This chapter describes how to configure various aspects of a NixOS machine through the configuration file /etc/nixos/configuration.nix. As described in , changes to that file only take effect after you run nixos-rebuild.

Secure shell (SSH) access to your machine can be enabled by setting: services.openssh.enable = true; By default, root logins using a password are disallowed. They can be disabled entirely by setting services.openssh.permitRootLogin to "no". You can declaratively specify authorised RSA/DSA public keys for a user as follows: users.extraUsers.alice.openssh.authorizedKeys.keys = [ "ssh-dss AAAAB3NzaC1kc3MAAACBAPIkGWVEt4..." ];

By default, NixOS uses DHCP (specifically, (dhcpcd)) to automatically configure network interfaces. However, you can configure an interface manually as follows: networking.interfaces.eth0 = { ipAddress = "192.168.1.2"; prefixLength = 24; }; (The network prefix can also be specified using the option subnetMask, e.g. "255.255.255.0", but this is deprecated.) Typically you’ll also want to set a default gateway and set of name servers: networking.defaultGateway = "192.168.1.1"; networking.nameservers = [ "8.8.8.8" ]; Statically configured interfaces are set up by the systemd service interface-name-cfg.service. The default gateway and name server configuration is performed by network-setup.service. The host name is set using networking.hostName: networking.hostName = "cartman"; The default host name is nixos. Set it to the empty string ("") to allow the DHCP server to provide the host name.

IPv6 is enabled by default. Stateless address autoconfiguration is used to automatically assign IPv6 addresses to all interfaces. You can disable IPv6 support globally by setting: networking.enableIPv6 = false;

NixOS has a simple stateful firewall that blocks incoming connections and other unexpected packets. The firewall applies to both IPv4 and IPv6 traffic. It can be enabled as follows: networking.firewall.enable = true; You can open specific TCP ports to the outside world: networking.firewall.allowedTCPPorts = [ 80 443 ]; Note that TCP port 22 (ssh) is opened automatically if the SSH daemon is enabled (services.openssh.enable = true). UDP ports can be opened through networking.firewall.allowedUDPPorts. Also of interest is networking.firewall.allowPing = true; to allow the machine to respond to ping requests. (ICMPv6 pings are always allowed.)

NixOS will start wpa_supplicant for you if you enable this setting: networking.wireless.enable = true; NixOS currently does not generate wpa_supplicant's configuration file, /etc/wpa_supplicant.conf. You should edit this file yourself to define wireless networks, WPA keys and so on (see wpa_supplicant.conf(5)). If you are using WPA2 the wpa_passphrase tool might be useful to generate the wpa_supplicant.conf. $ wpa_passphrase ESSID PSK > /etc/wpa_supplicant.conf After you have edited the wpa_supplicant.conf, you need to restart the wpa_supplicant service. $ systemctl restart wpa_supplicant.service

You can use networking.localCommands to specify shell commands to be run at the end of network-setup.service. This is useful for doing network configuration not covered by the existing NixOS modules. For instance, to statically configure an IPv6 address: networking.localCommands = '' ip -6 addr add 2001:610:685:1::1/64 dev eth0 '';