# 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](https://docs.fluentbit.io/manual/administration/multithreading#inputs). | `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:

```shell
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" %}

```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"}]
...
```