Deep dive into Ansible ad hoc commands

Automation plays a vital role in a sysadmin's or DevOps administrator's day-to-day life; patching, installing, managing components, automating network devices, and dealing with containers are tasks that automation can handle. Due to the sequential behavior of scripting, many sysadmins have not considered automation to be a promising tool. Ansible, as an automation tool that executes in parallel, appears to be changing that trend and becoming widely used.

Ansible uses ad hoc commands and playbooks to achieve automation. Ad hoc commands are mostly single linear commands that can execute from controllers. Ad hoc commands make Ansible useful even when a sysadmin needs to perform a one-time activity.

This article examines different aspects and options available in Ansible ad hoc commands such as --limit, -B, -a, -m, and -b.

Consideration: Inventory details are mentioned in the myinventory file, as shown here:

cat myinventory
[app]
localhost
172.6.7.8
172.6.7.80

[multi]
172.6.7.4
172.6.7.10
172.6.7.8

A few examples of ad hoc commands are included in this line of code:

$ ansible app -b -m yum -a "name=MySQL-python state=present"

These commands install a MySQL-python package on the app group. The -b option runs an operation with become. You can provide the username using –become-user. The -m option specifies modules such as: copy, user, yum, and more. The -a option is an attribute of a specific module.

Here is another example, which executes only on the IP address specified (172.6.7.10):

$ ansible app -b -a "systemctl status ntpd" --limit "172.6.7.10"

The --limit option limits the selected hosts to a different pattern, and you can also use wildcards like *, !, and & (as shown in the examples below).

The first example command below executes the ad hoc command on any node that ends with a .4 IP address. The second example executes on an app group on the IP 172.6.7.80. The last example executes on any machine from both groups. In this case, 172.6.7.8 is present in both groups.

$ ansible app -b -a "systemctl status ntpd" --limit "*.4"

$ ansible app -b -a "systemctl status ntpd" --limit "app:!172.6.7.80”

$ ansible app -b -a "systemctl status ntpd" --limit "app:&multi”

Ad hoc commands can also be used with the user, stat, copy, and file modules:

$ ansible app -s -m user -a "name=admin state=present"

$ ansible multi -m stat -a "path=/etc/environment"

$ ansible multi -m copy -a "src=/etc/hosts dest=/tmp/hosts"

$ ansible multi -m file -a "dest=/tmp/test mode=644 state=directory"

In some cases, an Ansible ad hoc command may take a while to execute because it needs to wait for a long time. Using the -B option, you can easily schedule the commands in the background:

$ ansible multi -b -B 3600 -a "yum -y update"

Managed-host logging is easy to achieve using the tail/tailf commands:

$ ansible multi -b -a "tail /var/log/messages"

[ Need more on Ansible? Take a free technical overview course from Red Hat. Ansible Essentials: Simplicity in Automation Technical Overview. ]

Wrapping up

Using ad hoc commands, a sysadmin can verify the desired state of a particular task before and after execution. The options in this article may make life easier while dealing with Ansible automation.