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System Manager vs NixOS

This page explains the relationship between System Manager and NixOS, and when to use each.

What is NixOS?

NixOS is a complete Linux distribution built on Nix. The entire system - kernel, bootloader, packages, services, users - is configured declaratively and built atomically.

What is System Manager?

System Manager brings NixOS-style declarative configuration to other Linux distributions. It manages packages, services, and /etc files, but leaves the base system (kernel, bootloader, init) to your distribution.

If you're already running NixOS, you don't need System Manager - NixOS provides these capabilities natively.

Key Differences

Aspect NixOS System Manager
Base system Nix all the way down Your distro (Ubuntu, Debian, etc.)
Kernel Managed by Nix Managed by distro
Bootloader Managed by Nix Managed by distro
Users/Groups Managed declaratively Managed by distro
Package manager Only Nix Nix + distro's (apt, dnf, etc.)
Init system systemd (required) systemd (required)
Rollback Full system rollback Service/package rollback

When to Use NixOS

Choose NixOS when:

  • You want complete declarative control over everything
  • You're setting up new machines from scratch
  • You want atomic system upgrades with full rollback
  • You're comfortable with a less traditional Linux experience

When to Use System Manager

Choose System Manager when:

  • You can't or won't reinstall the OS
  • You need to configure existing non-NixOS machines
  • Your organization requires specific distributions (Ubuntu, RHEL, etc.)
  • You want gradual adoption of declarative configuration
  • You're managing cloud instances with vendor-supplied images

Module Compatibility

System Manager uses a subset of NixOS modules. Many modules work directly:

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# This works in both NixOS and System Manager
{
  environment.systemPackages = [ pkgs.htop ];

  systemd.services.myapp = {
    description = "My Application";
    wantedBy = [ "system-manager.target" ]; # NixOS uses different target
    serviceConfig.ExecStart = "${pkgs.myapp}/bin/myapp";
  };
}

Some NixOS modules don't apply to System Manager:

  • boot.* - Bootloader configuration
  • fileSystems.* - Filesystem mounts
  • users.users.* - User management (though this may change)
  • Hardware-specific modules

Migration Path

From Traditional Linux to System Manager

  1. Install Nix on your existing system
  2. Start managing services with System Manager
  3. Gradually move more configuration to Nix
  4. Keep using apt/dnf for things System Manager doesn't manage

From System Manager to NixOS

If you later decide to switch to NixOS:

  1. Your .nix configuration largely transfers over
  2. Add NixOS-specific modules (boot, filesystems, users)
  3. Install NixOS with your existing configuration as a base

From NixOS to System Manager

If you need to configure non-NixOS machines:

  1. Extract the service/package parts of your NixOS config
  2. Replace NixOS-specific targets with system-manager.target
  3. Use System Manager on your non-NixOS machines

Using Both Together

You can use NixOS and System Manager in the same infrastructure:

  • NixOS for servers you control completely
  • System Manager for servers with OS requirements
  • Same configuration patterns and skills for both

See Also