Swap.total	Total system swap.	Kilobytes
Swap.used	Swap space in use (Swap.total - Swap.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

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:

fluent-bit.yaml

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

  outputs:
    - name: stdout
      match: '*'

fluent-bit.conf

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"}]
...