ctl_ohai.md

+++ title = "ohai (executable)" draft = false

gh_repo = "chef-web-docs"

aliases = ["/ctl_ohai.html"]

[menu] [menu.infra] title = "ohai (executable)" identifier = "chef_infra/features/ohai/ctl_ohai.md ohai Commands" parent = "chef_infra/features/ohai" weight = 20 +++

ohai is the command-line interface for Ohai, a tool that is used to detect attributes on a node, and then provide these attributes to Chef Infra Client at the start of every Chef Infra Client run.

Options

This command has the following syntax:

ohai OPTION

This tool has the following options:

ATTRIBUTE_NAME ATTRIBUTE NAME ...

: Use to have Ohai show only output for named attributes. To address attributes deeper in the tree, use a / delimiter between each level. For example: memory/free.

-c CONFIG, --config CONFIG

: The path to a configuration file to use. For example: /etc/ohai/config.rb.

-d DIRECTORY, --directory DIRECTORY

: The directory in which additional Ohai plugins are located. For example: /my/extra/plugins.

-h, --help

: Show help for the command.

-l LEVEL, --log_level LEVEL

: The level of logging to be stored in a log file.

-L LOGLOCATION, --logfile LOGLOCATION

: The location of the log file.

-v, --version

: The version of Ohai.

Examples

The following examples show how to use the Ohai command-line tool:

Query for a specific attribute

Pass an attribute as an argument to ohai to get the value of that attribute. For example:

ohai os

This fetches the value of Chef Infra's node data at node['os'] and returns something like:

[
  "linux"
]

To query for an attribute deeper in the tree, use a forward slash (/) as a delimiter. For example, to query for free memory, run:

ohai memory/free

Run a plugin independently of a Chef Infra Client run

An Ohai plugin can be run independently of a Chef Infra Client run. First, ensure that the plugin is located in the /plugins directory and then use the -f option when running Ohai from the command line. For example, a plugin named sl_installed may look like the following:

Ohai.plugin(:Sl) do
  provides "sl"

  collect_data(:default) do
    sl Mash.new

    if ::File.exist?("/usr/games/sl")
      sl[:installed] = true
    else
      sl[:installed] = false
    end

    # sl[:installed] = ::File.exist?("/usr/games/sl")

  end
end

To run that plugin from the command line, use the following command:

ohai --directory /path/to/directory sl

The command will return something similar to:

{
  "sl": {
    "installed": true
  }
}