ohai

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Use the ohai resource to reload the Ohai configuration on a node. This allows recipes that change system attributes (like a recipe that adds a user) to refer to those attributes later on during the chef-client run.

Syntax

A ohai resource block reloads the Ohai configuration on a node:

ohai 'reload' do
  action :reload
end

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

ohai 'name' do
  name                       String
  notifies                   # see description
  plugin                     String
  provider                   Chef::Provider::Ohai
  subscribes                 # see description
  action                     Symbol # defaults to :reload if not specified
end

where

  • ohai is the resource
  • name is the name of the resource block
  • action identifies the steps the chef-client will take to bring the node into the desired state
  • name, plugin, and provider are properties of this resource, with the Ruby type shown. See “Properties” section below for more information about all of the properties that may be used with this resource.

Actions

This resource has the following actions:

:nothing
Define this resource block to do nothing until notified by another resource to take action. When this resource is notified, this resource block is either run immediately or it is queued up to be run at the end of the chef-client run.
:reload
Default. Reload the Ohai configuration on a node.

Properties

This resource has the following properties:

ignore_failure

Ruby Types: TrueClass, FalseClass

Continue running a recipe if a resource fails for any reason. Default value: false.

name

Ruby Type: String

Always the same value as the name of the resource block. See “Syntax” section above for more information.

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 the chef-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 very end of the chef-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
plugin

Ruby Type: String

Optional. The name of an Ohai plugin to be reloaded. If this property is not specified, the chef-client will reload all plugins.

provider

Ruby Type: Chef Class

Optional. Explicitly specifies a provider.

retries

Ruby Type: Integer

The number of times to catch exceptions and retry the resource. Default value: 0.

retry_delay

Ruby Type: Integer

The retry delay (in seconds). Default value: 2.

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 the chef-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 very end of the chef-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

Examples

The following examples demonstrate various approaches for using resources in recipes. If you want to see examples of how Chef uses resources in recipes, take a closer look at the cookbooks that Chef authors and maintains: https://github.com/chef-cookbooks.

Reload Ohai

ohai 'reload' do
  action :reload
end

Reload Ohai after a new user is created

ohai 'reload_passwd' do
  action :nothing
  plugin 'etc'
end

user 'daemonuser' do
  home '/dev/null'
  shell '/sbin/nologin'
  system true
  notifies :reload, 'ohai[reload_passwd]', :immediately
end

ruby_block 'just an example' do
  block do
    # These variables will now have the new values
    puts node['etc']['passwd']['daemonuser']['uid']
    puts node['etc']['passwd']['daemonuser']['gid']
  end
end