pmdajson(1) — Linux manual page


PMDAJSON(1)                General Commands Manual               PMDAJSON(1)

NAME         top

       pmdajson - JSON PMDA

DESCRIPTION         top

       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 .


       pmdajson reads a mandatory JSON configuration file

           · $PCP_PMDAS_DIR/json/config.json

       This file can contain the following PMDA options using the JSON

           · 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         top

       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         top

       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) and should never be executed
       directly.  The Install and Remove scripts notify pmcd(1) when the
       agent is installed or removed.

FILES         top

              additional documentation for pmdajson used JSON files

              configuration file for the pmdajson agent

              installation script for the pmdajson agent

              undo installation script for the pmdajson agent

              default log file for messages from the pmdajson agent


       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).

SEE ALSO         top

       PCPIntro(1), pmcd(1) and pminfo(1).

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
       Information about the project can be found at ⟨⟩.
       If you have a bug report for this manual page, send it to  This page was obtained from the project's upstream
       Git repository ⟨⟩ on
       2020-08-13.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-08-11.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

Performance Co-Pilot                 PCP                         PMDAJSON(1)