---
name: "pmdajson"
section: "1"
platform: "linux"
package: "pcp"
version: "6.3.8-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/pmdajson"
---

# pmdajson(1)

JSON PMDA

## NAME

**pmdajson** - JSON PMDA

## DESCRIPTION

**pmdajson** is a Performance Metrics Domain Agent (PMDA) which exports metrics from arbitrary sources generating JavaScript Object Notation (JSON) syntax.

At least one pair of JSON inputs are required for **pmdajson** to provide metrics for PCP clients; one describing metric metadata and one containing metric values data. Metadata is read once from a file at PMDA startup while the data is read every time a request for metric values is made by a PCP client. The data is read either from a JSON file or an external command generating JSON output. More than one pair of JSON inputs can be used to support arbitrary number of metric sources in different configured directories.

The overall JSON format description is at **http://www.json.org/**.

## JSON DATA SOURCES

**pmdajson** reads a mandatory JSON configuration file

-

  - •

    *`$PCP_PMDAS_DIR`/json/config.json*

This file can contain the following PMDA options using the JSON syntax:

-

  - •

    directory\_list

  - •

    trusted\_directory\_list

**pmdajson** searches the directories listed for these options looking for files named *metadata.json* and (by default) *data.json*. The JSON metadata files describe the metric names, types, and other details of the associated JSON metric data. The JSON data file name is configurable, and can also be an external command instead of a periodically updated (by external tools) data file.

Each of these found JSON file/command pairs form a *JSON data source*.

For example, let us assume the following simple JSON data file that contains values for two metrics, one of type string and one numeric:

```
  {
    "string_value": "testing, 1, 2, 3",
    "read_count": 0
  }
```

For these metrics the metadata file needed by **pmdajson** would be:

```
  {
    "metrics": [
      {
        "name": "string_value",
        "pointer": "/string_value",
        "type": "string"
      },
      {
        "name": "read_count",
        "pointer": "/read_count",
        "type": "integer",
        "description": "Times values read"
      }
    ]
  }
```

For further details on the JSON metadata format and options, see the README file included as part of **pmdajson** installation.

## SECURITY MODEL

JSON data sources listed for the *directory\_list* option are not trusted, meaning that if external commands to generate the needed JSON data are used, these commands are run as user **nobody**.

JSON data sources listed for the *trusted\_directory\_list* option are trusted, meaning that if external commands to generate the needed JSON data are used, these commands are run as user **root**.

For further details on security and description on running external commands, see the README file included as part of **pmdajson** installation.

## INSTALLATION

Install the JSON PMDA by using the Install script as root:

```
# cd $PCP_PMDAS_DIR/json
# ./Install
```

To uninstall, do the following as root:

```
# cd $PCP_PMDAS_DIR/json
# ./Remove
```

**pmdajson** is launched by [**pmcd**(1)](/pmcd/1.md) and should never be executed directly. The Install and Remove scripts notify [**pmcd**(1)](/pmcd/1.md) when the agent is installed or removed.

## FILES

- *`$PCP_PMDAS_DIR`/json/README*

  additional documentation for **pmdajson** used JSON files

- *`$PCP_PMDAS_DIR`/json/config.json*

  configuration file for the **pmdajson** agent

- *`$PCP_PMDAS_DIR`/json/Install*

  installation script for the **pmdajson** agent

- *`$PCP_PMDAS_DIR`/json/Remove*

  undo installation script for the **pmdajson** agent

- *`$PCP_LOG_DIR`/pmcd/json.log*

  default log file for messages from the **pmdajson** agent

## PCP ENVIRONMENT

Environment variables with the prefix **PCP\_** are used to parameterize the file and directory names used by PCP. On each installation, the file */etc/pcp.conf* contains the local values for these variables. The **$PCP\_CONF** variable may be used to specify an alternative configuration file, as described in [**pcp.conf**(5)](/pcp.conf/5.md).

## SEE ALSO

[**PCPIntro**(1)](/PCPIntro/1.md), [**pmcd**(1)](/pmcd/1.md) and [**pminfo**(1)](/pminfo/1.md).