Ansible Ad-hoc Commands Guide

What are Ad-hoc Commands?

Ad-Hoc commands are quick, "one-liner" tasks used to perform a single action on multiple managed nodes without writing a full Playbook. They are great for quick checks, updates, or reboots.

Basic Syntax:

ansible [group/host] -m [module] -a "[arguments]" -b

Key Flags Breakdown

• -m [module]: Defines which module to run (e.g., ping, yum, service). If omitted, it defaults to command.

• -a "[options]": Provides arguments to the module (e.g., package name, service state).

• -b (Become): Runs the command with sudo privileges (essential for installing packages or changing system files).

• -i [inventory]: Specifies the inventory file path (optional if defined in ansible.cfg).

Connectivity & System Information

Ping All Hosts

Checks if Ansible can connect to the hosts via SSH and find the Python interpreter.

ansible all -m ping

• Why important?: First step to verify your inventory and keys are working.

Check System Uptime

ansible all -m command -a "uptime"

• Module command: The default module. It runs simple commands but doesn't support variables like $HOME or operations like | (pipe) or >.

Gather Facts (system Details)

Collects detailed info (IP, OS version, CPU, Memory) about remote hosts.

ansible all -m setup

Filter Specific Facts: To see only specific info (e.g., only IP addresses):

ansible all -m setup -a "filter=ansible_default_ipv4.address"

• Argument filter: Limits the massive output to just what you need.

Package Management (yum/dnf/apt)

Install a Package

Installs Nginx using the yum module.

ansible all -m yum -a "name=nginx state=present" -b

• name=nginx: The package name.

• state=present: Ensures the package is installed. (Use state=latest to update it).

• -b: Crucial. You cannot install packages without root/sudo access.

Remove a Package

ansible all -m yum -a "name=httpd state=absent" -b

• state=absent: The standard Ansible way to say "Uninstall" or "Delete".

Upgrade All Packages

ansible all -m yum -a "name=* state=latest" -b

• name=*: Selects all packages.

• state=latest: Updates them to the newest version available.

Service Management

Start & Enable a Service

Starts Nginx and ensures it runs on boot.

ansible all -m service -a "name=nginx state=started enabled=yes" -b

• state=started: Starts the service if it's stopped.

• enabled=yes: Runs systemctl enable, checking the service starts after reboot.

Restart a Service

Useful after configuration changes.

ansible all -m service -a "name=nginx state=restarted" -b

Stop a Service

ansible all -m service -a "name=nginx state=stopped" -b

File & Directory Management

Create a Directory

ansible all -m file -a "path=/tmp/testdir state=directory mode=0755"

• state=directory: Tells Ansible to create a folder, not a file.

• mode=0755: Sets Linux permissions (rwxr-xr-x).

Create an Empty File (touch)

ansible all -m file -a "path=/tmp/demo.txt state=touch"

• state=touch: Updates timestamp if file exists, or creates an empty one if it doesn't.

Copy File to Remote Hosts

Uploads a file from your Controller to the Managed Nodes.

ansible all -m copy -a "src=./local_file.txt dest=/tmp/remote_file.txt"

• src: Path on the Controller (your machine).

• dest: Path on the Remote (managed node).

Fetch File From Remote Hosts

Downloads a file from Managed Nodes to your Controller (Backup).

ansible all -m fetch -a "src=/etc/hosts dest=./backups flat=yes"

• flat=yes: Saves the file directly in the destination folder without creating a directory tree for every host.

Change Permissions/ownership

ansible all -m file -a "path=/tmp/demo.txt owner=ec2-user group=ec2-user mode=0644" -b

• Why -b?: Changing ownership usually requires root if you don't own the file.

Delete a File or Directory

ansible all -m file -a "path=/tmp/file.txt state=absent"

• state=absent: Recursively deletes directories or unlinks files.

File Content Modification (lineinfile)

Append a Line

Adds a line to a file if it doesn't exist.

ansible all -m lineinfile -a "path=/etc/motd line='Welcome to the server!'" -b

Replace a Line (regex)

Search for a line and replace it (e.g., Disabling Root Login in SSH).

ansible all -m lineinfile -a "path=/etc/ssh/sshd_config regexp='^PermitRootLogin' line='PermitRootLogin no'" -b

• regexp: Regular expression to find the line.

• line: The text that should replace the found line.

User & Group Management

Create a Group

ansible all -m group -a "name=devops state=present" -b

Create a User

ansible all -m user -a "name=devops state=present" -b

Add User to a Group

Adds user devops to group wheel (sudoers) without removing them from other groups.

ansible all -m user -a "name=devops groups=wheel append=yes" -b

• append=yes: Very Important! If you forget this, the user will be removed from all other groups and only be in wheel.

Shell & Script Execution

Shell Module (complex Commands)

Use shell when you need pipes |, redirects >, or wildcards *.

ansible all -m shell -a "ls /var/log/*.log"

• Difference: The command module would fail here because it doesn't understand *.

Script Module (run Local Scripts Remotely)

Executes a script located on your Controller machine on the Remote nodes. It copies it automatically, runs it, and then deletes it.

1. Create the script locally (deploy.sh):

#!/bin/bash
sudo yum install -y httpd
sudo systemctl start httpd
sudo systemctl enable httpd

2. Run it via Ansible:

ansible all -m script -a "./deploy.sh"