As I mentioned earlier, NixOS can only manage system-level configuration. To manage user-level configuration in the Home directory, we need to install Home Manager.
According to the official [Home Manager Manual](https://nix-community.github.io/home-manager/index.xhtml), to install Home Manager as a module of NixOS, we first need to create `/etc/nixos/home.nix`. Here's an example of its contents:
After adding `/etc/nixos/home.nix`, you need to import this new configuration file in `/etc/nixos/flake.nix` to make use of it, use the following command to generate an example in the current folder for reference:
```shell
nix flake new example -t github:nix-community/home-manager#nixos
```
After adjusting the parameters, the content of `/etc/nixos/flake.nix` is as follows:
> If your system's hostname is not `my-nixos`, you need to modify the name of `nixosConfigurations` in `flake.nix`, or use `--flake /etc/nixos#my-nixos` to specify the configuration name.
After the installation, all user-level packages and configuration can be managed through `/etc/nixos/home.nix`. When running `sudo nixos-rebuild switch`, the configuration of home-manager will be applied automatically. (**It's not necessary to run `home-manager switch` manually**!)
To find the options we can use in `home.nix`, referring to the following documents:
- [Home Manager - Appendix A. Configuration Options](https://nix-community.github.io/home-manager/options.xhtml): A list of all options, it is recommended to search for keywords in it.
- [home-manager](https://github.com/nix-community/home-manager): Some options are not listed in the official documentation, or the documentation is not clear enough, you can directly search and read the corresponding source code in this home-manager repo.
There are many software packages or configurations that can be set up using either NixOS Modules (`configuration.nix`) or Home Manager (`home.nix`), which brings about a choice dilemma: **What is the difference between placing software packages or configuration files in NixOS Modules versus Home Manager, and how should one make a decision?**
First, let's look at the differences: Software packages and configuration files installed via NixOS Modules are global to the entire system. Global configurations are usually stored in `/etc`, and system-wide installed software is accessible in any user environment.
On the other hand, configurations and software installed via Home Manager will be linked to the respective user's Home directory. The software installed is only available in the corresponding user environment, and it becomes unusable when switched to another user.
Based on these characteristics, the general recommended usage is:
- NixOS Modules: Install system core components and other software packages or configurations needed by all users.
- For instance, if you want a software package to continue working when you switch to the root user, or if you want a configuration to apply system-wide, you should install it using NixOS Modules.
- Home Manager: Use Home Manager for all other configurations and software.
The benefits of this approach are:
1. Software and background services installed at the system level often run with root privileges. Avoiding unnecessary software installations at the system level can reduce the security risks of the system.
1. Many configurations in Home Manager are universal for NixOS, macOS, and other Linux distributions. Choosing Home Manager to install software and configure systems can improve the portability of configurations.
1. If you need multi-user support, software and configurations installed via Home Manager can better isolate different user environments, preventing configuration and software version conflicts between users.
## How to use packages installed by Home Manager with privileged access?
The first thing that comes to mind is to switch to `root`, but then any packages installed by the current user through `home.nix` will be unavailable.
let's take `kubectl` as an example(it's pre-installed via `home.nix`):
```sh
# 1. kubectl is available
› kubectl | head
kubectl controls the Kubernetes cluster manager.
Find more information at: https://kubernetes.io/docs/reference/kubectl/
......
# 2. switch user to `root`
› sudo su
# 3. kubectl is no longer available
> kubectl
Error: nu::shell::external_command
× External command failed
╭─[entry #1:1:1]
1 │ kubectl
· ───┬───
· ╰── executable was not found
╰────
help: No such file or directory (os error 2)
/home/ryan/nix-config> exit
```
But it's possible to run those packages with privileged access without switching to `root`, by using `sudo`, we temporarily grant the current user privileged access to system resources:
