2014-08-24 19:18:18 +02:00
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<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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version="5.0"
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xml:id="sec-upgrading">
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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 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 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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<itemizedlist>
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<listitem>
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<para><emphasis>Stable channels</emphasis>, such as <literal
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xlink:href="https://nixos.org/channels/nixos-14.12">nixos-14.12</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). Stable channels are generally
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maintained until the next stable branch is created.</para>
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<para></para>
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</listitem>
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<listitem>
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<para>The <emphasis>unstable channel</emphasis>, <literal
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xlink:href="https://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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<listitem>
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<para><emphasis>Small channels</emphasis>, such as <literal
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xlink:href="https://nixos.org/channels/nixos-14.12-small">nixos-14.12-small</literal>
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or <literal
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xlink:href="https://nixos.org/channels/nixos-unstable-small">nixos-unstable-small</literal>. These
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are identical to the stable and unstable channels described above,
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except that they contain fewer binary packages. This means they
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get updated faster than the regular channels (for instance, when a
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critical security patch is committed to NixOS’s source tree), but
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may require more packages to be built from source than
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usual. They’re mostly intended for server environments and as such
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contain few GUI applications.</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="https://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 14.12 ISO, you will be subscribed to
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the <literal>nixos-14.12</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 --list | grep nixos
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nixos https://nixos.org/channels/nixos-unstable
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</screen>
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To switch to a different NixOS channel, do
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<screen>
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$ nix-channel --add https://nixos.org/channels/<replaceable>channel-name</replaceable> nixos
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</screen>
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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 14.12 stable channel:
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<screen>
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$ nix-channel --add https://nixos.org/channels/nixos-14.12 nixos
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</screen>
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If you have a server, you may want to use the “small” channel instead:
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<screen>
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$ nix-channel --add https://nixos.org/channels/nixos-14.12-small nixos
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</screen>
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2014-12-30 22:31:01 +01:00
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And if you want to live on the bleeding edge:
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<screen>
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$ nix-channel --add https://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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</chapter>
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