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sysctl resource

Resources Reference page


Use the sysctl resource to set or remove kernel parameters using the sysctl command line tool and configuration files in the system’s sysctl.d directory. Configuration files managed by this resource are named 99-chef-KEYNAME.conf. If an existing value was already set, it will be backed up to the node and restored if the :remove action is used later.

New in Chef Infra Client 14.0.

Syntax


The full syntax for all of the properties that are available to the sysctl resource is:

sysctl 'name' do
  comment           Array, String # default value: []
  conf_dir          String # default value: "/etc/sysctl.d"
  ignore_error      true, false # default value: false
  key               String # default value: 'name' unless specified
  value             Array, String, Integer, Float
  action            Symbol # defaults to :apply if not specified
end

where:

  • sysctl is the resource.
  • name is the name given to the resource block.
  • action identifies which steps Chef Infra Client will take to bring the node into the desired state.
  • comment, conf_dir, ignore_error, key, and value are the properties available to this resource.

Actions


The sysctl resource has the following actions:

:apply
Default. Set the kernel parameter and update the sysctl settings.
:nothing
This resource block does not act unless notified by another resource to take action. Once notified, this resource block either runs immediately or is queued up to run at the end of a Chef Infra Client run.
:remove
Remove the kernel parameter and update the sysctl settings.

Properties


The sysctl resource has the following properties:

comment
Ruby Type: Array, String | Default Value: []

Comments, placed above the resource setting in the generated file. For multi-line comments, use an array of strings, one per line.

New in Chef Infra Client 15.8

conf_dir
Ruby Type: String | Default Value: /etc/sysctl.d

The configuration directory to write the config to.

ignore_error
Ruby Type: true, false | Default Value: false

Ignore any errors when setting the value on the command line.

key
Ruby Type: String | Default Value: The resource block's name

The kernel parameter key in dotted format if it differs from the resource block’s name.

value
Ruby Type: Array, String, Integer, Float | REQUIRED

The value to set.


Common Resource Functionality


Chef resources include common properties, notifications, and resource guards.

Common Properties

The following properties are common to every resource:

ignore_failure

Ruby Type: true, false | Default Value: false

Continue running a recipe if a resource fails for any reason.

retries

Ruby Type: Integer | Default Value: 0

The number of attempts to catch exceptions and retry the resource.

retry_delay

Ruby Type: Integer | Default Value: 2

The retry delay (in seconds).

sensitive

Ruby Type: true, false | Default Value: false

Ensure that sensitive resource data is not logged by Chef Infra Client.

Notifications

notifies

Ruby Type: Symbol, 'Chef::Resource[String]'

A resource may notify another resource to take action when its state changes. Specify a 'resource[name]', the :action that resource should take, and then the :timer for that action. A resource may notify more than one resource; use a notifies statement for each resource to be notified.

A timer specifies the point during a Chef Infra Client run at which a notification is run. The following timers are available:

:before

Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.

:delayed

Default. Specifies that a notification should be queued up, and then executed at the end of a Chef Infra Client run.

:immediate, :immediately

Specifies that a notification should be run immediately, per resource notified.

The syntax for notifies is:

notifies :action, 'resource[name]', :timer
subscribes

Ruby Type: Symbol, 'Chef::Resource[String]'

A resource may listen to another resource, and then take action if the state of the resource being listened to changes. Specify a 'resource[name]', the :action to be taken, and then the :timer for that action.

Note that subscribes does not apply the specified action to the resource that it listens to - for example:

file '/etc/nginx/ssl/example.crt' do
  mode '0600'
  owner 'root'
end

service 'nginx' do
  subscribes :reload, 'file[/etc/nginx/ssl/example.crt]', :immediately
end

In this case the subscribes property reloads the nginx service whenever its certificate file, located under /etc/nginx/ssl/example.crt, is updated. subscribes does not make any changes to the certificate file itself, it merely listens for a change to the file, and executes the :reload action for its resource (in this example nginx) when a change is detected.

A timer specifies the point during a Chef Infra Client run at which a notification is run. The following timers are available:

:before

Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.

:delayed

Default. Specifies that a notification should be queued up, and then executed at the end of a Chef Infra Client run.

:immediate, :immediately

Specifies that a notification should be run immediately, per resource notified.

The syntax for subscribes is:

subscribes :action, 'resource[name]', :timer

Guards

A guard property can be used to evaluate the state of a node during the execution phase of a Chef Infra Client run. Based on the results of this evaluation, a guard property is then used to tell Chef Infra Client if it should continue executing a resource. A guard property accepts either a string value or a Ruby block value:

  • A string is executed as a shell command. If the command returns 0, the guard is applied. If the command returns any other value, then the guard property is not applied. String guards in a powershell_script run Windows PowerShell commands and may return true in addition to 0.
  • A block is executed as Ruby code that must return either true or false. If the block returns true, the guard property is applied. If the block returns false, the guard property is not applied.

A guard property is useful for ensuring that a resource is idempotent by allowing that resource to test for the desired state as it is being executed, and then if the desired state is present, for Chef Infra Client to do nothing.

Properties

The following properties can be used to define a guard that is evaluated during the execution phase of a Chef Infra Client run:

not_if

Prevent a resource from executing when the condition returns true.

only_if

Allow a resource to execute only if the condition returns true.

Examples


The following examples demonstrate various approaches for using the sysctl resource in recipes:

Set vm.swappiness:

sysctl 'vm.swappiness' do
  value 19
end

Remove kernel.msgmax:

Note: This only removes the sysctl.d config for kernel.msgmax. The value will be set back to the kernel default value.

sysctl 'kernel.msgmax' do
  action :remove
end

Adding Comments to sysctl configuration files:

sysctl 'vm.swappiness' do
  value 19
  comment "define how aggressively the kernel will swap memory pages."
end

This produces /etc/sysctl.d/99-chef-vm.swappiness.conf as follows:

# define how aggressively the kernel will swap memory pages.
vm.swappiness = 1

Converting sysctl settings from shell scripts:

Example of existing settings:

fs.aio-max-nr = 1048576 net.ipv4.ip_local_port_range = 9000 65500 kernel.sem = 250 32000 100 128

Converted to sysctl resources:

sysctl 'fs.aio-max-nr' do
  value '1048576'
end

sysctl 'net.ipv4.ip_local_port_range' do
  value '9000 65500'
end

sysctl 'kernel.sem' do
  value '250 32000 100 128'
end