How I use Ansible and anacron for automation

With anacron, I can drop scripts and Ansible playbooks into place for all manner of trivial tasks.
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WOCinTech Chat. Modified by CC BY-SA 4.0

Automation is the great IT and DevOps ideal, but in my experience, anything that's not immediately convenient may as well not exist at all. There have been many times when I've come up with a pretty good solution for some task, and I'll even script it, but I stop short of making it literally automated because the infrastructure for easy automation doesn't exist on the machine I'm working on.

My favorite easy automation tool used to be the cron system—old, reliable, user-facing, and (aside from a scheduling syntax I can never commit to memory) simple. However, the problem with cron is that it assumes a computer is on 24 hours a day, every day. After missing one too many scheduled backups, I discovered anacron, the cron system based on timestamps rather than scheduled times. If your computer is off when a job would typically have run, anacron ensures that it's run when the computer is back on. Creating a job is as easy as dropping a shell script into one of three directories: cron.daily, cron.weekly, or cron.monthly (you can define more if you want). With anacron, I find myself dropping scripts and Ansible playbooks into place for all manner of trivial tasks, including pop-up reminders of upcoming due dates or events.

It's a simple and obvious solution to a modern problem, but it does me no good if anacron isn't installed on the computer.

Software setup with Ansible

Any time I set up a new computer, whether it's a laptop, workstation, or server, I install anacron. That's easy, but an anacron install only provides the anacron command. It doesn't set up the anacron user environment. So I created an Ansible playbook to set up what the user needs to use anacron and install the anacron command.

First, the standard Ansible boilerplate:

- hosts: localhost

Creating directories with Ansible

Next, I create the directory tree I use for anacron. You can think of this as a sort of transparent crontab.

    - name: create directory tree
        path: "{{ item }}"
        state: directory
        - '~/.local/etc/cron.daily'
        - '~/.local/etc/cron.weekly'
        - '~/.local/etc/cron.monthly'
        - '~/.var/spool/anacron'

The syntax of this might seem a little strange, but it's actually a loop. The with_items: directive defines four directories to create, and Ansible iterates over the ansible.builtin.file: directive once for each directory (the directory name populates the {{ item }} variable). As with everything in Ansible, there's no error or conflict if the directory already exists.

Copying files with Ansible

The ansible.builtin.copy module copies files from one location to another. For this to work, I needed to create a file called anacrontab. It's not an Ansible playbook, so I keep it in my ~/Ansible/data directory, where I keep support files for my playbooks.

    - name: copy anacrontab into place
        src: ~/Ansible/data/anacrontab
        dest: ~/.local/etc/anacrontab
        mode: '0755'

My anacrontab file is simple and mimics the one some distributions install by default into /etc/anacron:

1  0    run-parts $HOME/.local/etc/cron.daily/
7  0  cron.wek    run-parts $HOME/.local/etc/cron.weekly/
30 0  cron.mon    run-parts $HOME/.local/etc/cron.monthly/

Running anacron on login

Most Linux distributions configure anacron to read jobs from /etc/anacron. I mostly use anacron as a regular user, so I launch anacron from my login ~/.profile. I don't want to have to remember to configure that myself, so I have Ansible do it. I use the ansible.builtin.lineinfile module, which creates ~/.profile if it doesn't already exist and inserts the anacron launch line.

    - name: add local anacrontab to .profile
        path: ~/.profile
        regexp: '^/usr/sbin/anacron'
        line: '/usr/sbin/anacron -t ~/.local/etc/anacrontab'
        create: true

Installing anacron with Ansible

For most of my systems, the dnf module would work for package installation, but my workstation runs Slackware (which uses slackpkg), and sometimes a different Linux distro makes its way into my collection. The ansible.builtin.package module provides a generic interface to package installation, so I use it for this playbook. Luckily, I haven't come across a repo that names anacron anything but anacron, so for now, I don't have to account for potential differences in package names.

This is actually a separate play because package installation requires privilege escalation, provided by the becomes: true directive.

- hosts: localhost
  become: true
    - name: install anacron
        name: anacron
        state: present

Using anacron and Ansible for easy automation

To install anacron with Ansible, I run the playbook:

$ ansible-playbook ~/Ansible/setup-anacron.yaml

From then on, I can write shell scripts to perform some trivial but repetitive task and copy it into ~/.local/etc/cron.daily to have it automatically run once a day (or thereabouts). I also write Ansible playbooks for tasks such as cleaning out my downloads folder. I place my playbooks in ~/Ansible, which is where I keep my Ansible plays, and then create a shell script in ~/.local/etc/cron.daily to execute the play. It's easy, painless, and quickly becomes second nature.

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Seth Kenlon
Seth Kenlon is a UNIX geek, free culture advocate, independent multimedia artist, and D&D nerd. He has worked in the film and computing industry, often at the same time.

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