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+# 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](https://github.com/netdata/netdata/blob/master/collectors/plugins.d/README.md) 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`.
+
+By default, `charts.d.plugin` is not included as part of the install when using [our official native DEB/RPM packages](https://github.com/netdata/netdata/blob/master/packaging/installer/methods/packages.md). You can install it by installing the `netdata-plugin-chartsd` package.
+
+## Configuration
+
+`charts.d.plugin` itself can be [configured](https://github.com/netdata/netdata/blob/master/docs/configure/nodes.md#use-edit-config-to-edit-configuration-files) 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:
+
+```conf
+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:
+
+```sh
+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:
+
+```sh
+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:
+
+```sh
+# 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`:
+
+```sh
+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/`.