What is Ohai and How to use Ohai in Chef server?

• It is a system discovery tool.
• It gathers system information.

• ohai 

• Now run

• ohai ipaddress
• ohai hostname
• ohai memory/total
• ohai cpu/0/mhz  

Attributes

• We have a web application to be deployed into 1000 nodes & we need to know some
details of each server.
• Because we need to mention that in the configuration file of each node. This information varies from system to system.
• These details we call “Attributes”
• chef-client tool gathers these Attributes from the ohai store and puts them in configuration files.
• Instead of hard coding these attributes, we mention them as variables.

file '/robofile' do
content "This is to get Attributes
HOSTNAME: #{node['hostname']}
IPADDRESS: #{node['ipaddress']}
CPU: #{node['cpu']['0']['mhz']}
MEMORY: #{node['memory']['total']}"
owner 'root'
group 'root'
action :create
end

Execute

• To execute Linux commands

execute “run a script” do
 command <<-EOH
 mkdir /saidir
 touch /saifile
 EOH
end

User & Group

• We can create users & Groups

Users

user “raj” do
   action :create
end

Verify : cat /etc/passwd

Group

group “devops” do
 action :create
 members ‘raj’
 append true
end

Verify : cat /etc/group