knife exec

The knife exec subcommand uses the knife configuration file to execute Ruby scripts in the context of a fully configured chef-client. This subcommand is most often used to run scripts that will only access Chef server one time (or otherwise very infrequently). Use this subcommand any time that an operation does not warrant full usage of the knife subcommand library.

Authenticated API Requests

The knife exec subcommand can be used to make authenticated API requests to the Chef server using the following methods:

Method	Description
api.delete	Use to delete an object from the Chef server.
api.get	Use to get the details of an object on the Chef server.
api.post	Use to add an object to the Chef server.
api.put	Use to update an object on the Chef server.

These methods are used with the -E option, which executes that string locally on the workstation using chef-shell. These methods have the following syntax:

$ knife exec -E 'api.method(/endpoint)'

where:

• api.method is the corresponding authentication method — api.delete, api.get, api.post, or api.put
• /endpoint is an endpoint in the Chef server API

For example, to get the data for a node named “Example_Node”:

$ knife exec -E 'puts api.get("/nodes/Example_Node")'

and to ensure that the output is visible in the console, add the puts in front of the API authorization request:

$ knife exec -E 'puts api.get("/nodes/Example_Node")'

where puts is the shorter version of the $stdout.puts predefined variable in Ruby.

The following example shows how to add a client named “IBM305RAMAC” and the /clients endpoint, and then return the private key for that user in the console:

$ client_desc = {
    "name"  => "IBM305RAMAC",
    "admin" => false
  }

  new_client = api.post("/clients", client_desc)
  puts new_client["private_key"]

Ruby Scripts

For Ruby scripts that will be run using the exec subcommand, note the following:

• The Ruby script must be located on the system from which knife is run (and not be located on any of the systems that knife will be managing).
• Shell commands will be run from a management workstation. For example, something like %x[ls -lash /opt/only-on-a-node] would give you the directory listing for the “opt/only-on-a-node” directory or a “No such file or directory” error if the file does not already exist locally.
• When the chef-shell DSL is available, the chef-client DSL will not be (unless the management workstation is also a chef-client). Without the chef-client DSL, a bash block cannot be used to run bash commands.

Syntax

This subcommand has the following syntax:

$ knife exec SCRIPT (options)

Options

Note

Review the list of common options available to this (and all) knife subcommands and plugins.

This subcommand has the following options:

-E CODE, --exec CODE

A string of code that will be executed.

-p PATH:PATH, --script-path PATH:PATH

A colon-separated path at which Ruby scripts are located. Use to override the default location for scripts. When this option is not specified, knife will look for scripts located in chef-repo/.chef/scripts directory.

Examples

The following examples show how to use this knife subcommand:

Run Ruby scripts

There are three ways to use knife exec to run Ruby script files. For example:

$ knife exec /path/to/script_file

or:

$ knife exec -E 'RUBY CODE'

or:

$ knife exec
RUBY CODE
^D

Chef Knife status

To check the status of knife using a Ruby script named status.rb (which looks like):

printf "%-5s %-12s %-8s %s\n", "Check In", "Name", "Ruby", "Recipes"
nodes.all do |n|
   checkin = Time.at(n['ohai_time']).strftime("%F %R")
   rubyver = n['languages']['ruby']['version']
   recipes = n.run_list.expand(_default).recipes.join(", ")
   printf "%-20s %-12s %-8s %s\n", checkin, n.name, rubyver, recipes
end

and is located in a directory named scripts/, enter:

$ knife exec scripts/status.rb

List available free memory

To show the available free memory for all nodes, enter:

$ knife exec -E 'nodes.all {|n| puts "#{n.name} has #{n.memory.total} free memory"}'

List available search indexes

To list all of the available search indexes, enter:

$ knife exec -E 'puts api.get("search").keys'

Query for multiple attributes

To query a node for multiple attributes using a Ruby script named search_attributes.rb (which looks like):

% cat scripts/search_attributes.rb
query = ARGV[2]
attributes = ARGV[3].split(",")
puts "Your query: #{query}"
puts "Your attributes: #{attributes.join(" ")}"
results = {}
search(:node, query) do |n|
   results[n.name] = {}
   attributes.each {|a| results[n.name][a] = n[a]}
end

puts results
exit 0

enter:

% knife exec scripts/search_attributes.rb "hostname:test_system" ipaddress,fqdn

to return something like:

Your query: hostname:test_system
Your attributes: ipaddress fqdn
{"test_system.example.com"=>{"ipaddress"=>"10.1.1.200", "fqdn"=>"test_system.example.com"}}