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this post was submitted on 14 Feb 2024
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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
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Another aspect I like about Nix compared to what I understand from Ansible (which I used a bit but not much) is that your configuration describes your system without any hidden state. Yes, you only get your dependencies through full evaluation, but what I mean is this: Let's say you install something on a system, i.e. you add it to your list of packages, which you later remove. To my knowledge, Ansible won't remove the package if not explicitly asked. However, if you explicitly tell Ansible to not have it installed, what happens if that package is later introduced as a dependency?
Ansible will always operate on a stateful system, which is kind of the combination of what others have already mentioned – it's (EDIT: it being Nix) idempotent and there's no hidden state that will break something down the way.
Ansible works on tasks, and to your hypothetical there, if you have a task that calls the package manager to put a package in the state 'absent', but it is another package's dependency, it will have little to do with ansible, and just follow the package manager's behaviour. (Up to some details. Like for 'apt', ansible runs the command with '-y', which has a little different behaviour than just removing the interaction part and assuming yes). If the package manager removes the depending package, and your playbook has first a task that installs it, then a taks that removes the dependency, you will always get 'changed' on both tasks everytime you run the playbook, even if your playbook puts the machine in the same state as before.