nixos-generate-config - Man Page

nixos-generate-config [--force] [--root root] [--dir dir]

This command writes two NixOS configuration modules:

/etc/nixos/hardware-configuration​.nix

This module sets NixOS configuration options based on your current hardware configuration​. In particular, it sets the fileSystem option to reflect all currently mounted file systems, the swapDevices option to reflect active swap devices, and the boot​.initrd​.* options to ensure that the initial ramdisk contains any kernel modules necessary for mounting the root file system​.

If this file already exists, it is overwritten​. Thus, you should not modify it manually​. Rather, you should include it from your /etc/nixos/configuration​.nix, and re-run nixos-generate-config to update it whenever your hardware configuration changes​.

/etc/nixos/configuration​.nix

This is the main NixOS system configuration module​. If it already exists, it’s left unchanged​. Otherwise, nixos-generate-config will write a template for you to customise​.

This command accepts the following options:

--root

If this option is given, treat the directory root as the root of the file system​. This means that configuration files will be written to root/etc/nixos, and that any file systems outside of root are ignored for the purpose of generating the fileSystems option​.

--dir

If this option is given, write the configuration files to the directory dir instead of /etc/nixos​.

--force

Overwrite /etc/nixos/configuration​.nix if it already exists​.

--no-filesystems

Omit everything concerning file systems and swap devices from the hardware configuration​.

--show-hardware-config

Don't generate configuration​.nix or hardware-configuration​.nix and print the hardware configuration to stdout only​.

This command is typically used during NixOS installation to write initial configuration modules​. For example, if you created and mounted the target file systems on /mnt and /mnt/boot, you would run:

$ nixos-generate-config --root /mnt

The resulting file /mnt/etc/nixos/hardware-configuration​.nix might look like this:

# Do not modify this file!  It was generated by ‘nixos-generate-config’
# and may be overwritten by future invocations​.  Please make changes
# to /etc/nixos/configuration​.nix instead​.
{ config, pkgs, ​.​.​. }:

{
  imports =
    [ <nixos/modules/installer/scan/not-detected​.nix>
    ];

  boot​.initrd​.availableKernelModules = [ "ehci_hcd" "ahci" ];
  boot​.kernelModules = [ "kvm-intel" ];
  boot​.extraModulePackages = [ ];

  fileSystems​."/" =
    { device = "/dev/disk/by-label/nixos";
      fsType = "ext3";
      options = [ "rw" "data=ordered" "relatime" ];
    };

  fileSystems​."/boot" =
    { device = "/dev/sda1";
      fsType = "ext3";
      options = [ "rw" "errors=continue" "user_xattr" "acl" "barrier=1" "data=writeback" "relatime" ];
    };

  swapDevices =
    [ { device = "/dev/sda2"; }
    ];

  nix​.maxJobs = 8;
}

It will also create a basic /mnt/etc/nixos/configuration​.nix, which you should edit to customise the logical configuration of your system​. This file includes the result of the hardware scan as follows:

  imports = [ ​./hardware-configuration​.nix ];

After installation, if your hardware configuration changes, you can run:

$ nixos-generate-config

to update /etc/nixos/hardware-configuration​.nix​. Your /etc/nixos/configuration​.nix will not be overwritten​.

Eelco Dolstra

Copyright © 2007-2020 Eelco Dolstra