ohai¶
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
subscribes # see description
action Symbol # defaults to :reload if not specified
end
where
ohai
is the resourcename
is the name of the resource blockaction
identifies the steps the chef-client will take to bring the node into the desired statename
andplugin
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: True, False
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 anotifies
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.
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 thenginx
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 examplenginx
) 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