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eschabell merged 1 commit into from
Dec 5, 2025
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pipeline: inputs: memory-metrics: update doc with metrics table, examples, and pid output #2281

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56 changes: 44 additions & 12 deletions pipeline/inputs/memory-metrics.md
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Original file line number Diff line number Diff line change
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# Memory metrics

The _Memory_ (`mem`) input plugin gathers information about the memory and swap usage of the running system every certain interval of time and reports the total amount of memory and the amount of free available.
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](../../administration/multithreading.md#inputs). | `false` |

## Get started

To get memory and swap usage from your system, you can run the plugin from the command line or through the configuration file:
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, noting this is for a Linux machine:
Run the following command from the command line:

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

Which outputs information similar to:
The output is similar to:

```text
...
Expand All @@ -25,11 +49,6 @@ Which outputs information similar to:
...
```

## Threading

You can enable the `threaded` setting to run this input in its own
[thread](../../administration/multithreading.md#inputs).

### Configuration file

In your main configuration file append the following:
Expand All @@ -42,6 +61,8 @@ pipeline:
inputs:
- name: mem
tag: memory
interval_sec: 5
pid: 1234

outputs:
- name: stdout
Expand All @@ -53,13 +74,24 @@ pipeline:

```text
[INPUT]
Name mem
Tag memory
Name mem
Tag memory
Interval_Sec 5
Interval_NSec 0
PID 1234

[OUTPUT]
Name stdout
Match *
```

{% endtab %}
{% endtabs %}
{% endtabs %}

Example output when `pid` is set:

```text
...
[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"}]
...
```