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The nixos-enter program is part of NixOS. Before it runs provides a shell, the script mounts api filesystems like /proc and setups the profile and /etc of the target system. To use it, setup <code>/mnt</code> as described in the [https://nixos.org/nixos/manual/#sec-installation installation manual].

At the time of writting, the following <code>mount</code> commands should suffice:

$ mount -o bind /dev/disk/by-label/<ROOT_LABEL> /mnt/

$ # mount any partitions you might have; here we assume only home and nix exist

$ mkdir -p /mnt/{home,nix}

$ mount -o bind /dev/disk/by-label/<HOME_LABEL> /mnt/home

$ mount -o bind /dev/disk/by-label/<NIX_LABEL> /mnt/nix

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Then run <code>nixos-enter</code>:

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You should now be in your NixOS system, and should be able to adjust it by e.g. editing <code>/etc/nixos/configuration.nix</code> and running <code>nixos-rebuild switch</code> as usual. Remember that you may have to establish Internet access within the chroot for some commands.

= Troubleshooting =

== 1. nixos-rebuild fails with "System has not been booted with <program> as init system." ==

In some cases, such as when using [[Systemd-networkd|systemd-networkd]] as the [[Bootloader|bootloader]], [[Nixos-rebuild|nixos-rebuild]] commands might fail with a message similar to

error: System has not been booted with systemd as init system (PID 1). Can't operate.

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If you have tried to use <code>nixos-rebuild switch</code>, you can try <code>nixos-rebuild boot</code> instead. Should that also fail, you can append <code>NIXOS_SWITCH_USE_DIRTY_ENV=1</code> to the commands, which should bypass the error while also setting the proper boot entries, if the [[Bootloader|bootloader]] is detected.

Finally, should all else fail, <code>nixos-install</code> should work as a replacement changing the root.