Manual: Document how to use NixOS channels
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Eelco Dolstra
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@ -89,9 +89,14 @@ running NixOS system through several other means:
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<listitem><para>For initialising Ext4 partitions:
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<command>mkfs.ext4</command>. It is recommended that you assign a
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unique symbolic label to the file system using the option
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<option>-L <replaceable>label</replaceable></option>. This will
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make the file system configuration independent from device
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changes.</para></listitem>
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<option>-L <replaceable>label</replaceable></option>, since this
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makes the file system configuration independent from device
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changes. For example:
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<screen>
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$ mkfs.ext4 -L nixos /dev/sda1</screen>
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</para></listitem>
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<listitem><para>For creating swap partitions:
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<command>mkswap</command>. Again it’s recommended to assign a
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@ -124,6 +129,12 @@ $ mount /dev/disk/by-label/nixos /mnt
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</para></listitem>
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<listitem><para>If your machine has a limited amount of memory, you
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may want to activate swap devices now (<command>swapon
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<replaceable>device</replaceable></command>). The installer (or
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rather, the build actions that it may spawn) may need quite a bit of
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RAM, depending on your configuration.</para></listitem>
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<listitem>
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<para>You now need to create a file
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@ -188,28 +199,16 @@ $ nano /mnt/etc/nixos/configuration.nix
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</listitem>
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<listitem><para>If your machine has a limited amount of memory, you
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may want to activate swap devices now (<command>swapon
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<replaceable>device</replaceable></command>). The installer (or
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rather, the build actions that it may spawn) may need quite a bit of
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RAM, depending on your configuration.</para></listitem>
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<!--
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<listitem><para>Optionally, you can run
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<screen>
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$ nixos-checkout</screen>
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to make the installer use the latest NixOS/Nixpkgs sources from the
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Git repository, rather than the sources on CD.</para></listitem>
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-->
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<listitem><para>Do the installation:
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<screen>
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$ nixos-install</screen>
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Cross fingers.</para></listitem>
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Cross fingers. If this fails due to a temporary problem (such as
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a network issue while downloading binaries from the NixOS binary
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cache), you can just re-run <command>nixos-install</command>.
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Otherwise, fix your <filename>configuration.nix</filename> and
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then re-run <command>nixos-install</command>.</para></listitem>
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<listitem><para>If everything went well:
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@ -221,7 +220,7 @@ $ reboot</screen>
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<listitem>
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<para>You should now be able to boot into the installed NixOS.
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The Grub boot menu shows a list of <emphasis>available
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The GRUB boot menu shows a list of <emphasis>available
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configurations</emphasis> (initially just one). Every time you
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change the NixOS configuration (see <xref
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linkend="sec-changing-config" />), a new item appears in the menu.
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@ -256,20 +255,20 @@ $ nix-env -i w3m</screen>
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</orderedlist>
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<para><xref linkend="ex-install-sequence" /> shows a typical sequence
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of commands for installing NixOS on an empty hard drive (here
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<filename>/dev/sda</filename>). <xref linkend="ex-config" /> shows a
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corresponding configuration Nix expression.</para>
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<para>To summarise, <xref linkend="ex-install-sequence" /> shows a
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typical sequence of commands for installing NixOS on an empty hard
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drive (here <filename>/dev/sda</filename>). <xref linkend="ex-config"
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/> shows a corresponding configuration Nix expression.</para>
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<example xml:id='ex-install-sequence'><title>Commands for installing NixOS on <filename>/dev/sda</filename></title>
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<screen>
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$ fdisk /dev/sda <lineannotation>(or whatever device you want to install on)</lineannotation>
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$ mkfs.ext4 -L nixos /dev/sda1 <lineannotation>(idem)</lineannotation>
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$ mkswap -L swap /dev/sda2 <lineannotation>(idem)</lineannotation>
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$ mount LABEL=nixos /mnt
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$ nixos-generate-config
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$ fdisk /dev/sda # <lineannotation>(or whatever device you want to install on)</lineannotation>
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$ mkfs.ext4 -L nixos /dev/sda1
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$ mkswap -L swap /dev/sda2
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$ swapon /dev/sda2
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$ mount /dev/disk/by-label/nixos /mnt
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$ nixos-generate-config --root /mnt
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$ nano /mnt/etc/nixos/configuration.nix
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<lineannotation>(in particular, set the fileSystems and swapDevices options)</lineannotation>
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$ nixos-install
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$ reboot</screen>
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</example>
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@ -284,14 +283,12 @@ $ reboot</screen>
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boot.loader.grub.device = "/dev/sda";
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# Note: setting fileSystems and swapDevices is generally not
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# necessary, since nixos-generate-config has set them automatically
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# in hardware-configuration.nix.
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fileSystems."/".device = "/dev/disk/by-label/nixos";
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swapDevices =
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[ { device = "/dev/disk/by-label/swap"; } ];
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# Note: setting fileSystems is generally not
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# necessary, since nixos-generate-config figures them out
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# automatically in hardware-configuration.nix.
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#fileSystems."/".device = "/dev/disk/by-label/nixos";
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# Enable the OpenSSH server.
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services.sshd.enable = true;
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}</screen>
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</example>
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@ -317,6 +314,10 @@ to build the new configuration, make it the default configuration for
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booting, and try to realise the configuration in the running system
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(e.g., by restarting system services).</para>
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<warning><para>These commands must be executed as root, so you should
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either run them from a root shell or by prefixing them with
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<literal>sudo -i</literal>.</para></warning>
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<para>You can also do
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<screen>
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@ -336,6 +337,18 @@ to build the configuration and make it the boot default, but not
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switch to it now (so it will only take effect after the next
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reboot).</para>
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<para>You can make your configuration show up in a different submenu
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of the GRUB 2 boot screen by giving it a different <emphasis>profile
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name</emphasis>, e.g.
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<screen>
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$ nixos-rebuild switch -p test </screen>
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which causes the new configuration (and previous ones created using
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<literal>-p test</literal>) to show up in the GRUB submenu “NixOS -
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Profile 'test'”. This can be useful to separate test configurations
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from “stable” configurations.</para>
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<para>Finally, you can do
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<screen>
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@ -346,7 +359,7 @@ whether everything compiles cleanly.</para>
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<para>If you have a machine that supports hardware virtualisation, you
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can also test the new configuration in a sandbox by building and
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running a <emphasis>virtual machine</emphasis> that contains the
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running a QEMU <emphasis>virtual machine</emphasis> that contains the
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desired configuration. Just do
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<screen>
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@ -361,7 +374,6 @@ available.</para>
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</section>
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<!--===============================================================-->
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<section xml:id="sec-upgrading">
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@ -369,28 +381,85 @@ available.</para>
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<title>Upgrading NixOS</title>
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<para>The best way to keep your NixOS installation up to date is to
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use the <literal>nixos-unstable</literal> channel. (A channel is a
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use one of the NixOS <emphasis>channels</emphasis>. A channel is a
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Nix mechanism for distributing Nix expressions and associated
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binaries.) The NixOS channel is updated automatically from NixOS’s
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Git repository after running certain tests and building most
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packages.</para>
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binaries. The NixOS channels are updated automatically from NixOS’s
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Git repository after certain tests have passed and all packages have
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been built. These channels are:
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<para>NixOS automatically subscribes you to the NixOS channel. If for
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some reason this is not the case, just do
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<itemizedlist>
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<listitem>
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<para>Stable channels, such as <literal
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xlink:href="http://nixos.org/channels/nixos-13.10">nixos-13.10</literal>.
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These only get conservative bug fixes and package upgrades. For
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instance, a channel update may cause the Linux kernel on your
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system to be upgraded from 3.4.66 to 3.4.67 (a minor bug fix), but
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not from 3.4.<replaceable>x</replaceable> to
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3.11.<replaceable>x</replaceable> (a major change that has the
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potential to break things).</para>
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</listitem>
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<listitem>
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<para>The unstable channel, <literal
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xlink:href="http://nixos.org/channels/nixos-unstable">nixos-unstable</literal>.
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This corresponds to NixOS’s main development branch, and may thus
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see radical changes between channel updates. It’s not recommended
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for production systems.</para>
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</listitem>
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</itemizedlist>
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To see what channels are available, go to <link
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xlink:href="http://nixos.org/channels"/>. (Note that the URIs of the
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various channels redirect to a directory that contains the channel’s
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latest version and includes ISO images and VirtualBox
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appliances.)</para>
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<para>When you first install NixOS, you’re automatically subscribed to
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the NixOS channel that corresponds to your installation source. For
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instance, if you installed from a 13.10 ISO, you will be subscribed to
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the <literal>nixos-13.10</literal> channel. To see which NixOS
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channel you’re subscribed to, run the following as root:
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<screen>
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$ nix-channel --add http://nixos.org/channels/nixos-unstable
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$ nix-channel --list | grep nixos
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nixos https://nixos.org/channels/nixos-unstable
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</screen>
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You can then upgrade NixOS to the latest version in the channel by
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running
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To switch to a different NixOS channel, do
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<screen>
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$ nix-channel --update nixos
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$ nix-channel --add http://nixos.org/channels/<replaceable>channel-name</replaceable> nixos
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</screen>
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and running the <command>nixos-rebuild</command> command as described
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in <xref linkend="sec-changing-config"/>.</para>
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(Be sure to include the <literal>nixos</literal> parameter at the
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end.) For instance, to use the NixOS 13.10 stable channel:
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<screen>
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$ nix-channel --add http://nixos.org/channels/nixos-13.10 nixos
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</screen>
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But it you want to live on the bleeding edge:
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<screen>
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$ nix-channel --add http://nixos.org/channels/nixos-unstable nixos
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</screen>
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</para>
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<para>You can then upgrade NixOS to the latest version in your chosen
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channel by running
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<screen>
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$ nixos-rebuild switch --upgrade
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</screen>
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which is equivalent to the more verbose <literal>nix-channel --update
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nixos; nixos-rebuild switch</literal>.</para>
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<warning><para>It is generally safe to switch back and forth between
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channels. The only exception is that a newer NixOS may also have a
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newer Nix version, which may involve an upgrade of Nix’s database
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schema. This cannot be undone easily, so in that case you will not be
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able to go back to your original channel.</para></warning>
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</section>
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