pmdajson is a Performance Metrics Domain Agent (PMDA) which
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
The overall JSON format description is at http://www.json.org/.
pmdajson reads a mandatory JSON configuration file
This file can contain the following PMDA options using the JSON
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 datasource.
For example, let us assume the following simple JSON data file
that contains values for two metrics, one of type string and one
"string_value": "testing, 1, 2, 3",
For these metrics the metadata file needed by pmdajson would be:
"description": "Times values read"
For further details on the JSON metadata format and options, see
the README file included as part of pmdajson installation.
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
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# ./Removepmdajson 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.
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
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at
⟨http://www.pcp.io/⟩. If you have a bug report for this manual
page, send it to firstname.lastname@example.org. This page was obtained from the
project's upstream Git repository
⟨https://github.com/performancecopilot/pcp.git⟩ on 2020-12-18.
(At that time, the date of the most recent commit that was found
in the repository was 2020-12-18.) 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)