Project: Netdata (Observability and Analysis / Observability)
File: REFERENCE.md

Netdata's health watchdog is highly configurable, with support for dynamic thresholds, hysteresis, alert templates, and more. You can tweak any of the existing alerts based on your infrastructure's topology or specific monitoring needs, or create new entities. You can use health alerts in conjunction with any of Netdata's (see the ) to monitor the health of your systems, containers, and applications in real time. While you can see active alerts both on the local dashboard and Netdata Cloud, all health alerts are configured _per node_ via individual Netdata Agents. If you want to deploy a new alert across your , you must configure each node with the same health configuration files. You do not need to restart the Netdata Agent between changes to health configuration files, such as specific health entities. Instead, you can use `netdatacli` and the `reload-health` option to prevent gaps in metrics collection. ```bash sudo netdatacli reload-health ``` If `netdatacli` doesn't work on your system, send a `SIGUSR2` signal to the daemon, which reloads health configuration without restarting the entire process. ```bash killall -USR2 netdata ``` You can configure the Agent's health watchdog service by editing files in two locations: The `[health]` section in `netdata.conf`. By editing the daemon's behavior, you can disable health monitoring altogether, run health checks more or less often, and more. See for a table of all the available settings, their default values, and what they control. The individual `.conf` files in `health.d/`. These health entity files are organized by the type of metric they are performing calculations on or their associated collector. You should edit these files using the `edit-config` script. For example: `sudo ./edit-config health.d/cpu.conf`. Navigate to your and use `edit-config` to make changes to any of these files. For example, to edit the `cpu.conf` health configuration file, run: ```bash sudo ./edit-config health.d/cpu.conf ``` Each health configuration file contains one or more health entities, which always begin with `alarm:` or `template:`. For example, here is the first health entity in `health.d/cpu.conf`: ```yaml template: 10mincpuusage on: system.cpu class: Utilization type: System component: CPU lookup: average -10m unaligned of user,system,softirq,irq,guest units: % every: 1m warn: $this > (($status >= $WARNING) ? (75) : (85)) crit: $this > (($status == $CRITICAL) ? (85) : (95)) delay: down 15m multiplier 1.5 max 1h summary: CPU utilization info: Average cpu utilization for the last 10 minutes (excluding iowait, nice and steal) to: sysadmin ``` To tune this alert to trigger warning and critical alerts at a lower CPU utilization, change the `warn` and `crit` lines to the values of your choosing. For example: ```yaml warn: $this > (($status >= $WARNING) ? (60) : (75)) crit: $this > (($status == $CRITICAL) ? (75) : (85)) ``` Save the file and to apply your changes. Alerts and notifications can be disabled permanently via configuration changes, or temporarily, via the . The available options are described below. In the `netdata.conf` `[health]` section, set `enabled` to `no`, and restart the agent. In the `netdata.conf` `[health]` section, set `enabled alarms` to a that excludes one or more alerts. e.g. `enabled alarms = !oomkill *` will load all alerts except `oomkill`. You can also , comment out its definition, and . You can stop receiving notification for an individual alert by the `to:` line to

```yaml to: silent ``` This action requires that you . When you need to frequently disable all or some alerts from triggering during certain times (for instance when running backups) you can use the . The API allows you to issue commands to control the health engine's behavior without changing configuration, or restarting the agent. If you want health checks to keep running and alerts to keep getting triggered, but notifications to be suppressed temporarily, you can use the . The API allows you to issue commands to control the health engine's behavior without changing configuration, or restarting the agent. While tuning existing alerts may work in some cases, you may need to write entirely new health entities based on how your systems, containers, and applications work. Read the for a full listing of the format, syntax, and functionality of health entities. To write a new health entity into a new file, navigate to your , then use `touch` to create a new file in the `health.d/` directory. Use `edit-config` to start editing the file. As an example, let's create a `ram-usage.conf` file. ```bash sudo touch health.d/ram-usage.conf sudo ./edit-config health.d/ram-usage.conf ``` For example, here is a health entity that triggers a warning alert when a node's RAM usage rises above 80%, and a critical alert above 90%: ```yaml alarm: ram_usage on: system.ram lookup: average -1m percentage of used units: % every: 1m warn: $this > 80 crit: $this > 90 info: The percentage of RAM being used by the system. ``` Let's look into each of the lines to see how they create a working health entity. `alarm`: The name for your new entity. The name needs to follow these requirements: Any alphabet letter or number. The symbols `.` and `_`. Cannot be `chart name`, `dimension name`, `family name`, or `chart variable names`. `on`: Which chart the entity listens to. `lookup`: Which metrics the alert monitors, the duration of time to monitor, and how to process the metrics into a usable format. `average`: Calculate the average of all the metrics collected. `-1m`: Use metrics from 1 minute ago until now to calculate that average. `percentage`: Clarify that we're calculating a percentage of RAM usage. `of used`: Specify which dimension (`used`) on the `system.ram` chart you want to monitor with this entity. `units`: Use percentages rather than absolute units. `every`: How often to perform the `lookup` calculation to decide whether to trigger this alert. `warn`/`crit`: The value at which Netdata should trigger a warning or critical alert. This example uses simple syntax, but most pre-configured health entities use to avoid superfluous notifications. `info`: A description of the alert, which will appear in the dashboard and notifications. In human-readable format: This health entity, named ram_usage, watches the system.ram chart. It looks up the last 1 minute of metrics from the used dimension and calculates the average of all those metrics in a percentage format, using a % unit. The entity performs this lookup every minute. If the average RAM usage percentage over the last 1 minute is more than 80%, the entity triggers a warning alert. If the usage is more than 90%, the entity triggers a critical alert. When you finish writing this new health entity, to see it live on the local dashboard or Netdata

The following reference contains information about the syntax and options of health entities, which Netdata attaches to charts in order to trigger alerts. There are two entity types: alarms and templates. They have the same format and feature setthe only difference is their label. Alerts are attached to specific charts and use the `alarm` label. Templates define rules that apply to all charts of a specific context, and use the `template` label. Templates help you apply one entity to all disks, all network interfaces, all MySQL databases, and so on. Alerts have higher precedence and will override templates. If the `alert` and `template` entities have the same name and are attached to the same chart, Netdata will use `alarm`. Netdata parses the following lines. Beneath the table is an in-depth explanation of each line's purpose and syntax. The `alarm` or `template` line must be the first line of any entity. The `on` line is always required. The `every` line is required if not using `lookup`. Each entity must have at least one of the following lines: `lookup`, `calc`, `warn`, or `crit`. A few lines use space-separated lists to define how the entity behaves. You can use `*` as a wildcard or prefix with `!` for a negative match. Order is important, too! See our for more examples. Lines terminated by a `\` are spliced together with the next line. The backslash is removed and the following line is joined with the current one. No space is inserted, so you may split a line anywhere, even in the middle of a word. This comes in handy if your `info` line consists of several sentences. | line | required | functionality | |--|--|| | | yes | Name of the alert/template. | | | yes | The chart this alert should attach to. | | | no | The general alert classification. | | | no | What area of the system the alert monitors. | | | no | Specific component of the type of the alert. | | | yes | The database lookup to find and process metrics for the chart specified through `on`. | | | yes (see above) | A calculation to apply to the value found via `lookup` or another variable. | | | no | The frequency of the alert. | | | no | Set the green and red thresholds of a chart. | | | yes (see above) | Expressions evaluating to true or false, and when true, will trigger the alert. | | | no | A list of roles to send notifications to. | | | no | The script to execute when the alert changes status. | | | no | Optional hysteresis settings to prevent floods of notifications. | | | no | The interval for sending notifications when an alert is in WARNING or CRITICAL mode. | | | no | Add an option to not clear alerts. | | | no | Restrict an alert or template to a list of matching labels present on a host. | | | no | Restrict an alert or template to a list of matching labels present on a chart. | | | no | A brief description of the

| | | no | A longer text field that provides more information of this alert | The `alarm` or `template` line must be the first line of any entity. This line starts an alert or template based on the you're interested in creating. Alert: ```yaml alarm: NAME ``` Template: ```yaml template: NAME ``` `NAME` can be any alpha character, with `.` (period) and `_` (underscore) as the only allowed symbols, but the names cannot be `chart name`, `dimension name`, `family name`, or `chart variables names`. This line defines the chart this alert should attach to. Alerts: ```yaml on: CHART ``` The value `CHART` should be the unique ID or name of the chart you're interested in, as shown on the dashboard. In the image below, the unique ID is `system.cpu`. Finding the unique ID of a chart Template: ```yaml on: CONTEXT ``` The value `CONTEXT` should be the context you want this template to attach to. Need to find the context? Hover over the date on any given chart and look at the tooltip. In the image below, which shows a disk I/O chart, the tooltip reads: `proc:/proc/diskstats, disk.io`. You're interested in what comes after the comma: `disk.io`. That's the name of the chart's context. If you create a template using the `disk.io` context, it will apply an alert to every disk available on your system. This indicates the type of error (or general problem area) that the alert or template applies to. For example, `Latency` can be used for alerts that trigger on latency issues on network interfaces, web servers, or database systems. Example: ```yaml class: Latency ``` <details> <summary>Netdata's stock alerts use the following `class` attributes by default:</summary> | Class | |-| | Errors | | Latency | | Utilization | | Workload | </details> `class` will default to `Unknown` if the line is missing from the alert configuration. Type can be used to indicate the broader area of the system that the alert applies to. For example, under the general `Database` type, you can group together alerts that operate on various database systems, like `MySQL`, `CockroachDB`, `CouchDB` etc. Example: ```yaml type: Database ``` <details> <summary>Netdata's stock alerts use the following `type` attributes by default, but feel free to adjust for your own requirements.</summary> | Type | Description | |--|| | Ad Filtering | Services related to Ad Filtering (like pi-hole) | | Certificates | Certificates monitoring related | | Cgroups | Alerts for cpu and memory usage of control groups | | Computing | Alerts for shared computing applications (e.g. boinc) | | Containers | Container related alerts (e.g. docker instances) | | Database | Database systems (e.g. MySQL, PostgreSQL, etc) | | Data Sharing | Used to group together alerts for data sharing applications | | DHCP | Alerts for dhcp related services | | DNS | Alerts for dns related services | | Kubernetes | Alerts for kubernetes nodes monitoring | | KV Storage | Key-Value pairs services alerts (e.g. memcached) | | Linux | Services specific to Linux (e.g. systemd) | | Messaging | Alerts for message passing services (e.g. vernemq) | | Netdata | Internal Netdata components monitoring | | Other | When an alert doesn't fit in other types. | | Power Supply | Alerts from power supply related services (e.g. apcupsd) | | Search engine | Alerts for search services

elasticsearch) | | Storage | Class for alerts dealing with storage services (storage devices typically live under `System`) | | System | General system alerts (e.g. cpu, network, etc.) | | Virtual Machine | Virtual Machine software | | Web Proxy | Web proxy software (e.g. squid) | | Web Server | Web server software (e.g. Apache, ngnix, etc.) | | Windows | Alerts for monitor of windows services | </details> If an alert configuration is missing the `type` line, its value will default to `Unknown`. Component can be used to narrow down what the previous `type` value specifies for each alert or template. Continuing from the previous example, `component` might include `MySQL`, `CockroachDB`, `MongoDB`, all under the same `Database` type. Example: ```yaml component: MySQL ``` As with the `class` and `type` line, if `component` is missing from the configuration, its value will default to `Unknown`. This line makes a database lookup to find a value. This result of this lookup is available as `$this`. The format is: ```yaml lookup: METHOD(GROUPING OPTIONS) AFTER [at BEFORE] [every DURATION] [OPTIONS] [of DIMENSIONS] ``` The full is supported. In short: `METHOD` is one of the available such as `average`, `min`, `max` etc. This is required. `GROUPING OPTIONS` are optional and can have the form `CONDITION VALUE`, where `CONDITION` is `!=`, `=`, `<=`, `<`, `>`, `>=` and `VALUE` is a number. The `CONDITION` and `VALUE` are required for `countif`, while `VALUE` is used by `percentile`, `trimmedmean` and `trimmedmedian`. `AFTER` is a relative number of seconds, but it also accepts a single letter for changing the units, like `-1s` = 1 second in the past, `-1m` = 1 minute in the past, `-1h` = 1 hour in the past, `-1d` = 1 day in the past. You need a negative number (i.e. how far in the past to look for the value). This is required. `at BEFORE` is by default 0 and is not required. Using this you can define the end of the lookup. So data will be evaluated between `AFTER` and `BEFORE`. `every DURATION` sets the updated frequency of the lookup (supports single letter units as above too). `OPTIONS` is a space separated list of `percentage`, `absolute`, `min`, `max`, `average`, `sum`, `min2max`, `unaligned`, `match-ids`, `match-names`. `percentage` during time-aggregation, calculate the percentage of the selected dimensions over the total of all dimensions. `absolute` during time-aggregation, turns all sample values positive before using them. `min` after time-aggregation of each dimension, return the minimum of all dimensions. `max` after time-aggregation of each dimension, return the maximum of all dimensions. `average` after time-aggregation of each dimension, return the average of all dimensions. `sum` after time-aggregation of each dimension, return the sum of all dimensions (this is the default). `min2max` after time-aggregation of each dimension, return the delta between the min and the max of the dimensions. `unaligned` prevents shifting the query window to multiples of the query duration. `match-ids` matches the dimensions based on their IDs (the default is enabled, give `match-names` to disable). `match-names` matches the dimension based on their names (the default is enabled, give `match-ids` to disable). `of DIMENSIONS` is optional and has to be the last parameter. Dimensions have to be separated by `,` or `|`. The space characters found in dimensions will be kept as-is (a few dimensions have spaces in their

This accepts Netdata simple patterns _(with `words` separated by `,` or `|` instead of spaces)_ and the `match-ids` and `match-names` options affect the searches for dimensions. The result of the lookup will be available as `$this` and `$NAME` in expressions. The timestamps of the timeframe evaluated by the database lookup is available as variables `$after` and `$before` (both are unix timestamps). A `calc` is designed to apply some calculation to the values or variables available to the entity. The result of the calculation will be made available at the `$this` variable, overwriting the value from your `lookup`, to use in warning and critical expressions. When paired with `lookup`, `calc` will perform the calculation just after `lookup` has retrieved a value from Netdata's database. You can use `calc` without `lookup` if you are using . The `calc` line uses for its syntax. ```yaml calc: EXPRESSION ``` Sets the update frequency of this alert. This is the same to the `every DURATION` given in the `lookup` lines. Format: ```yaml every: DURATION ``` `DURATION` accepts `s` for seconds, `m` is minutes, `h` for hours, `d` for days. Set the green and red thresholds of a chart. Both are available as `$green` and `$red` in expressions. If multiple alerts define different thresholds, the ones defined by the first alert will be used. Eventually it will be visualized on the dashboard, so only one set of them is allowed If you need multiple sets of them in different alerts, use absolute numbers instead of `$red` and `$green`. Format: ```yaml green: NUMBER red: NUMBER ``` Define the expression that triggers either a warning or critical alert. These are optional, and should evaluate to either true or false (or zero/non-zero). The format uses Netdata's . ```yaml warn: EXPRESSION crit: EXPRESSION ``` This will be the first script parameter that will be executed when the alert changes its status. Its meaning is left up to the `exec` script. The default `exec` script, `alarm-notify.sh`, uses this field as a space separated list of roles, which are then consulted to find the exact recipients per notification method. Format: ```yaml to: ROLE1 ROLE2 ROLE3 ... ``` Script to be executed when the alert status changes. Format: ```yaml exec: SCRIPT ``` The default `SCRIPT` is Netdata's `alarm-notify.sh`, which supports all the notifications methods Netdata supports, including custom hooks. This is used to provide optional hysteresis settings for the notifications, to defend against notification floods. These settings do not affect the actual alert - only the time the `exec` script is executed. Format: ```yaml delay: [[[up U] [down D] multiplier M] max X] ``` `up U` defines the delay to be applied to a notification for an alert that raised its status (i.e. CLEAR to WARNING, CLEAR to CRITICAL, WARNING to CRITICAL). For example, `up 10s`, the notification for this event will be sent 10 seconds after the actual event. This is used in hope the alert will get back to its previous state within the duration given. The default `U` is zero. `down D` defines the delay to be applied to a notification for an alert that moves to lower state (i.e. CRITICAL to WARNING, CRITICAL to CLEAR, WARNING to CLEAR). For example, `down 1m` will delay the notification by 1 minute. This is used to prevent notifications for flapping alerts. The default `D` is

`multiplier M` multiplies `U` and `D` when an alert changes state, while a notification is delayed. The default multiplier is `1.0`. `max X` defines the maximum absolute notification delay an alert may get. The default `X` is `max(U M, D M)` (i.e. the max duration of `U` or `D` multiplied once with `M`). Example: `delay: up 10s down 15m multiplier 2 max 1h` The time is `00:00:00` and the status of the alert is CLEAR. | time of event | new status | delay | notification will be sent | why | |||||-| | 00:00:01 | WARNING | `up 10s` | 00:00:11 | first state switch | | 00:00:05 | CLEAR | `down 15m x2` | 00:30:05 | the alert changes state while a notification is delayed, so it was multiplied | | 00:00:06 | WARNING | `up 10s x2 x2` | 00:00:26 | multiplied twice | | 00:00:07 | CLEAR | `down 15m x2 x2 x2` | 00:45:07 | multiplied 3 times. | So: `U` and `D` are multiplied by `M` every time the alert changes state (any state, not just their matching one) and a delay is in place. All are reset to their defaults when the alert switches state without a delay in place. Defines the interval between repeating notifications for the alerts in CRITICAL or WARNING mode. This will override the default interval settings inherited from health settings in `netdata.conf`. The default settings for repeating notifications are `default repeat warning = DURATION` and `default repeat critical = DURATION` which can be found in health stock configuration, when one of these interval is bigger than 0, Netdata will activate the repeat notification for `CRITICAL`, `CLEAR` and `WARNING` messages. Format: ```yaml repeat: [off] [warning DURATION] [critical DURATION] ``` `off`: Turns off the repeating feature for the current alert. This is effective when the default repeat settings has been enabled in health configuration. `warning DURATION`: Defines the interval when the alert is in WARNING state. Use `0s` to turn off the repeating notification for WARNING mode. `critical DURATION`: Defines the interval when the alert is in CRITICAL state. Use `0s` to turn off the repeating notification for CRITICAL mode. The only possible value for the `options` line is ```yaml options: no-clear-notification ``` For some alerts we need compare two time-frames, to detect anomalies. For example, `health.d/httpcheck.conf` has an alert template called `webserviceslow` that compares the average http call response time over the last 3 minutes, compared to the average over the last hour. It triggers a warning alert when the average of the last 3 minutes is twice the average of the last hour. In such cases, it is easy to trigger the alert, but difficult to tell when the alert is cleared. As time passes, the newest window moves into the older, so the average response time of the last hour will keep increasing. Eventually, the comparison will find the averages in the two time-frames close enough to clear the alert. However, the issue was not resolved, it's just a matter of the newer data "polluting" the old. For such alerts, it's a good idea to tell Netdata to not clear the notification, by using the `no-clear-notification` option. Defines the list of labels present on a host. See our for an explanation of host labels and how to implement them. For example, let's suppose that

is configured with the following labels: ```yaml [host labels] installed = 20191211 room = server ``` And more labels in `netdata.conf` for workstations: ```yaml [host labels] installed = 201705 room = workstation ``` By defining labels inside of `netdata.conf`, you can now apply labels to alerts. For example, you can add the following line to any alerts you'd like to apply to hosts that have the label `room = server`. ```yaml host labels: room = server ``` The `host labels` is a space-separated list that accepts simple patterns. For example, you can create an alert that will be applied to all hosts installed in the last decade with the following line: ```yaml host labels: installed = 201* ``` See our for more examples. Similar to host labels, the `chart labels` key can be used to filter if an alert will load or not for a specific chart, based on whether these chart labels match or not. The list of chart labels present on each chart can be obtained from http://localhost:19999/api/v1/charts?all For example, each `diskspace` chart defines a chart label called `mountpoint` with each instance of this chart having a value there of which mount point it monitors. If you have an e.g. external disk mounted on `/mnt/disk1` and you don't wish any related disk space alerts running for it (but you do for all other mount points), you can add the following to the alert's configuration: ```yaml chart labels: mount_point=!/mnt/disk1 * ``` The `chart labels` is a space-separated list that accepts simple patterns. If you use multiple different chart labels, then the result is an AND between them. i.e. the following: ```yaml chart labels: mount_point=/mnt/disk1 device=sda ``` Will create the alert if the `mount_point` is `/mnt/disk1` and the `device` is `sda`. Furthermore, if a chart label name is specified that does not exist in the chart, the chart won't be matched. See our for more examples. The summary field contains a brief title of the alert. It is used as the subject for the notifications, and in dashboard list of alerts. An example for the `ram_available` alert is: ```yaml summary: Available Ram ``` summary fields can contain special variables in their text that will be replaced during run-time to provide more specific alert information. Current variables supported are: | variable | description | ||-| | ${family} | Will be replaced by the family instance for the alert (e.g. eth0) | | ${label:LABEL_NAME} | The variable will be replaced with the value of the chart label | For example, a summary field like the following: ```yaml summary: 1 minute received traffic overflow for ${label:device} ``` Will be rendered on the alert acting on interface `eth0` as: ```yaml summary: 1 minute received traffic overflow for eth0 ``` Please note that variable names are case-sensitive. The info field can contain a small piece of text describing the alert or template. This will be rendered in notifications and UI elements whenever the specific alert is in focus. An example for the `ram_available` alert is: ```yaml info: Percentage of estimated amount of RAM available for userspace processes, without causing swapping ``` info fields can contain special variables in their text that will be replaced during run-time to provide more specific alert

Current variables supported are: | variable | description | ||-| | ${family} | Will be replaced by the family instance for the alert (e.g. eth0) | | ${label:LABEL_NAME} | The variable will be replaced with the value of the chart label | For example, an info field like the following: ```yaml info: average inbound utilization for the network interface ${family} over the last minute ``` Will be rendered on the alert acting on interface `eth0` as: ```yaml info: average inbound utilization for the network interface eth0 over the last minute ``` An alert acting on a chart that has a chart label named e.g. `target`, with a value of `https://netdata.cloud/`, can be enriched as follows: ```yaml info: average ratio of HTTP responses with unexpected status over the last 5 minutes for the site ${label:target} ``` Will become: ```yaml info: average ratio of HTTP responses with unexpected status over the last 5 minutes for the site https://netdata.cloud/ ``` Please note that variable names are case-sensitive. Netdata has an internal infix expression parser under `libnetdata/eval`. This parses expressions and creates an internal structure that allows fast execution of them. These operators are supported `+`, `-`, `*`, `/`, `<`, `==`, `<=`, `<>`, `!=`, `>`, `>=`, `&&`, `||`, `!`, `AND`, `OR`, `NOT`. Boolean operators result in either `1` (true) or `0` (false). The conditional evaluation operator `?` is supported too. Using this operator IF-THEN-ELSE conditional statements can be specified. The format is: `(condition) ? (true expression) : (false expression)`. So, Netdata will first evaluate the `condition` and based on the result will either evaluate `true expression` or `false expression`. Example: `($this > 0) ? ($avail * 2) : ($used / 2)`. Nested such expressions are also supported (i.e. `true expression` and `false expression` can contain conditional evaluations). Expressions also support the `abs()` function. Expressions can have variables. Variables start with `$`. Check below for more information. There are two special values you can use: `nan`, for example `$this != nan` will check if the variable `this` is available. A variable can be `nan` if the database lookup failed. All calculations (i.e. addition, multiplication, etc.) with a `nan` result in a `nan`. `inf`, for example `$this != inf` will check if `this` is not infinite. A value or variable can be set to infinite if divided by zero. All calculations (i.e. addition, multiplication, etc.) with a `inf` result in a `inf`. A common (but not necessarily obvious) use of the conditional evaluation operator is to provide around the critical or warning thresholds. This usage helps to avoid bogus messages resulting from small variations in the value when it is varying regularly but staying close to the threshold value, without needing to delay sending messages at all. An example of such usage from the default CPU usage alerts bundled with Netdata is: ```yaml warn: $this > (($status >= $WARNING) ? (75) : (85)) crit: $this > (($status == $CRITICAL) ? (85) : (95)) ``` The above say: If the alert is currently a warning, then the threshold for being considered a warning is 75, otherwise it's 85. If the alert is currently critical, then the threshold for being considered critical is 85, otherwise it's 95. Which in turn, results in the following behavior: While the value is rising, it will trigger a warning when it exceeds 85, and a critical alert when it exceeds

While the value is falling, it will return to a warning state when it goes below 85, and a normal state when it goes below 75. If the value is constantly varying between 80 and 90, then it will trigger a warning the first time it goes above 85, but will remain a warning until it goes below 75 (or goes above 85). If the value is constantly varying between 90 and 100, then it will trigger a critical alert the first time it goes above 95, but will remain a critical alert goes below 85 (at which point it will return to being a warning). You can find all the variables that can be used for a given chart, using `http://NODE:19999/api/v1/alarmvariables?chart=CHARTNAME`, replacing `NODE` with the IP address or hostname for your Agent dashboard. For example, [variables for the `system.cpu` chart of the registry](https://registry.my-netdata.io/api/v1/alarm_variables?chart=system.cpu). If you don't know how to find the CHART_NAME, you can read about it . Netdata supports 3 internal indexes for variables that will be used in health monitoring. <details><summary>The variables below can be used in both chart alerts and context templates.</summary> Although the `alarm_variables` link shows you variables for a particular chart, the same variables can also be used in templates for charts belonging to a given . The reason is that all charts of a given context are essentially identical, with the only difference being the family that identifies a particular hardware or software instance. </details> chart local variables. All the dimensions of the chart are exposed as local variables. The value of `$this` for the other configured alerts of the chart also appears, under the name of each configured alert. Charts also define a few special variables: `$lastcollectedt` is the unix timestamp of the last data collection `$collectedtotalraw` is the sum of all the dimensions (their last collected values) `$update_every` is the update frequency of the chart `$green` and `$red` the threshold defined in alerts (these are per chart - the charts inherits them from the first alert that defined them) > Chart dimensions define their last calculated (i.e. interpolated) value, exactly as shown on the charts, but also a variable with their name and suffix `_raw` that resolves to the last collected value - as collected and another with suffix `lastcollected_t` that resolves to unix timestamp the dimension was last collected (there may be dimensions that fail to be collected while others continue normally). host variables. All the dimensions of all charts, including all alerts, in fullname. Fullname is `CHART.VARIABLE`, where `CHART` is either the chart id or the chart name (both are supported). special variables are: `$this`, which is resolved to the value of the current alert. `$status`, which is resolved to the current status of the alert (the current = the last status, i.e. before the current database lookup and the evaluation of the `calc` line). This values can be compared with `$REMOVED`, `$UNINITIALIZED`, `$UNDEFINED`, `$CLEAR`, `$WARNING`, `$CRITICAL`. These values are incremental, e.g. `$status > $CLEAR` works as expected. `$now`, which is resolved to current unix timestamp. Alerts can have the following statuses: `REMOVED` - the alert has been deleted (this happens when a SIGUSR2 is sent to Netdata to reload health configuration) `UNINITIALIZED` - the alert is not initialized yet `UNDEFINED` - the alert failed to be calculated (i.e. the database lookup failed, a division by zero occurred,

`CLEAR` - the alert is not armed / raised (i.e. is OK) `WARNING` - the warning expression resulted in true or non-zero `CRITICAL` - the critical expression resulted in true or non-zero The external script will be called for all status changes. Check the `health/health.d/` directory for all alerts shipped with Netdata. Here are a few examples: A simple check if an apache server is alive: ```yaml template: apachelastcollected_secs on: apache.requests calc: $now - $lastcollectedt every: 10s warn: $this > ( 5 * $update_every) crit: $this > (10 * $update_every) ``` The above checks that Netdata is able to collect data from apache. In detail: ```yaml template: apachelastcollected_secs ``` The above defines a template named `apachelastcollected_secs`. The name is important since `$apachelastcollected_secs` resolves to the `calc` line. So, try to give something descriptive. ```yaml on: apache.requests ``` The above applies the template to all charts that have `context = apache.requests` (i.e. all your apache servers). ```yaml calc: $now - $lastcollectedt ``` `$now` is a standard variable that resolves to the current timestamp. `$lastcollectedt` is the last data collection timestamp of the chart. So this calculation gives the number of seconds passed since the last data collection. ```yaml every: 10s ``` The alert will be evaluated every 10 seconds. ```yaml warn: $this > ( 5 * $update_every) crit: $this > (10 * $update_every) ``` If these result in non-zero or true, they trigger the alert. `$this` refers to the value of this alert (e.g. the result of the `calc` line). We could also use `$apachelastcollected_secs`. `$update_every` is the update frequency of the chart, in seconds. So, the warning condition checks if we have not collected data from apache for 5 iterations and the critical condition checks for 10 iterations. Check if any of the disks is critically low on disk space: ```yaml template: diskfullpercent on: disk.space calc: $used * 100 / ($avail + $used) every: 1m warn: $this > 80 crit: $this > 95 repeat: warning 120s critical 10s ``` `$used` and `$avail` are the `used` and `avail` chart dimensions as shown on the dashboard. So, the `calc` line finds the percentage of used space. `$this` resolves to this percentage. This is a repeating alert and if the alert becomes CRITICAL it repeats the notifications every 10 seconds. It also repeats notifications every 2 minutes if the alert goes into WARNING mode. Predict if any disk will run out of space in the near future. We do this in 2 steps: Calculate the disk fill rate: ```yaml template: diskfillrate on: disk.space lookup: max -1s at -30m unaligned of avail calc: ($this - $avail) / (30 * 60) every: 15s ``` In the `calc` line: `$this` is the result of the `lookup` line (i.e. the free space 30 minutes ago) and `$avail` is the current disk free space. So the `calc` line will either have a positive number of GB/second if the disk is filling up, or a negative number of GB/second if the disk is freeing up space. There is no `warn` or `crit` lines here. So, this template will just do the calculation and nothing more. Predict the hours after which the disk will run out of space: ```yaml template: diskfullafter_hours on:

calc: $avail / $diskfillrate / 3600 every: 10s warn: $this > 0 and $this < 48 crit: $this > 0 and $this < 24 ``` The `calc` line estimates the time in hours, we will run out of disk space. Of course, only positive values are interesting for this check, so the warning and critical conditions check for positive values and that we have enough free space for 48 and 24 hours respectively. Once this alert triggers we will receive an email like this: Check if any network interface is dropping packets: ```yaml template: 30minpacketdrops on: net.drops lookup: sum -30m unaligned absolute every: 10s crit: $this > 0 ``` The `lookup` line will calculate the sum of the all dropped packets in the last 30 minutes. The `crit` line will issue a critical alert if even a single packet has been dropped. Note that the drops chart does not exist if a network interface has never dropped a single packet. When Netdata detects a dropped packet, it will add the chart, and it will automatically attach this alert to it. Derive a "" based alert on `user` dimension of the `system.cpu` chart: ```yaml alarm: cpuusermean on: system.cpu lookup: mean -60s of user every: 10s alarm: cpuuserstddev on: system.cpu lookup: stddev -60s of user every: 10s alarm: cpuuserzscore on: system.cpu lookup: mean -10s of user calc: ($this - $cpuusermean) / $cpuuserstddev every: 10s warn: $this < -2 or $this > 2 crit: $this < -3 or $this > 3 ``` Since we create two input alerts, one for `mean` and one for `stddev` and then use them both as inputs in our final `cpuuserzscore` alert. Warning if 5 minute rolling averaged across all CPU dimensions is above 5%, critical if it goes above 20%: ```yaml template: ml5mincpu_chart on: system.cpu lookup: average -5m anomaly-bit of * calc: $this units: % every: 30s warn: $this > (($status >= $WARNING) ? (5) : (20)) crit: $this > (($status == $CRITICAL) ? (20) : (100)) info: rolling 5min anomaly rate for system.cpu chart ``` The `lookup` line will calculate the average anomaly rate across all `system.cpu` dimensions over the last 5 minues. In this case Netdata will create one alert for the chart. Warning if 5 minute rolling averaged across all ML enabled dimensions is above 5%, critical if it goes above 20%: ```yaml template: ml5minnode on: anomalydetection.anomalyrate lookup: average -5m of anomaly_rate calc: $this units: % every: 30s warn: $this > (($status >= $WARNING) ? (5) : (20)) crit: $this > (($status == $CRITICAL) ? (20) : (100)) info: rolling 5min anomaly rate for all ML enabled dims ``` The `lookup` line will use the `anomalyrate` dimension of the `anomalydetection.anomaly_rate` ML chart to calculate the average over the last 5 minutes. You can compile Netdata with and then set in `netdata.conf`: ```yaml [global] debug flags = 0x0000000000800000 ``` Then check your `/var/log/netdata/debug.log`. It will show you how it works. Important: this will generate a lot of output in debug.log. You can find the context of charts by looking up the chart in either `http://NODE:19999/netdata.conf` or `http://NODE:19999/api/v1/charts`, replacing `NODE` with the IP address or hostname for your Agent dashboard. You can find how Netdata interpreted the expressions by examining the alert at `http://NODE:19999/api/v1/alarms?all`. For each expression, Netdata will return the expression as given in its config file, and the same expression with additional parentheses added to indicate the evaluation flow of the expression.