execute

execute

Use the execute resource to execute a single command. Commands that are executed with this resource are (by their nature) not idempotent, as they are typically unique to the environment in which they are run. Use not_if and only_if to guard this resource for idempotence.

Syntax

A execute resource block typically executes a single command that is unique to the environment in which a recipe will run. Some execute resource commands are run by themselves, but often they are run in combination with other Chef resources. For example, a single command that is run by itself:

execute 'apache_configtest' do
  command '/usr/sbin/apachectl configtest'
end

where '/usr/sbin/apachectl configtest' is a command that tests if the configuration files for Apache are valid.

Commands are often run in combination with other Chef resources. The following example shows the template resource run with the execute resource to add an entry to a LDAP Directory Interchange Format (LDIF) file:

execute 'slapadd' do
  command 'slapadd < /tmp/something.ldif'
  creates '/var/lib/slapd/uid.bdb'
  action :nothing
end

template '/tmp/something.ldif' do
  source 'something.ldif'
  notifies :run, 'execute[slapadd]', :immediately
end

where

• '/tmp/something.ldif' specifies the location of the file
• 'something.ldif' specifies template file from which /tmp/something.ldif is created
• 'slapadd < /tmp/something.ldif' is the command that is run
• /var/lib/slapd/uid.bdb prevents the execute resource block from running if that file already exists

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

execute 'name' do
  command                    String, Array # defaults to 'name' if not specified
  creates                    String
  cwd                        String
  environment                Hash
  group                      String, Integer
  notifies                   # see description
  path                       Array
  provider                   Chef::Provider::Execute
  returns                    Integer, Array
  sensitive                  TrueClass, FalseClass
  subscribes                 # see description
  timeout                    Integer, Float
  umask                      String, Integer
  user                       String, Integer
  action                     Symbol # defaults to :run if not specified
end

where

• execute is the resource
• name is the name of the resource block
• command is the command to be run
• :action identifies the steps the chef-client will take to bring the node into the desired state
• command, creates, cwd, environment, group, path, provider, returns, sensitive, timeout, user, and umask 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.

execute 'bundle install' do
  cwd '/myapp'
  not_if 'bundle check' # This is not run inside /myapp
end

Actions

This resource has the following actions:

:nothing

Prevent a command from running. This action is used to specify that a command is run only when another resource notifies it.

:run

Default. Run a command.

Properties

This resource has the following properties:

command

Ruby Types: String, Array

The name of the command to be executed. Default value: the name of the resource block See “Syntax” section above for more information.

Note

Use the execute resource to run a single command. Use multiple execute resource blocks to run multiple commands.

creates

Ruby Type: String

Prevent a command from creating a file when that file already exists.

cwd

Ruby Type: String

The current working directory from which a command is run.

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.)

group

Ruby Types: String, Integer

The group name or group ID that must be changed before running a command.

ignore_failure

Ruby Types: TrueClass, FalseClass

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

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 notifiy 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:

: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

path

Ruby Type: Array

An array of paths to use when searching for a command. These paths are not added to the command’s environment $PATH. The default value uses the system path.

Warning

For example:

execute 'mycommand' do
  environment 'PATH' => "/my/path/to/bin:#{ENV['PATH']}"
end

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.

returns

Ruby Types: Integer, Array

The return value for a command. This may be an array of accepted values. An exception is raised when the return value(s) do not match. Default value: 0.

sensitive

Ruby Types: TrueClass, FalseClass

Ensure that sensitive resource data is not logged by the chef-client. Default value: false.

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.

A timer specifies the point during the chef-client run at which a notification is run. The following timers are available:

: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

timeout

Ruby Types: Integer, Float

The amount of time (in seconds) a command is to wait before timing out. Default value: 3600.

user

Ruby Types: String, Integer

The user name or user ID that should be changed before running a command.

umask

Ruby Types: String, Integer

The file mode creation mask, or umask.

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.

Attributes

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.

Arguments

The following arguments can be used with the not_if or only_if guard properties:

:user

Specify the user that a command will run as. For example:

not_if 'grep adam /etc/passwd', :user => 'adam'

:group

Specify the group that a command will run as. For example:

not_if 'grep adam /etc/passwd', :group => 'adam'

:environment

Specify a Hash of environment variables to be set. For example:

not_if 'grep adam /etc/passwd', :environment => {
  'HOME' => '/home/adam'
}

:cwd

Set the current working directory before running a command. For example:

not_if 'grep adam passwd', :cwd => '/etc'

:timeout

Set a timeout for a command. For example:

not_if 'sleep 10000', :timeout => 10

Providers

Where a resource represents a piece of the system (and its desired state), a provider defines the steps that are needed to bring that piece of the system from its current state into the desired state.

The chef-client will determine the correct provider based on configuration data collected by Ohai at the start of the chef-client run. This configuration data is then mapped to a platform and an associated list of providers.

Generally, it’s best to let the chef-client choose the provider, and this is (by far) the most common approach. However, in some cases, specifying a provider may be desirable. There are two approaches:

• Use a more specific short name—yum_package "foo" do instead of package "foo" do, script "foo" do instead of bash "foo" do, and so on—when available
• Use the provider property within the resource block to specify the long name of the provider as a property of a resource. For example: provider Chef::Provider::Long::Name

This resource has the following providers:

Chef::Provider::Execute, execute

The default provider for all platforms.

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.

Run a command upon notification

execute 'slapadd' do
  command 'slapadd < /tmp/something.ldif'
  creates '/var/lib/slapd/uid.bdb'
  action :nothing
end

template '/tmp/something.ldif' do
  source 'something.ldif'
  notifies :run, 'execute[slapadd]', :immediately
end

Run a touch file only once while running a command

execute 'upgrade script' do
  command 'php upgrade-application.php && touch /var/application/.upgraded'
  creates '/var/application/.upgraded'
  action :run
end

Run a command which requires an environment variable

execute 'slapadd' do
  command 'slapadd < /tmp/something.ldif'
  creates '/var/lib/slapd/uid.bdb'
  action :run
  environment ({'HOME' => '/home/myhome'})
end

Delete a repository using yum to scrub the cache

# the following code sample thanks to gaffneyc @ https://gist.github.com/918711

execute 'clean-yum-cache' do
  command 'yum clean all'
  action :nothing
end

file '/etc/yum.repos.d/bad.repo' do
  action :delete
  notifies :run, 'execute[clean-yum-cache]', :immediately
  notifies :create, 'ruby_block[reload-internal-yum-cache]', :immediately
end

Install repositories from a file, trigger a command, and force the internal cache to reload

The following example shows how to install new Yum repositories from a file, where the installation of the repository triggers a creation of the Yum cache that forces the internal cache for the chef-client to reload:

execute 'create-yum-cache' do
 command 'yum -q makecache'
 action :nothing
end

ruby_block 'reload-internal-yum-cache' do
  block do
    Chef::Provider::Package::Yum::YumCache.instance.reload
  end
  action :nothing
end

cookbook_file '/etc/yum.repos.d/custom.repo' do
  source 'custom'
  mode '0755'
  notifies :run, 'execute[create-yum-cache]', :immediately
  notifies :create, 'ruby_block[reload-internal-yum-cache]', :immediately
end

Prevent restart and reconfigure if configuration is broken

Use the :nothing action (common to all resources) to prevent an application from restarting, and then use the subscribes notification to ask the broken configuration to be reconfigured immediately:

execute 'test-nagios-config' do
  command 'nagios3 --verify-config'
  action :nothing
  subscribes :run, 'template[/etc/nagios3/configures-nagios.conf]', :immediately
end

Notify in a specific order

To notify multiple resources, and then have these resources run in a certain order, do something like the following:

execute 'foo' do
  command '...'
  notifies :create, 'template[baz]', :immediately
  notifies :install, 'package[bar]', :immediately
  notifies :run, 'execute[final]', :immediately
end

template 'baz' do
  ...
  notifies :run, 'execute[restart_baz]', :immediately
end

package 'bar'

execute 'restart_baz'

execute 'final' do
  command '...'
end

where the sequencing will be in the same order as the resources are listed in the recipe: execute 'foo', template 'baz', execute [restart_baz], package 'bar', and execute 'final'.

Execute a command using a template

The following example shows how to set up IPv4 packet forwarding using the execute resource to run a command named forward_ipv4 that uses a template defined by the template resource:

execute 'forward_ipv4' do
  command 'echo > /proc/.../ipv4/ip_forward'
  action :nothing
end

template '/etc/file_name.conf' do
  source 'routing/file_name.conf.erb'
  notifies :run, 'execute[forward_ipv4]', :delayed
end

where the command property for the execute resource contains the command that is to be run and the source property for the template resource specifies which template to use. The notifies property for the template specifies that the execute[forward_ipv4] (which is defined by the execute resource) should be queued up and run at the end of the chef-client run.

Add a rule to an IP table

The following example shows how to add a rule named test_rule to an IP table using the execute resource to run a command using a template that is defined by the template resource:

execute 'test_rule' do
  command 'command_to_run
    --option value
    ...
    --option value
    --source #{node[:name_of_node][:ipsec][:local][:subnet]}
    -j test_rule'
  action :nothing
end

template '/etc/file_name.local' do
  source 'routing/file_name.local.erb'
  notifies :run, 'execute[test_rule]', :delayed
end

where the command property for the execute resource contains the command that is to be run and the source property for the template resource specifies which template to use. The notifies property for the template specifies that the execute[test_rule] (which is defined by the execute resource) should be queued up and run at the end of the chef-client run.

Stop a service, do stuff, and then restart it

The following example shows how to use the execute, service, and mount resources together to ensure that a node running on Amazon EC2 is running MySQL. This example does the following:

• Checks to see if the Amazon EC2 node has MySQL
• If the node has MySQL, stops MySQL
• Installs MySQL
• Mounts the node
• Restarts MySQL

# the following code sample comes from the ``server_ec2``
# recipe in the following cookbook:
# https://github.com/chef-cookbooks/mysql

if (node.attribute?('ec2') && ! FileTest.directory?(node['mysql']['ec2_path']))

  service 'mysql' do
    action :stop
  end

  execute 'install-mysql' do
    command "mv #{node['mysql']['data_dir']} #{node['mysql']['ec2_path']}"
    not_if do FileTest.directory?(node['mysql']['ec2_path']) end
  end

  [node['mysql']['ec2_path'], node['mysql']['data_dir']].each do |dir|
    directory dir do
      owner 'mysql'
      group 'mysql'
    end
  end

  mount node['mysql']['data_dir'] do
    device node['mysql']['ec2_path']
    fstype 'none'
    options 'bind,rw'
    action [:mount, :enable]
  end

  service 'mysql' do
    action :start
  end

end

where

• the two service resources are used to stop, and then restart the MySQL service
• the execute resource is used to install MySQL
• the mount resource is used to mount the node and enable MySQL

Use the platform_family? method

The following is an example of using the platform_family? method in the Recipe DSL to create a variable that can be used with other resources in the same recipe. In this example, platform_family? is being used to ensure that a specific binary is used for a specific platform before using the remote_file resource to download a file from a remote location, and then using the execute resource to install that file by running a command.

if platform_family?('rhel')
  pip_binary = '/usr/bin/pip'
else
  pip_binary = '/usr/local/bin/pip'
end

remote_file "#{Chef::Config[:file_cache_path]}/distribute_setup.py" do
  source 'http://python-distribute.org/distribute_setup.py'
  mode '0755'
  not_if { File.exist?(pip_binary) }
end

execute 'install-pip' do
  cwd Chef::Config[:file_cache_path]
  command <<-EOF
    # command for installing Python goes here
    EOF
  not_if { File.exist?(pip_binary) }
end

where a command for installing Python might look something like:

#{node['python']['binary']} distribute_setup.py
#{::File.dirname(pip_binary)}/easy_install pip

Control a service using the execute resource

Do something like this:

service 'tomcat' do
  action :start
end

and NOT something like this:

execute 'start-tomcat' do
  command '/etc/init.d/tomcat6 start'
  action :run
end

There is no reason to use the execute resource to control a service because the service resource exposes the start_command property directly, which gives a recipe full control over the command issued in a much cleaner, more direct manner.

Use the search recipe DSL method to find users

The following example shows how to use the search method in the Recipe DSL to search for users:

#  the following code sample comes from the openvpn cookbook: https://github.com/chef-cookbooks/openvpn

search("users", "*:*") do |u|
  execute "generate-openvpn-#{u['id']}" do
    command "./pkitool #{u['id']}"
    cwd '/etc/openvpn/easy-rsa'
    environment(
      'EASY_RSA' => '/etc/openvpn/easy-rsa',
      'KEY_CONFIG' => '/etc/openvpn/easy-rsa/openssl.cnf',
      'KEY_DIR' => node['openvpn']['key_dir'],
      'CA_EXPIRE' => node['openvpn']['key']['ca_expire'].to_s,
      'KEY_EXPIRE' => node['openvpn']['key']['expire'].to_s,
      'KEY_SIZE' => node['openvpn']['key']['size'].to_s,
      'KEY_COUNTRY' => node['openvpn']['key']['country'],
      'KEY_PROVINCE' => node['openvpn']['key']['province'],
      'KEY_CITY' => node['openvpn']['key']['city'],
      'KEY_ORG' => node['openvpn']['key']['org'],
      'KEY_EMAIL' => node['openvpn']['key']['email']
    )
    not_if { File.exist?("#{node['openvpn']['key_dir']}/#{u['id']}.crt") }
  end

  %w{ conf ovpn }.each do |ext|
    template "#{node['openvpn']['key_dir']}/#{u['id']}.#{ext}" do
      source 'client.conf.erb'
      variables :username => u['id']
    end
  end

  execute "create-openvpn-tar-#{u['id']}" do
    cwd node['openvpn']['key_dir']
    command <<-EOH
      tar zcf #{u['id']}.tar.gz \
      ca.crt #{u['id']}.crt #{u['id']}.key \
      #{u['id']}.conf #{u['id']}.ovpn \
    EOH
    not_if { File.exist?("#{node['openvpn']['key_dir']}/#{u['id']}.tar.gz") }
  end
end

where

• the search will use both of the execute resources, unless the condition specified by the not_if commands are met
• the environments property in the first execute resource is being used to define values that appear as variables in the OpenVPN configuration
• the template resource tells the chef-client which template to use

Enable remote login for Mac OS X

execute 'enable ssh' do
  command '/usr/sbin/systemsetup -setremotelogin on'
  not_if '/usr/sbin/systemsetup -getremotelogin | /usr/bin/grep On'
  action :run
end

Execute code immediately, based on the template resource

By default, notifications are :delayed, that is they are queued up as they are triggered, and then executed at the very end of a chef-client run. To run an action immediately, use :immediately:

template '/etc/nagios3/configures-nagios.conf' do
  # other parameters
  notifies :run, 'execute[test-nagios-config]', :immediately
end

and then the chef-client would immediately run the following:

execute 'test-nagios-config' do
  command 'nagios3 --verify-config'
  action :nothing
end

Sourcing a file

The execute resource cannot be used to source a file (e.g. command 'source filename'). The following example will fail because source is not an executable:

execute 'foo' do
  command 'source /tmp/foo.sh'
end

Instead, use the script resource or one of the script-based resources (bash, csh, perl, python, or ruby). For example:

bash 'foo' do
  code 'source /tmp/foo.sh'
end

Run a Knife command

execute 'create_user' do
  command <<-EOM.gsub(/\s+/, ' ').strip!
        knife user create #{user}
      --admin
      --password password
      --disable-editing
      --file /home/vagrant/.chef/user.pem
      --config /tmp/knife-admin.rb
    EOM
end

Run install command into virtual environment

The following example shows how to install a lightweight JavaScript framework into Vagrant:

execute "install q and zombiejs" do
  cwd "/home/vagrant"
  user "vagrant"
  environment ({'HOME' => '/home/vagrant', 'USER' => 'vagrant'})
  command "npm install -g q zombie should mocha coffee-script"
  action :run
end

Run a command as a named user

The following example shows how to run bundle install from a chef-client run as a specific user. This will put the gem into the path of the user (vagrant) instead of the root user (under which the chef-client runs):

execute '/opt/chefdk/embedded/bin/bundle install' do
  cwd node['chef_workstation']['bundler_path']
  user node['chef_workstation']['user']
  environment ({
    'HOME' => "/home/#{node['chef_workstation']['user']}",
    'USER' => node['chef_workstation']['user']
  })
  not_if 'bundle check'
end