Health configuration reference

Welcome to the health configuration reference.

This guide contains information about editing health configuration files to tweak existing alarms or create new health entities that are customized to the needs of your infrastructure.

To learn the basics of locating and editing health configuration files, see the health quickstart.

Health configuration files

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 daemon configuration 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.

Health entity reference

The following reference contains information about the syntax and options of health entities, which Netdata attaches to charts in order to trigger alarms.

Entity types

There are two entity types: alarms and templates. They have the same format and feature set—the only difference is their label.

Alarms 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.

Alarms have higher precedence and will override templates. If an alarm and template entity have the same name and attach to the same chart, Netdata will use the alarm.

Entity format

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 simple patterns docs 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
alarm/template	yes	Name of the alarm/template.
on	yes	The chart this alarm should attach to.
class	no	The general alarm classification.
type	no	What area of the system the alarm monitors.
component	no	Specific component of the type of the alarm.
os	no	Which operating systems to run this chart.
hosts	no	Which hostnames will run this alarm.
plugin	no	Restrict an alarm or template to only a certain plugin.
module	no	Restrict an alarm or template to only a certain module.
charts	no	Restrict an alarm or template to only certain charts.
families	no	Restrict a template to only certain families.
lookup	yes	The database lookup to find and process metrics for the chart specified through on.
calc	yes (see above)	A calculation to apply to the value found via lookup or another variable.
every	no	The frequency of the alarm.
green/red	no	Set the green and red thresholds of a chart.
warn/crit	yes (see above)	Expressions evaluating to true or false, and when true, will trigger the alarm.
to	no	A list of roles to send notifications to.
exec	no	The script to execute when the alarm changes status.
delay	no	Optional hysteresis settings to prevent floods of notifications.
repeat	no	The interval for sending notifications when an alarm is in WARNING or CRITICAL mode.
options	no	Add an option to not clear alarms.
host labels	no	List of labels present on a host.
info	no	A brief description of the alarm.

The alarm or template line must be the first line of any entity.

Alarm line alarm or template

This line starts an alarm or template based on the entity type you're interested in creating.

Alarm:

alarm: NAME

Template:

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.

Alarm line on

This line defines the chart this alarm should attach to.

Alarms:

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.

Template:

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 alarm to every disk available on your system.

Alarm line class

This indicates the type of error (or general problem area) that the alarm or template applies to. For example, Latency can be used for alarms that trigger on latency issues on network interfaces, web servers, or database systems. Example:

class: Latency

Netdata's stock alarms use the following `class` attributes by default:

Class
Errors
Latency
Utilization
Workload

class will default to Unknown if the line is missing from the alarm configuration.

Alarm line type

Type can be used to indicate the broader area of the system that the alarm applies to. For example, under the general Database type, you can group together alarms that operate on various database systems, like MySQL, CockroachDB, CouchDB etc. Example:

type: Database

Netdata's stock alarms use the following `type` attributes by default, but feel free to adjust for your own requirements.

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 (e.g. elasticsearch)
Storage	Class for alerts dealing with storage services (storage devices typically live under System)
System	General system alarms (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 wmi services

If an alarm configuration is missing the type line, its value will default to Unknown.

Alarm line component

Component can be used to narrow down what the previous type value specifies for each alarm or template. Continuing from the previous example, component might include MySQL, CockroachDB, MongoDB, all under the same Database type. Example:

component: MySQL

As with the class and type line, if component is missing from the configuration, its value will default to Unknown.

Alarm line os

The alarm or template will be used only if the operating system of the host matches this list specified in os. The value is a space-separated list.

The following example enables the entity on Linux, FreeBSD, and macOS, but no other operating systems.

os: linux freebsd macos

Alarm line hosts

The alarm or template will be used only if the hostname of the host matches this space-separated list.

The following example will load on systems with the hostnames server and server2, and any system with hostnames that begin with database. It will not load on the host redis3, but will load on any other systems with hostnames that begin with redis.

hosts: server1 server2 database* !redis3 redis*

Alarm line plugin

The plugin line filters which plugin within the context this alarm should apply to. The value is a space-separated list of simple patterns. For example, you can create a filter for an alarm that applies specifically to python.d.plugin:

plugin: python.d.plugin

The plugin line is best used with other options like module. When used alone, the plugin line creates a very inclusive filter that is unlikely to be of much use in production. See module for a comprehensive example using both.

Alarm line module

The module line filters which module within the context this alarm should apply to. The value is a space-separated list of simple patterns. For example, you can create an alarm that applies only on the isc_dhcpd module started by python.d.plugin:

plugin: python.d.plugin
module: isc_dhcpd

Alarm line charts

The charts line filters which chart this alarm should apply to. It is only available on entities using the template line. The value is a space-separated list of simple patterns. For example, a template that applies to disk.svctm (Average Service Time) context, but excludes the disk sdb from alarms:

template: disk_svctm_alarm
      on: disk.svctm
  charts: !*sdb* *

Alarm line families

The families line, used only alongside templates, filters which families within the context this alarm should apply to. The value is a space-separated list.

The value is a space-separate list of simple patterns. See our simple patterns docs for some examples.

For example, you can create a template on the disk.io context, but filter it to only the sda and sdb families:

families: sda sdb

Alarm line lookup

This line makes a database lookup to find a value. This result of this lookup is available as $this.

The format is:

lookup: METHOD AFTER [at BEFORE] [every DURATION] [OPTIONS] [of DIMENSIONS] [foreach DIMENSIONS]

Everything is the same with badges. In short:

• METHOD is one of average, min, max, sum, incremental-sum. This is required.

• 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, min2max, unaligned, match-ids, match-names. Check the badges documentation for more info.

• 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 names). 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.

• foreach DIMENSIONS is optional, will always be the last parameter, and uses the same ,/| rules as the of parameter. Each dimension you specify in foreach will use the same rule to trigger an alarm. If you set both of and foreach, Netdata will ignore the of parameter and replace it with one of the dimensions you gave to foreach.

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).

Alarm line calc

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 other available variables.

The calc line uses expressions for its syntax.

calc: EXPRESSION

Alarm line every

Sets the update frequency of this alarm. This is the same to the every DURATION given in the lookup lines.

Format:

every: DURATION

DURATION accepts s for seconds, m is minutes, h for hours, d for days.

Alarm lines green and red

Set the green and red thresholds of a chart. Both are available as $green and $red in expressions. If multiple alarms define different thresholds, the ones defined by the first alarm will be used. These will eventually visualized on the dashboard, so only one set of them is allowed. If you need multiple sets of them in different alarms, use absolute numbers instead of $red and $green.

Format:

green: NUMBER
red: NUMBER

Alarm lines warn and crit

Define the expression that triggers either a warning or critical alarm. These are optional, and should evaluate to either true or false (or zero/non-zero).

The format uses Netdata's expressions syntax.

warn: EXPRESSION
crit: EXPRESSION

Alarm line to

This will be the first parameter of the script to be executed when the alarm switches 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:

to: ROLE1 ROLE2 ROLE3 ...

Alarm line exec

The script that will be executed when the alarm changes status.

Format:

exec: SCRIPT

The default SCRIPT is Netdata's alarm-notify.sh, which supports all the notifications methods Netdata supports, including custom hooks.

Alarm line delay

This is used to provide optional hysteresis settings for the notifications, to defend against notification floods. These settings do not affect the actual alarm - only the time the exec script is executed.

Format:

delay: [[[up U] [down D] multiplier M] max X]

• up U defines the delay to be applied to a notification for an alarm 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 alarm 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 alarm 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 alarms. The default D is zero.

• multiplier M multiplies U and D when an alarm changes state, while a notification is delayed. The default multiplier is 1.0.

• max X defines the maximum absolute notification delay an alarm 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 alarm 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 alarm 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 alarm changes state (any state, not just their matching one) and a delay is in place.
  • All are reset to their defaults when the alarm switches state without a delay in place.

Alarm line repeat

Defines the interval between repeating notifications for the alarms 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:

repeat: [off] [warning DURATION] [critical DURATION]

• off: Turns off the repeating feature for the current alarm. This is effective when the default repeat settings has been enabled in health configuration.
• warning DURATION: Defines the interval when the alarm is in WARNING state. Use 0s to turn off the repeating notification for WARNING mode.
• critical DURATION: Defines the interval when the alarm is in CRITICAL state. Use 0s to turn off the repeating notification for CRITICAL mode.

Alarm line options

The only possible value for the options line is

options: no-clear-notification

For some alarms we need compare two time-frames, to detect anomalies. For example, health.d/httpcheck.conf has an alarm template called web_service_slow 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 alarm 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 alarm, but difficult to tell when the alarm 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 alarm. However, the issue was not resolved, it's just a matter of the newer data "polluting" the old. For such alarms, it's a good idea to tell Netdata to not clear the notification, by using the no-clear-notification option.

Alarm line host labels

Defines the list of labels present on a host. See our host labels guide for an explanation of host labels and how to implement them.

For example, let's suppose that netdata.conf is configured with the following labels:

[host labels]
    installed = 20191211
    room = server

And more labels in netdata.conf for workstations:

[host labels]
    installed = 201705
    room = workstation

By defining labels inside of netdata.conf, you can now apply labels to alarms. For example, you can add the following line to any alarms you'd like to apply to hosts that have the label room = server.

host labels: room = server

The host labels is a space-separated list that accepts simple patterns. For example, you can create an alarm that will be applied to all hosts installed in the last decade with the following line:

host labels: installed = 201*

See our simple patterns docs for more examples.

Alarm line info

The info field can contain a small piece of text describing the alarm or template. This will be rendered in notifications and UI elements whenever the specific alarm is in focus. An example for the ram_available alarm is:

info: percentage of estimated amount of RAM available for userspace processes, without causing swapping

Expressions

Netdata has an internal infix expression parser. 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.

Special use of the conditional operator

A common (but not necessarily obvious) use of the conditional evaluation operator is to provide hysteresis 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 alarms bundled with Netdata is:

warn: $this > (($status >= $WARNING)  ? (75) : (85))
crit: $this > (($status == $CRITICAL) ? (85) : (95))

The above say:

• If the alarm is currently a warning, then the threshold for being considered a warning is 75, otherwise it's 85.

• If the alarm 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 95.

• 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).

Variables

You can find all the variables that can be used for a given chart, using http://NODE:19999/api/v1/alarm_variables?chart=CHART_NAME, replacing NODE with the IP address or hostname for your Agent dashboard. For example, variables for the system.cpu chart of the registry.

If you don't know how to find the CHART_NAME, you can read about it here.

Netdata supports 3 internal indexes for variables that will be used in health monitoring.

The variables below can be used in both chart alarms and context templates.

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 context. 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. Charts and templates do not apply to specific families anyway, unless if you explicitly limit an alarm with the alarm line families.

• chart local variables. All the dimensions of the chart are exposed as local variables. The value of $this for the other configured alarms of the chart also appears, under the name of each configured alarm.

  Charts also define a few special variables:

  • $last_collected_t is the unix timestamp of the last data collection

  • $collected_total_raw 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 alarms (these are per chart - the charts inherits them from the the first alarm 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 _last_collected_t that resolves to unix timestamp the dimension was last collected (there may be dimensions that fail to be collected while others continue normally).

• family variables. Families are used to group charts together. For example all eth0 charts, have family = eth0. This index includes all local variables, but if there are overlapping variables, only the first are exposed.

• host variables. All the dimensions of all charts, including all alarms, 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 alarm.

  • $status, which is resolved to the current status of the alarm (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, ie. $status > $CLEAR works as expected.

  • $now, which is resolved to current unix timestamp.

Alarm statuses

Alarms can have the following statuses:

• REMOVED - the alarm has been deleted (this happens when a SIGUSR2 is sent to Netdata to reload health configuration)

• UNINITIALIZED - the alarm is not initialized yet

• UNDEFINED - the alarm failed to be calculated (i.e. the database lookup failed, a division by zero occurred, etc)

• CLEAR - the alarm 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.

Example alarms

Check the health/health.d/ directory for all alarms shipped with Netdata.

Here are a few examples:

Example 1 - check server alive

A simple check if an apache server is alive:

template: apache_last_collected_secs
      on: apache.requests
    calc: $now - $last_collected_t
   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:

template: apache_last_collected_secs

The above defines a template named apache_last_collected_secs. The name is important since $apache_last_collected_secs resolves to the calc line. So, try to give something descriptive.

      on: apache.requests

The above applies the template to all charts that have context = apache.requests (i.e. all your apache servers).

    calc: $now - $last_collected_t

• $now is a standard variable that resolves to the current timestamp.

• $last_collected_t is the last data collection timestamp of the chart. So this calculation gives the number of seconds passed since the last data collection.

   every: 10s

The alarm will be evaluated every 10 seconds.

    warn: $this > ( 5 * $update_every)
    crit: $this > (10 * $update_every)

If these result in non-zero or true, they trigger the alarm.

• $this refers to the value of this alarm (i.e. the result of the calc line. We could also use $apache_last_collected_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.

Example 2 - disk space

Check if any of the disks is critically low on disk space:

template: disk_full_percent
      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 alarm and if the alarm becomes CRITICAL it repeats the notifications every 10 seconds. It also repeats notifications every 2 minutes if the alarm goes into WARNING mode.

Example 3 - disk fill rate

Predict if any disk will run out of space in the near future.

We do this in 2 steps:

Calculate the disk fill rate:

    template: disk_fill_rate
          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 if 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:

    template: disk_full_after_hours
          on: disk.space
        calc: $avail / $disk_fill_rate / 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 alarm triggers we will receive an email like this:

Example 4 - dropped packets

Check if any network interface is dropping packets:

template: 30min_packet_drops
      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 alarm 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 alarm to it.

Example 5 - CPU usage

Check if user or system dimension is using more than 50% of cpu:

 alarm: dim_template
    on: system.cpu
    os: linux
lookup: average -3s percentage foreach system,user
 units: %
 every: 10s
  warn: $this > 50
  crit: $this > 80

The lookup line will calculate the average CPU usage from system and user in the last 3 seconds. Because we have the foreach in the lookup line, Netdata will create two independent alarms called dim_template_system and dim_template_user that will have all the other parameters shared among them.

Example 6 - CPU usage

Check if all dimensions are using more than 50% of cpu:

 alarm: dim_template
    on: system.cpu
    os: linux
lookup: average -3s percentage foreach *
 units: %
 every: 10s
  warn: $this > 50
  crit: $this > 80

The lookup line will calculate the average of CPU usage from system and user in the last 3 seconds. In this case Netdata will create alarms for all dimensions of the chart.

Example 7 - Z-Score based alarm

Derive a "Z Score" based alarm on user dimension of the system.cpu chart:

 alarm: cpu_user_mean
    on: system.cpu
lookup: mean -60s of user
 every: 10s

 alarm: cpu_user_stddev
    on: system.cpu
lookup: stddev -60s of user
 every: 10s

 alarm: cpu_user_zscore
    on: system.cpu
lookup: mean -10s of user
  calc: ($this - $cpu_user_mean) / $cpu_user_stddev
 every: 10s
  warn: $this < -2 or $this > 2
  crit: $this < -3 or $this > 3

Since z = (x - mean) / stddev we create two input alarms, one for mean and one for stddev and then use them both as inputs in our final cpu_user_zscore alarm.

Troubleshooting

You can compile Netdata with debugging and then set in netdata.conf:

[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 alarm 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.

Disabling health checks or silencing notifications at runtime

It's currently not possible to schedule notifications from within the alarm template. For those scenarios where you need to temporary disable notifications (for instance when running backups triggers a disk alert) you can disable or silence notifications are runtime. The health checks can be controlled at runtime via the health management api.