cron resource

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Use the cron resource to manage cron entries for time-based job scheduling.

Warning

The cron resource should only be used to modify an entry in a crontab file. The cron_d resource directly manages cron.d files. This resource ships in Chef 14.4 or later and can also be found in the cron cookbook) for previous chef-client releases.

Syntax

A cron resource block manages cron entries. For example, to get a weekly cookbook report from the Chef Supermarket:

cron 'cookbooks_report' do
  action :create
  minute '0'
  hour '0'
  weekday '1'
  user 'getchef'
  mailto 'sysadmin@example.com'
  home '/srv/supermarket/shared/system'
  command %W{
    cd /srv/supermarket/current &&
    env RUBYLIB="/srv/supermarket/current/lib"
    RAILS_ASSET_ID=`git rev-parse HEAD` RAILS_ENV="#{rails_env}"
    bundle exec rake cookbooks_report
  }.join(' ')
end

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

cron 'name' do
  command          String
  day
  environment      Hash
  home             String
  hour
  mailto           String
  minute
  month
  path             String
  shell            String
  time             Symbol
  user             String # default value: "root"
  weekday
  action           Symbol # defaults to :create if not specified
end

where:

  • cron is the resource.
  • name is the name given to the resource block.
  • action identifies which steps the chef-client will take to bring the node into the desired state.
  • command, day, environment, home, hour, mailto, minute, month, path, shell, time, user, and weekday are the properties available to this resource.

Actions

The cron resource has the following actions:

:create
Default. Create an entry in a cron table file (crontab). If an entry already exists (but does not match), update that entry to match.
:delete
Delete an entry from a cron table file (crontab).
: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 the Chef Client run.

Note

Chef can only reliably manage crontab entries that it creates. To remove existing system entries we may use execute resource with a guard like:

execute "remove foo_daemon from crontab" do
  command "sed -i '/foo_daemon/d' /etc/crontab"
  only_if "grep 'foo_daemon' /etc/crontab 2>&1 >/dev/null"
end

Properties

The cron resource has the following properties:

command

Ruby Type: String

The command to be run, or the path to a file that contains the command to be run.

Some examples:

command if [ -x /usr/share/mdadm/checkarray ] && [ $(date +\%d) -le 7 ];
then /usr/share/mdadm/checkarray --cron --all --idle --quiet; fi

and:

command %w{
  cd /srv/opscode-community-site/current &&
  env RUBYLIB="/srv/opscode-community-site/current/lib"
  RAILS_ASSET_ID=`git rev-parse HEAD` RAILS_ENV="#{rails_env}"
  bundle exec rake cookbooks_report
}.join(' ')

and:

command "/srv/app/scripts/daily_report"
day

Ruby Type: String | Default Value: *

The day of month at which the cron entry should run (1 - 31).

environment

Ruby Type: Hash

A Hash of environment variables in the form of ({'ENV_VARIABLE' => 'VALUE'}). (These variables must exist for a command to be run successfully.)

home

Ruby Type: String

Set the HOME environment variable.

hour

Ruby Type: String | Default Value: *

The hour at which the cron entry is to run (0 - 23).

mailto

Ruby Type: String

Set the MAILTO environment variable.

minute

Ruby Type: String | Default Value: *

The minute at which the cron entry should run (0 - 59).

month

Ruby Type: String | Default Value: *

The month in the year on which a cron entry is to run (1 - 12).

path

Ruby Type: String

Set the PATH environment variable.

shell

Ruby Type: String

Set the SHELL environment variable.

time

Ruby Type: Symbol

A time interval. Possible values: :annually, :daily, :hourly, :midnight, :monthly, :reboot, :weekly, or :yearly.

user

Ruby Type: String | Default Value: "root"

The name of the user that runs the command. If the user property is changed, the original user for the crontab program continues to run until that crontab program is deleted. This property is not applicable on the AIX platform.

weekday

Ruby Type: String | Default Value: *

The day of the week on which this entry is to run (0 - 6), where Sunday = 0.

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 the chef-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 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 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
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 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

Guards

A guard property can be used to evaluate the state of a node during the execution phase of the chef-client run. Based on the results of this evaluation, a guard property is then used to tell the chef-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 the chef-client to do nothing.

The following properties can be used to define a guard that is evaluated during the execution phase of the chef-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:

Run a program at a specified interval

cron 'noop' do
  hour '5'
  minute '0'
  command '/bin/true'
end

Run an entry if a folder exists

cron 'ganglia_tomcat_thread_max' do
  command "/usr/bin/gmetric
    -n 'tomcat threads max'
    -t uint32
    -v '/usr/local/bin/tomcat-stat
    --thread-max'"
  only_if do File.exist?('/home/jboss') end
end

Run every Saturday, 8:00 AM

The following example shows a schedule that will run every hour at 8:00 each Saturday morning, and will then send an email to “admin@example.com” after each run.

cron 'name_of_cron_entry' do
  minute '0'
  hour '8'
  weekday '6'
  mailto 'admin@example.com'
  action :create
end

Run only in November

The following example shows a schedule that will run at 8:00 PM, every weekday (Monday through Friday), but only in November:

cron 'name_of_cron_entry' do
  minute '0'
  hour '20'
  day '*'
  month '11'
  weekday '1-5'
  action :create
end