netdata/collectors/charts.d.plugin

charts.d.plugin

charts.d.plugin is a Netdata external plugin. It is an orchestrator for data collection modules written in BASH v4+.

1. It runs as an independent process ps fax shows it
2. It is started and stopped automatically by Netdata
3. It communicates with Netdata via a unidirectional pipe (sending data to the netdata daemon)
4. Supports any number of data collection modules

To better understand the guidelines and the API behind our External plugins, please have a look at the Introduction to External plugins prior to reading this page.

charts.d.plugin has been designed so that the actual script that will do data collection will be permanently in memory, collecting data with as little overheads as possible (i.e. initialize once, repeatedly collect values with minimal overhead).

charts.d.plugin looks for scripts in /usr/lib/netdata/charts.d. The scripts should have the filename suffix: .chart.sh.

Configuration

charts.d.plugin itself can be configured using the configuration file /etc/netdata/charts.d.conf. This file is also a BASH script.

In this file, you can place statements like this:

enable_all_charts="yes"
X="yes"
Y="no"

where X and Y are the names of individual charts.d collector scripts. When set to yes, charts.d will evaluate the collector script (see below). When set to no, charts.d will ignore the collector script.

The variable enable_all_charts sets the default enable/disable state for all charts.

A charts.d module

A charts.d.plugin module is a BASH script defining a few functions.

For a module called X, the following criteria must be met:

1. The module script must be called X.chart.sh and placed in /usr/libexec/netdata/charts.d.

2. If the module needs a configuration, it should be called X.conf and placed in /etc/netdata/charts.d.
   The configuration file X.conf is also a BASH script itself.
   You can edit the default files supplied by Netdata, by editing /etc/netdata/edit-config charts.d/X.conf, where X is the name of the module.

3. All functions and global variables defined in the script and its configuration, must begin with X_.

4. The following functions must be defined:

   • X_check() - returns 0 or 1 depending on whether the module is able to run or not (following the standard Linux command line return codes: 0 = OK, the collector can operate and 1 = FAILED, the collector cannot be used).

   • X_create() - creates the Netdata charts (commands CHART and DIMENSION). The return value does matter: 0 = OK, 1 = FAILED.

   • X_update() - collects the values for the defined charts (commands BEGIN, SET, END). The return value also matters: 0 = OK, 1 = FAILED.

5. The following global variables are available to be set:

   • X_update_every - is the data collection frequency for the module script, in seconds.

The module script may use more functions or variables. But all of them must begin with X_.

X_check()

The purpose of the BASH function X_check() is to check if the module can collect data (or check its config).

For example, if the module is about monitoring a local mysql database, the X_check() function may attempt to connect to a local mysql database to find out if it can read the values it needs.

X_check() is run only once for the lifetime of the module.

X_create()

The purpose of the BASH function X_create() is to create the charts and dimensions using the standard Netdata plugin guidelines.

X_create() will be called just once and only after X_check() was successful. You can however call it yourself when there is need for it (for example to add a new dimension to an existing chart).

A non-zero return value will disable the collector.

X_update()

X_update() will be called repeatedly every X_update_every seconds, to collect new values and send them to Netdata, following the Netdata plugin guidelines.

The function will be called with one parameter: microseconds since the last time it was run. This value should be appended to the BEGIN statement of every chart updated by the collector script.

A non-zero return value will disable the collector.

Useful functions charts.d provides

Module scripts can use the following charts.d functions:

require_cmd command

require_cmd() will check if a command is available in the running system.

For example, your X_check() function may use it like this:

mysql_check() {
    require_cmd mysql || return 1
    return 0
}

Using the above, if the command mysql is not available in the system, the mysql module will be disabled.

fixid "string"

fixid() will get a string and return a properly formatted id for a chart or dimension.

This is an expensive function that should not be used in X_update(). You can keep the generated id in a BASH associative array to have the values availables in X_update(), like this:

declare -A X_ids=()
X_create() {
   local name="a very bad name for id"

   X_ids[$name]="$(fixid "$name")"
}

X_update() {
   local microseconds="$1"

   ...
   local name="a very bad name for id"
   ...

   echo "BEGIN ${X_ids[$name]} $microseconds"
   ...
}

Debugging your collectors

You can run charts.d.plugin by hand with something like this:

# become user netdata
sudo su -s /bin/sh netdata

# run the plugin in debug mode
/usr/libexec/netdata/plugins.d/charts.d.plugin debug 1 X Y Z

Charts.d will run in debug mode, with an update frequency of 1, evaluating only the collector scripts X, Y and Z. You can define zero or more module scripts. If none is defined, charts.d will evaluate all module scripts available.

Keep in mind that if your configs are not in /etc/netdata, you should do the following before running charts.d.plugin:

export NETDATA_USER_CONFIG_DIR="/path/to/etc/netdata"

Also, remember that Netdata runs chart.d.plugin as user netdata (or any other user the netdata process is configured to run as).

Running multiple instances of charts.d.plugin

charts.d.plugin will call the X_update() function one after another. This means that a delay in collector X will also delay the collection of Y and Z.

You can have multiple charts.d.plugin running to overcome this problem.

This is what you need to do:

1. Decide a new name for the new charts.d instance: example charts2.d.

2. Create/edit the files /etc/netdata/charts.d.conf and /etc/netdata/charts2.d.conf and enable / disable the module you want each to run. Remember to set enable_all_charts="no" to both of them, and enable the individual modules for each.

3. link /usr/libexec/netdata/plugins.d/charts.d.plugin to /usr/libexec/netdata/plugins.d/charts2.d.plugin. Netdata will spawn a new charts.d process.

Execute the above in this order, since Netdata will (by default) attempt to start new plugins soon after they are created in /usr/libexec/netdata/plugins.d/.