# When to use \`nix-env\` over configuration.nix (new to NixOS)
**URL:** https://discourse.nixos.org/t/when-to-use-nix-env-over-configuration-nix-new-to-nixos/33921
**Category:** Uncategorized
**Created:** [October 6, 2023, 10:12pm UTC](https://discourse.nixos.org/t/when-to-use-nix-env-over-configuration-nix-new-to-nixos/33921 "2023-10-06T22:12:38Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@heartbeast42](https://discourse.nixos.org/u/heartbeast42)
#### Post date: [October 6, 2023, 10:12pm UTC](https://discourse.nixos.org/t/when-to-use-nix-env-over-configuration-nix-new-to-nixos/33921/1 "2023-10-06T22:12:38Z")
I’m a longtime Linux user, (mostly Debian & Debian downstream distros), getting used to NixOS.
I’m trying to understand:
- Under what circumstances should I use `nix-env` to install packages over specifying packages in `/etc/nixos/configuration.nix file`? I see `nix-env` mentioned but also it’s recommended that it not be used. Why does it exist then? Is it just for users without root or admin privileges to be able to install software?
- I’ve heard people mention that using `nix-env` “doesn’t give you the benefits of nix”.
– I know that installing software with `nix-env` won’t effect the boot version options.
– I know that the generations are managed separately
– but what all exactly is meant by “the benefits of nix”? Is it just those or something more?
Further context, as I’m using my system and learning NixOs and installing software, the longer my builds take when I run `sudo nixos-rebuild switch`. I’m inclined to use `nix-env` to install further software that doesn’t need to necessarily be installed on the system level to cut down on build times but I can’t help feeling like I’m doing something wrong, or is the recommended way of using NixOS truly to install everything possible through `configuration.nix` and make thy peace with longer and loooonger build times? If it is I can accept that, I just wanna make sure I’m using my system to it’s fullest.
Also apologies if the answer to this is obvious or front and center in the docs, I have it on my agenda to start working through the nix docs but I haven’t got around to it lately. Do feel free to include recommended reading in the docs or otherwise if you’re so inclined.
Thanks y’all!
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### Author:  [@uep](https://discourse.nixos.org/u/uep)
#### Post date: [October 6, 2023, 10:31pm UTC](https://discourse.nixos.org/t/when-to-use-nix-env-over-configuration-nix-new-to-nixos/33921/2 "2023-10-06T22:31:05Z")
It’s vastly over-simplifying things, but the basic reason there are both is that `nix-env -i` is for nix on other platforms, where you can’t manage the system more cohesively with `configuration.nix`. It’s an imperative “install thingX” method, equivalent to something like `brew install thingX` when nix is used as a third-party package manager.
As you go on, you’ll learn that the concept of “software being installed” at all is more nebulous, and there are many ways of managing what’s downloaded, what’s upgraded when, and what’s visible in the path in which context. Coming from other distributions, where everything is usually “installed” into the single global system, is something you will ‘unlearn’ to a degree.
Many of those other methods apply equally well on both NixOS and nix-on-other-platforms cases, and using those may also be preferable to `nix-env`, and so it will somewhat get left behind. Examples include:
- pulling something in to a project devshell, automatically with direnv, to get versioned and updated as part of a project rather than host schedule.
- managing your own applications via home-manager rather than via either system packages or `nix-env`
- using `nix-shell`, `nix shell`, `nix run`, etc for things you use infrequently, rather than “installing” them “in case”
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### Author:  [@sullyj3](https://discourse.nixos.org/u/sullyj3)
#### Post date: [October 6, 2023, 11:29pm UTC](https://discourse.nixos.org/t/when-to-use-nix-env-over-configuration-nix-new-to-nixos/33921/3 "2023-10-06T23:29:03Z")
> [@heartbeast42](#):
>
> but what all exactly is meant by “the benefits of nix”?
Mostly the ability to define your installed packages in a version controlled configuration file, that you can then use to reproduce your set of installed packages on another machine. If you install a bunch of stuff with `nix-env`, it’s not so easy to reproduce your setup.
In my opinion if you’re not concerned with this benefit and just want to use nix like an `apt` or `pacman` equivalent, using `nix-env` is a perfectly valid choice.
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### Author:  [@testplayername](https://discourse.nixos.org/u/testplayername)
#### Post date: [October 6, 2023, 11:57pm UTC](https://discourse.nixos.org/t/when-to-use-nix-env-over-configuration-nix-new-to-nixos/33921/4 "2023-10-06T23:57:20Z")
Check out [https://stop-using-nix-env.privatevoid.net/](https://stop-using-nix-env.privatevoid.net/) for some quick explanations on why `nix-env` should be avoided in (almost) all cases. Much more detailed discussion is in this [thread](https://discourse.nixos.org/t/depreciate-the-use-of-nix-env-to-install-packages/20139/34).
For your specific questions:
- On why `nix-env` exists in the first place:
It is useful as a “low-level” plumbing command for other tools (e.g. Home Manager). These tools (should) have a high-level API that retains one of Nix’s main features: being able to define your NixOS configuration (among other things) in configuration files, written in a declarative language.
- Benefits of Nix:
As stated in the first point, one of Nix’s primary strengths is its use of declarative configurations. In practice, for NixOS, this means (nearly) the entire operating system is defined in `/etc/nixos/configuration.nix` and whatever other files `configuration.nix` imports. This declarative approach has many benefits, which I assume you are already aware of since you’re already experimenting with NixOS. Using `nix-env` instead of modifying `/etc/nixos/configuration.nix` to permanently install things go completely against this idea. But see below for temporary installations…
- On long build times:
When you add new packages to `/etc/nixos/configuration.nix` there is not much you can do to reduce the potentially long processing time. Subsequent `nixos-rebuild switch` commands that you run just to update already-installed packages should complete fairly quickly. If you want to install something temporarily, use [ephemeral shells](https://nix.dev/tutorials/first-steps/ad-hoc-shell-environments#ad-hoc-envs).
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### Author:  [@TLATER](https://discourse.nixos.org/u/TLATER)
#### Post date: [October 7, 2023, 6:42am UTC](https://discourse.nixos.org/t/when-to-use-nix-env-over-configuration-nix-new-to-nixos/33921/5 "2023-10-07T06:42:51Z")
> [@sullyj3](#):
>
> using `nix-env` is a perfectly valid choice.
It still has _very_ severe flaws even as an `apt` replacement, sadly, most of which _all_ users probably fall prey to unwittingly. Give the site linked by @testplayername a read, I think it can genuinely be called broken.
`nix-env` is still worth understanding to know how nix things work under the hood and to write tooling with yourself, without targeting experimental features. Avoid it otherwise.
If you _really_ need it, at least be very aware of its issues. It’s probably still an ok tool to learn with when you’re starting out if you’ve been warned about the problems.
I hope `nix profile` is stabilized soonish so we actually have a viable replacement for it, but that’s likely still a few years away.