apt_preference resource¶

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The apt_preference resource allows for the creation of APT preference files. Preference files are used to control which package versions and sources are prioritized during installation.

New in Chef Client 13.3.

Syntax¶

The apt_preference resource has the following syntax:

apt_preference 'name' do
  glob              String
  package_name      String # default value: 'name' unless specified
  pin               String
  pin_priority      String, Integer
  action            Symbol # defaults to :add if not specified
end

where:

apt_preference 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.
glob, package_name, pin, and pin_priority are the properties available to this resource.

Actions¶

The apt_preference resource has the following actions:

add: Default action. Creates a preferences file under /etc/apt/preferences.d.
remove: Removes the preferences file, thus unpinning the package.
: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.

Properties¶

The apt_preference resource has the following properties:

glob

Ruby Type: String

Pin by glob() expression or with regular expressions surrounded by /.

package_name

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

An optional property to set the package name if it differs from the resource block’s name.

pin

Ruby Type: String | REQUIRED

The package version or repository to pin.

pin_priority

Ruby Type: String, Integer | REQUIRED

Sets the Pin-Priority for a package. See the APT pinning documentation for more details.

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 resources in recipes:

Pin a package to a specific version

This example pins the libmysqlclient16 package to version 5.1.49-3:

apt_preference 'libmysqlclient16' do
  pin          'version 5.1.49-3'
  pin_priority '700'
end

Note that the pin_priority of 700 ensures that this version will be preferred over any other available versions.

Unpin a package

This example unpins the libmysqlclient16 package, disabling all preferences for it:

apt_preference 'libmysqlclient16' do
  action :remove
end

Pin all packages to prefer a specific repository

This example instructs APT to prefer the packages.dotdeb.org repository:

apt_preference 'dotdeb' do
  glob         '*'
  pin          'origin packages.dotdeb.org'
  pin_priority '700'
end