How to get the installed yum packages with Ansible?

I am trying to get all the installed yum package on an RHEL machine. I can easily get it through using shell commands which is not idempotent and would like to use the yum command instead.

Shell command works fine:

- name: yum list packages
  shell: yum list installed > build_server_info.config

But when I try to use the yum command it just executes but do not give any results:

- name: yum_command 
  action: yum list=${pkg} list=available

I can easily get it through using shell commands which is not idempotent

You can't really talk about idempotence, when you are querying the current state of a machine.

"Idempontent" means that the task will ensure the machine is in the desired state no matter how many times you run a certain task.

When you query current state, you don't describe the desired state. No matter what you do, what method you use, the term "idempotent" is just not applicable.

Regarding your example, which does not give you results - you have repeated twice the same argument list and the task should fail (it doesn't, which looks like an Ansible quirk).

To get a list of installed packages, you should use:

- name: yum_command 
  yum:
    list=installed
  register: yum_packages

- debug:
    var: yum_packages

It saves a list of dictionaries describing each package to a variable yum_packages.

You can then use a JSON Query Filter to get a single package (tar):

- debug: var=item
  with_items: "{{yum_packages|json_query(jsonquery)}}"
  vars:
    jsonquery: "results[?name=='tar']"

to get a result like this:

"item": {
    "arch": "x86_64",
    "epoch": "2",
    "name": "tar",
    "nevra": "2:tar-1.26-31.el7.x86_64",
    "release": "31.el7",
    "repo": "installed",
    "version": "1.26",
    "yumstate": "installed"
}

Or only its version:

- debug: var=item
  with_items: "{{yum_packages|json_query(jsonquery)}}"
  vars:
    jsonquery: "results[?name=='tar'].version"

"item": "1.26"

Since Ansible 2.5, you can also use the package_facts module: it will gather the list of installed packages as Ansible facts.

Example from the docs:

- name: get the rpm package facts
  package_facts:
    manager: rpm

- name: show them
  debug: var=ansible_facts.packages

Well, the official Ansible documentation for the yum module describes list as:

"Various (non-idempotent) commands for usage with /usr/bin/ansible and not playbooks."

so you're going to be out of luck with finding an idempotent list invocation.

If you just want to suppress the changed output, set the changed_when parameter to False.

(Also, having the duplicate list parameter is suspicious.)

来源：https://stackoverflow.com/questions/41551620/how-to-get-the-installed-yum-packages-with-ansible

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ansible

ansible-playbook

idempotent