Verifying the Ansible installation

In this section, you will learn how you can verify your Ansible installation with simple ad hoc commands.

To ensure Ansible can authenticate with your private key, you could make use of ssh-agent—the commands show a simple example of how to start ssh-agent and add your private key to it. Naturally, you should replace the path with that to your own private key:

$ ssh-agent bash 
$ ssh-add ~/.ssh/id_rsa

[frontends]
frt01.example.com
frt02.example.com

The ansible command that we used in the previous section has two important switches that you will almost always use: -m <MODULE_NAME> to run a module on the hosts from your inventory that you specify and, optionally, the module arguments passed using the -a OPT_ARGS switch. Commands run using the ansible binary are known as ad hoc commands.

Following are three simple examples that demonstrate ad hoc commands—they are also valuable for verifying both the installation of Ansible on your control machine and the configuration of your target hosts, and they will return an error if there is an issue with any part of the configuration:

• Ping hosts: You can perform an Ansible "ping" on your inventory hosts using the following command:

$ ansible frontends -i hosts -m ping

• Display gathered facts: You can display gathered facts about your inventory hosts using the following command:

$ ansible frontends -i hosts -m setup | less

• Filter gathered facts: You can filter gathered facts using the following command:

$ ansible frontends -i hosts -m setup -a "filter=ansible_distribution*"

For every ad hoc command you run, you will get a response in JSON format—the following example output results from running the ping module successfully: 

$ ansible frontends -m ping 
frontend01.example.com | SUCCESS => {
    "changed": false, 
    "ping": "pong"
}
frontend02.example.com | SUCCESS => {
    "changed": false, 
    "ping": "pong"
}

$ ansible frontend01.example.com -m setup -a "filter=ansible_distribution*"
frontend01.example.com | SUCCESS => {
 ansible_facts": {
 "ansible_distribution": "macOS", 
 "ansible_distribution_major_version": "10", 
 "ansible_distribution_release": "18.5.0", 
 "ansible_distribution_version": "10.14.4"
 }, 
 "changed": false

Ad hoc commands are incredibly powerful, both for verifying your Ansible installation and for learning Ansible and how to work with modules as you don't need to write a whole playbook—you can just run a module with an ad hoc command and learn how it responds. Here are some more ad hoc examples for you to consider:

• Copy a file from the Ansible control host to all hosts in the frontends group with the following command:

$ ansible frontends -m copy -a "src=/etc/yum.conf dest=/tmp/yum.conf"

• Create a new directory on all hosts in the frontends inventory group, and create it with specific ownership and permissions:

$ ansible frontends -m file -a "dest=/path/user1/new mode=777 owner=user1 group=user1 state=directory" 

• Delete a specific directory from all hosts in the frontends group with the following command:

$ ansible frontends -m file -a "dest=/path/user1/new state=absent"

• Install the httpd package with yum if it is not already present—if it is present, do not update it. Again, this applies to all hosts in the frontends inventory group:

$ ansible frontends -m yum -a "name=httpd state=present"

• The following command is similar to the previous one, except that changing state=present to state=latest causes Ansible to install the (latest version of the) package if it is not present, and update it to the latest version if it is present:

$ ansible frontends -m yum -a "name=demo-tomcat-1 state=latest" 

• Display all facts about all the hosts in your inventory (warning—this will produce a lot of JSON!):

$ ansible all -m setup 

Now that you have learned more about verifying your Ansible installation and about how to run ad hoc commands, let's proceed to look in a bit more detail at the requirements of the nodes that are to be managed by Ansible.