Ansible OEL 8 DevOps · OEL 8 · Beginner

Ansible — Ad-hoc Commands

One-shot Ansible commands for everyday ops — checking uptime, restarting services, pushing files, running quick SQL — without writing a playbook. The 12 modules you'll reach for 80% of the time.

Anatomy of an Ad-hoc Command

Every ad-hoc command has the same shape:

BASH — ad-hoc command shape

ansible <host-pattern> -m <module-name> -a "<module-args>" [options]
#         └─────┬─────┘  └────┬─────┘  └────────┬────────┘
#               │              │                 │
#               │              │                 └─ key=value pairs the module accepts
#               │              └─ which Ansible module to run
#               └─ which hosts from inventory (group, single host, all, or a pattern)

For example: ansible databases -m ansible.builtin.ping runs the ping module against every host in the databases group from your inventory.

The 12 Most-Useful Modules for Ad-hoc Use

Module	What it does	One-line example
`ping`	Verifies SSH + Python work	`-m ping`
`setup`	Dumps all gathered facts	`-m setup -a "filter=ansible_distribution*"`
`command`	Runs a binary (no shell)	`-m command -a "uptime"`
`shell`	Runs through /bin/sh (pipes, redirects)	`-m shell -a "ps -ef \| grep mysql"`
`copy`	Pushes a file from control node	`-m copy -a "src=/etc/motd dest=/etc/motd"`
`fetch`	Pulls a file from managed node	`-m fetch -a "src=/etc/hostname dest=./tmp"`
`file`	Sets file/dir permissions, ownership	`-m file -a "path=/var/log mode=0755"`
`service`	Start / stop / restart a service	`-m service -a "name=nginx state=restarted"`
`systemd`	Same but systemd-aware	`-m systemd -a "name=mysqld state=started enabled=true"`
`dnf`	Install / remove RPM packages	`-m dnf -a "name=htop state=present"`
`user`	Create / modify a Linux user	`-m user -a "name=appuser state=present"`
`uri`	HTTP request from the remote host	`-m uri -a "url=https://example.com"`

Real-World Recipes

BASH — ad-hoc recipes you'll use weekly

# 1. Are all my db hosts reachable?
ansible databases -m ping

# 2. What kernel is each host running?
ansible all -m shell -a "uname -r"

# 3. How much disk free on / for every host?
ansible all -m shell -a "df -h / | tail -1"

# 4. Restart MySQL on a single node
ansible db1.example.com -m systemd -a "name=mysqld state=restarted" --become

# 5. Push a new my.cnf to all MySQL primaries
ansible mysql_primary -m copy \
  -a "src=./files/my.cnf dest=/etc/my.cnf owner=root mode=0644 backup=yes" \
  --become

# 6. Install htop everywhere
ansible all -m dnf -a "name=htop state=present" --become

# 7. Create the deploy user on a fresh box
ansible newbox -m user \
  -a "name=deploy shell=/bin/bash groups=wheel append=true" \
  --become

# 8. Run a SQL one-liner on every primary
ansible mysql_primary -m community.mysql.mysql_query \
  -a "login_user=root login_password=secret query='SHOW MASTER STATUS'"

# 9. Tail the last 50 lines of a log
ansible web -m shell -a "tail -50 /var/log/nginx/error.log" --become

# 10. Reboot a host and wait for it to come back
ansible db2.example.com -m reboot --become

Quoting Rules — The Single Biggest Beginner Trap

Ansible's -a argument is parsed as a string of key=value pairs. If a value contains spaces, quote it. If it contains both spaces and quotes, escape the inner ones. Examples:

BASH — quoting

# Single key=value, no spaces — no quotes needed
ansible all -m ping

# Spaces in a value — wrap the whole thing in single quotes
ansible all -m shell -a 'echo Hello World'

# A nested quote — escape with backslash, or use single + double mix
ansible all -m shell -a 'mysql -e "SELECT VERSION()"'

# When using YAML-style args (clearer for complex calls):
ansible all -m copy -a "src=hello.txt dest=/tmp/hello.txt mode='0644'"

Limit Targets, Verbosity, and Dry-Run

Flag	What it does
`--limit pattern`	Restricts the run to a subset of the host pattern
`--check`	Dry-run — show what would change, without making changes (most modules support it)
`--diff`	Show the line-level diff for files / templates that would change
`-v` / `-vv` / `-vvv`	Increase verbosity (last one prints the SSH commands themselves)
`-K`	Prompt for the sudo password (useful when NOPASSWD is not configured)
`-u username`	Override the SSH connection user for this command

✅ Tip: Use --check --diff together as your default safety net. --check simulates without making changes; --diff shows you exactly what would change. If both come back clean, you can run for real.