19. Language Reference

19.1. Object Definition

Icinga 2 features an object-based configuration format. You can define new objects using the object keyword:

object Host "host1.example.org" {
  display_name = "host1"

  address = ""
  address6 = "::1"

In general you need to write each statement on a new line. Expressions started with {, ( and [ extend until the matching closing character and can be broken up into multiple lines.

Alternatively you can write multiple statements on a single line by separating them with a semicolon:

object Host "host1.example.org" {
  display_name = "host1"

  address = ""; address6 = "::1"

Each object is uniquely identified by its type (Host) and name (host1.example.org). Some types have composite names, e.g. the Service type which uses the host_name attribute and the name you specified to generate its object name.

Exclamation marks (!) are not permitted in object names.

Objects can contain a comma-separated list of property declarations. Instead of commas semicolons may also be used. The following data types are available for property values:

All objects have at least the following attributes:

Attribute Description
name The name of the object. This attribute can be modified in the object definition to override the name specified with the object directive.
type The type of the object.

19.2. Expressions

The following expressions can be used on the right-hand side of assignments.

19.2.1. Numeric Literals

A floating-point number.



19.2.2. Duration Literals

Similar to floating-point numbers except for the fact that they support suffixes to help with specifying time durations.



Supported suffixes include ms (milliseconds), s (seconds), m (minutes), h (hours) and d (days).

Duration literals are converted to seconds by the config parser and are treated like numeric literals.

19.2.3. String Literals

A string.


"Hello World!"

Certain characters need to be escaped. The following escape sequences are supported:

Character Escape sequence
" \"
\ \\
<TAB> \t
<BEL> \b

In addition to these pre-defined escape sequences you can specify arbitrary ASCII characters using the backslash character (\) followed by an ASCII character in octal encoding.

19.2.4. Multi-line String Literals

Strings spanning multiple lines can be specified by enclosing them in {{{ and }}}.


a multi-line

Unlike in ordinary strings special characters do not have to be escaped in multi-line string literals.

19.2.5. Boolean Literals

The keywords true and false are used to denote truth values.

19.2.6. Null Value

The null keyword can be used to specify an empty value.

19.2.7. Dictionary

An unordered list of key-value pairs. Keys must be unique and are compared in a case-sensitive manner.

Individual key-value pairs must either be comma-separated or on separate lines. The comma after the last key-value pair is optional.


  address = ""
  port = 443

Identifiers may not contain certain characters (e.g. space) or start with certain characters (e.g. digits). If you want to use a dictionary key that is not a valid identifier, you can enclose the key in double quotes.

19.2.8. Array

An ordered list of values.

Individual array elements must be comma-separated. The comma after the last element is optional.


[ "hello", 42 ]

An array may simultaneously contain values of different types, such as strings and numbers.

19.2.9. Operators

The following operators are supported in expressions. The operators are by descending precedence.

Operator Precedence Examples (Result) Description
() 1 (3 + 3) * 5 Groups sub-expressions
() 1 Math.random() Calls a function
[] 1 a[3] Array subscript
. 1 a.b Element access
! 2 !"Hello" (false), !false (true) Logical negation of the operand
~ 2 ~true (false) Bitwise negation of the operand
+ 2 +3 Unary plus
- 2 -3 Unary minus
* 3 5m * 10 (3000) Multiplies two numbers
/ 3 5m / 5 (60) Divides two numbers
% 3 17 % 12 (5) Remainder after division
+ 4 1 + 3 (4), "hello " + "world" ("hello world") Adds two numbers; concatenates strings
- 4 3 - 1 (2) Subtracts two numbers
<< 5 4 << 8 (1024) Left shift
>> 5 1024 >> 4 (64) Right shift
< 6 3 < 5 (true) Less than
> 6 3 > 5 (false) Greater than
<= 6 3 <= 3 (true) Less than or equal
>= 6 3 >= 3 (true) Greater than or equal
in 7 "foo" in [ "foo", "bar" ] (true) Element contained in array
!in 7 "foo" !in [ "bar", "baz" ] (true) Element not contained in array
== 8 "hello" == "hello" (true), 3 == 5 (false) Equal to
!= 8 "hello" != "world" (true), 3 != 3 (false) Not equal to
& 9 7 & 3 (3) Binary AND
^ 10 17 ^ 12 (29) Bitwise XOR
| 11 2 | 3 (3) Binary OR
&& 13 true && false (false), 3 && 7 (7), 0 && 7 (0) Logical AND
|| 14 true || false (true), 0 || 7 (7) Logical OR
= 12 a = 3 Assignment
=> 15 x => x * x (function with arg x) Lambda, for loop

19.2.10. Function Calls

Functions can be called using the () operator:

const MyGroups = [ "test1", "test" ]

  check_interval = len(MyGroups) * 1m

A list of available functions is available in the Library Reference chapter.

19.3. Assignments

In addition to the = operator shown above a number of other operators to manipulate attributes are supported. Here's a list of all available operators:

19.3.1. Operator =

Sets an attribute to the specified value.


  a = 5
  a = 7

In this example a has the value 7 after both instructions are executed.

19.3.2. Operator +=

The += operator is a shortcut. The following expression:

  a = [ "hello" ]
  a += [ "world" ]

is equivalent to:

  a = [ "hello" ]
  a = a + [ "world" ]

19.3.3. Operator -=

The -= operator is a shortcut. The following expression:

  a = 10
  a -= 5

is equivalent to:

  a = 10
  a = a - 5

19.3.4. Operator \*=

The *= operator is a shortcut. The following expression:

  a = 60
  a *= 5

is equivalent to:

  a = 60
  a = a * 5

19.3.5. Operator /=

The /= operator is a shortcut. The following expression:

  a = 300
  a /= 5

is equivalent to:

  a = 300
  a = a / 5

19.4. Indexer

The indexer syntax provides a convenient way to set dictionary elements.


  hello.key = "world"

Example (alternative syntax):

  hello["key"] = "world"

This is equivalent to writing:

  hello += {
    key = "world"

If the hello attribute does not already have a value, it is automatically initialized to an empty dictionary.

19.5. Template Imports

Objects can import attributes from other objects.


template Host "default-host" {
  vars.colour = "red"

template Host "test-host" {
  import "default-host"

  vars.colour = "blue"

object Host "localhost" {
  import "test-host"

  address = ""
  address6 = "::1"

The default-host and test-host objects are marked as templates using the template keyword. Unlike ordinary objects templates are not instantiated at run-time. Parent objects do not necessarily have to be templates, however in general they are.

The vars dictionary for the localhost object contains all three custom attributes and the custom attribute colour has the value "blue".

Parent objects are resolved in the order they're specified using the import keyword.

Default templates which are automatically imported into all object definitions can be specified using the default keyword:

template CheckCommand "plugin-check-command" default {
  // ...

Default templates are imported before any other user-specified statement in an object definition is evaluated.

If there are multiple default templates the order in which they are imported is unspecified.

19.6. Constants

Global constants can be set using the const keyword:

const VarName = "some value"

Once defined a constant can be accessed from any file. Constants cannot be changed once they are set.

Icinga 2 provides a number of special global constants. Some of them can be overridden using the --define command line parameter:

Variable Description
PrefixDir Read-only. Contains the installation prefix that was specified with cmake -DCMAKE_INSTALL_PREFIX. Defaults to "/usr/local".
SysconfDir Read-only. Contains the path of the sysconf directory. Defaults to PrefixDir + "/etc".
ZonesDir Read-only. Contains the path of the zones.d directory. Defaults to SysconfDir + "/zones.d".
LocalStateDir Read-only. Contains the path of the local state directory. Defaults to PrefixDir + "/var".
RunDir Read-only. Contains the path of the run directory. Defaults to LocalStateDir + "/run".
PkgDataDir Read-only. Contains the path of the package data directory. Defaults to PrefixDir + "/share/icinga2".
StatePath Read-write. Contains the path of the Icinga 2 state file. Defaults to LocalStateDir + "/lib/icinga2/icinga2.state".
ObjectsPath Read-write. Contains the path of the Icinga 2 objects file. Defaults to LocalStateDir + "/cache/icinga2/icinga2.debug".
PidPath Read-write. Contains the path of the Icinga 2 PID file. Defaults to RunDir + "/icinga2/icinga2.pid".
Vars Read-write. Contains a dictionary with global custom attributes. Not set by default.
NodeName Read-write. Contains the cluster node name. Set to the local hostname by default.
EventEngine Read-write. The name of the socket event engine, can be "poll" or "epoll". The epoll interface is only supported on Linux.
AttachDebugger Read-write. Whether to attach a debugger when Icinga 2 crashes. Defaults to false.
RunAsUser Read-write. Defines the user the Icinga 2 daemon is running as. Used in the init.conf configuration file.
RunAsGroup Read-write. Defines the group the Icinga 2 daemon is running as. Used in the init.conf configuration file.
PlatformName Read-only. The name of the operating system, e.g. "Ubuntu".
PlatformVersion Read-only. The version of the operating system, e.g. "14.04.3 LTS".
PlatformKernel Read-only. The name of the operating system kernel, e.g. "Linux".
PlatformKernelVersion Read-only. The version of the operating system kernel, e.g. "3.13.0-63-generic".
BuildCompilerName Read-only. The name of the compiler Icinga was built with, e.g. "Clang".
BuildCompilerVersion Read-only. The version of the compiler Icinga was built with, e.g. "".
BuildHostName Read-only. The name of the host Icinga was built on, e.g. "acheron".

19.7. Apply

The apply keyword can be used to create new objects which are associated with another group of objects.

apply Service "ping" to Host {
  import "generic-service"

  check_command = "ping4"

  assign where host.name == "localhost"

In this example the assign where condition is a boolean expression which is evaluated for all objects of type Host and a new service with name "ping" is created for each matching host. Expression operators may be used in assign where conditions.

The to keyword and the target type may be omitted if there is only one target type, e.g. for the Service type.

Depending on the object type used in the apply expression additional local variables may be available for use in the where condition:

Source Type Target Type Variables
Service Host host
Dependency Host host
Dependency Service host, service
Notification Host host
Notification Service host, service
ScheduledDowntime Host host
ScheduledDowntime Service host, service

Any valid config attribute can be accessed using the host and service variables. For example, host.address would return the value of the host's "address" attribute -- or null if that attribute isn't set.

More usage examples are documented in the monitoring basics chapter.

19.8. Apply For

Apply rules can be extended with the for loop keyword.

apply Service "prefix-" for (key => value in host.vars.dictionary) to Host {
  import "generic-service"

  check_command = "ping4"
  vars.host_value = value

Any valid config attribute can be accessed using the host and service variables. The attribute must be of the Array or Dictionary type. In this example host.vars.dictionary is of the Dictionary type which needs a key-value-pair as iterator.

In this example all generated service object names consist of prefix- and the value of the key iterator. The prefix string can be omitted if not required.

The key and value variables can be used for object attribute assignment, e.g. for setting the check_command attribute or custom attributes as command parameters.

apply for rules are first evaluated against all objects matching the for loop list and afterwards the assign where and ignore where conditions are evaluated.

It is not necessary to check attributes referenced in the for loop expression for their existance using an additional assign where condition.

More usage examples are documented in the monitoring basics chapter.

19.9. Group Assign

Group objects can be assigned to specific member objects using the assign where and ignore where conditions.

object HostGroup "linux-servers" {
  display_name = "Linux Servers"

  assign where host.vars.os == "Linux"

In this example the assign where condition is a boolean expression which is evaluated for all objects of the type Host. Each matching host is added as member to the host group with the name "linux-servers". Membership exclusion can be controlled using the ignore where condition. Expression operators may be used in assign where and ignore where conditions.

Source Type Variables
HostGroup host
ServiceGroup host, service
UserGroup user

19.10. Boolean Values

The assign where, ignore where, if and while statements, the ! operator as well as the bool() function convert their arguments to a boolean value based on the following rules:

Description Example Value Boolean Value
Empty value null false
Zero 0 false
Non-zero integer -23945 true
Empty string "" false
Non-empty string "Hello" true
Empty array [] false
Non-empty array [ "Hello" ] true
Empty dictionary {} false
Non-empty dictionary { key = "value" } true

For a list of supported expression operators for assign where and ignore where statements, see expression operators.


The Icinga 2 configuration format supports C/C++-style and shell-style comments.


 This is a comment.
object Host "localhost" {
  check_interval = 30 // this is also a comment.
  retry_interval = 15 # yet another comment

19.12. Includes

Other configuration files can be included using the include directive. Paths must be relative to the configuration file that contains the include directive.


include "some/other/file.conf"
include "conf.d/*.conf"

Wildcard includes are not recursive.

Icinga also supports include search paths similar to how they work in a C/C++ compiler:

include <itl>

Note the use of angle brackets instead of double quotes. This causes the config compiler to search the include search paths for the specified file. By default $PREFIX/share/icinga2/include is included in the list of search paths. Additional include search paths can be added using command-line options.

Wildcards are not permitted when using angle brackets.

19.13. Recursive Includes

The include_recursive directive can be used to recursively include all files in a directory which match a certain pattern.


include_recursive "conf.d", "*.conf"
include_recursive "templates"

The first parameter specifies the directory from which files should be recursively included.

The file names need to match the pattern given in the second parameter. When no pattern is specified the default pattern "*.conf" is used.

19.14. Zone Includes

The include_zones recursively includes all subdirectories for the given path.

In addition to that it sets the zone attribute for all objects created in these subdirectories to the name of the subdirectory.


include_zones "etc", "zones.d", "*.conf"
include_zones "puppet", "puppet-zones"

The first parameter specifies a tag name for this directive. Each include_zones invocation should use a unique tag name. When copying the zones' configuration files Icinga uses the tag name as the name for the destination directory in /var/lib/icinga2/api/config.

The second parameter specifies the directory which contains the subdirectories.

The file names need to match the pattern given in the third parameter. When no pattern is specified the default pattern "*.conf" is used.

19.15. Library directive

The library directive can be used to manually load additional libraries. Libraries can be used to provide additional object types and functions.


library "snmphelper"

19.16. Functions

Functions can be defined using the function keyword.


function multiply(a, b) {
  return a * b

When encountering the return keyword further execution of the function is terminated and the specified value is supplied to the caller of the function:

log(multiply(3, 5))

In this example the multiply function we declared earlier is invoked with two arguments (3 and 5). The function computes the product of those arguments and makes the result available to the function's caller.

When no value is supplied for the return statement the function returns null.

Functions which do not have a return statement have their return value set to the value of the last expression which was performed by the function. For example, we could have also written our multiply function like this:

function multiply(a, b) {
  a * b

Anonymous functions can be created by omitting the name in the function definition. The resulting function object can be used like any other value:

var fn = function() { 3 }

fn() /* Returns 3 */

19.17. Lambda Expressions

Functions can also be declared using the alternative lambda syntax.


f = (x) => x * x

Multiple statements can be used by putting the function body into braces:

f = (x) => {
  log("Lambda called")
  x * x

Just like with ordinary functions the return value is the value of the last statement.

For lambdas which take exactly one argument the braces around the arguments can be omitted:

f = x => x * x

19.18. Abbreviated Lambda Syntax

Lambdas which take no arguments can also be written using the abbreviated lambda syntax.


f = {{ 3 }}

This creates a new function which returns the value 3.

19.19. Variable Scopes

When setting a variable Icinga checks the following scopes in this order whether the variable already exists there:

  • Local Scope
  • this Scope
  • Global Scope

The local scope contains variables which only exist during the invocation of the current function, object or apply statement. Local variables can be declared using the var keyword:

function multiply(a, b) {
  var temp = a * b
  return temp

Each time the multiply function is invoked a new temp variable is used which is in no way related to previous invocations of the function.

When setting a variable which has not previously been declared as local using the var keyword the this scope is used.

The this scope refers to the current object which the function or object/apply statement operates on.

object Host "localhost" {
  check_interval = 5m

In this example the this scope refers to the "localhost" object. The check_interval attribute is set for this particular host.

You can explicitly access the this scope using the this keyword:

object Host "localhost" {
  var check_interval = 5m

  /* This explicitly specifies that the attribute should be set
   * for the host, if we had omitted `this.` the (poorly named)
   * local variable `check_interval` would have been modified instead.
  this.check_interval = 1m 


Similarly the keywords locals and globals are available to access the local and global scope.

Functions also have a this scope. However unlike for object/apply statements the this scope for a function is set to whichever object was used to invoke the function. Here's an example:

 hm = {
   h_word = null

   function init(word) {
     h_word = word

 /* Let's invoke the init() function */

We're using hm.init to invoke the function which causes the value of hm to become the this scope for this function call.

19.20. Closures

By default functions, objects and apply rules do not have access to variables declared outside of their scope (except for global variables).

In order to access variables which are defined in the outer scope the use keyword can be used:

function MakeHelloFunction(name) {
  return function() use(name) {
    log("Hello, " + name)

In this case a new variable name is created inside the inner function's scope which has the value of the name function argument.

Alternatively a different value for the inner variable can be specified:

function MakeHelloFunction(name) {
  return function() use (greeting = "Hello, " + name) {

19.21. Conditional Statements

Sometimes it can be desirable to only evaluate statements when certain conditions are met. The if/else construct can be used to accomplish this.


a = 3

if (a < 5) {
  a *= 7
} else if (a > 10) {
  a *= 5
} else {
  a *= 2

An if/else construct can also be used in place of any other value. The value of an if/else statement is the value of the last statement which was evaluated for the branch which was taken:

a = if (true) {
  log("Taking the 'true' branch")
  7 * 3
} else {
  log("Taking the 'false' branch")

This example prints the log message "Taking the 'true' branch" and the a variable is set to 21 (7 * 3).

The value of an if/else construct is null if the condition evaluates to false and no else branch is given.

19.22. While Loops

The while statement checks a condition and executes the loop body when the condition evaluates to true. This is repeated until the condition is no longer true.


var num = 5

while (num > 5) {
    num -= 1

The continue and break keywords can be used to control how the loop is executed: The continue keyword skips over the remaining expressions for the loop body and begins the next loop evaluation. The break keyword breaks out of the loop.

19.23. For Loops

The for statement can be used to iterate over arrays and dictionaries.


var list = [ "a", "b", "c" ]

for (item in list) {
  log("Item: " + item)

The loop body is evaluated once for each item in the array. The variable item is declared as a local variable just as if the var keyword had been used.

Iterating over dictionaries can be accomplished in a similar manner:

var dict = { a = 3, b = 7 }

for (key => value in dict) {
  log("Key: " + key + ", Value: " + value)

The continue and break keywords can be used to control how the loop is executed: The continue keyword skips over the remaining expressions for the loop body and begins the next loop evaluation. The break keyword breaks out of the loop.

19.24. Constructors

In order to create a new value of a specific type constructor calls may be used.


var pd = PerfdataValue()
pd.label = "test"
pd.value = 10

You can also try to convert an existing value to another type by specifying it as an argument for the constructor call.


var s = String(3) /* Sets s to "3". */

19.25. Exceptions

Built-in commands may throw exceptions to signal errors such as invalid arguments. User scripts can throw exceptions using the throw keyword.


throw "An error occurred."

There is currently no way for scripts to catch exceptions.

19.26. Breakpoints

The debugger keyword can be used to insert a breakpoint. It may be used at any place where an assignment would also be a valid expression.

By default breakpoints have no effect unless Icinga is started with the --script-debugger command-line option. When the script debugger is enabled Icinga stops execution of the script when it encounters a breakpoint and spawns a console which lets the user inspect the current state of the execution environment.

19.27. Types

All values have a static type. The typeof function can be used to determine the type of a value:

typeof(3) /* Returns an object which represents the type for numbers */

The following built-in types are available:

Type Examples Description
Number 3.7 A numerical value.
Boolean true, false A boolean value.
String "hello" A string.
Array [ "a", "b" ] An array.
Dictionary { a = 3 } A dictionary.

Depending on which libraries are loaded additional types may become available. The icinga library implements a whole bunch of other object types, e.g. Host, Service, CheckCommand, etc.

Each type has an associated type object which describes the type's semantics. These type objects are made available using global variables which match the type's name:

/* This logs 'true' */
log(typeof(3) == Number)

The type object's prototype property can be used to find out which methods a certain type supports:

/* This returns: ["contains","find","len","lower","replace","reverse","split","substr","to_string","trim","upper"] */

Additional documentation on type methods is available in the library reference.

19.28. Location Information

The location of the currently executing script can be obtained using the current_filename and current_line keywords.


log("Hello from '" + current_filename + "' in line " + current_line)

19.29. Reserved Keywords

These keywords are reserved and must not be used as constants or custom attributes.


You can escape reserved keywords using the @ character. The following example tries to set vars.include which references a reserved keyword and generates an error:

[2014-09-15 17:24:00 +0200] critical/config: Location:
/etc/icinga2/conf.d/hosts/localhost.conf(13):   vars.sla = "24x7"
/etc/icinga2/conf.d/hosts/localhost.conf(15):   vars.include = "some cmdb export field"
/etc/icinga2/conf.d/hosts/localhost.conf(16): }

Config error: in /etc/icinga2/conf.d/hosts/localhost.conf: 15:8-15:14: syntax error, unexpected include (T_INCLUDE), expecting T_IDENTIFIER
[2014-09-15 17:24:00 +0200] critical/config: 1 errors, 0 warnings.

You can escape the include keyword by prefixing it with an additional @ character:

object Host "localhost" {
  import "generic-host"

  address = ""
  address6 = "::1"

  vars.os = "Linux"
  vars.sla = "24x7"

  vars.@include = "some cmdb export field"