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152 lines
6.4 KiB
152 lines
6.4 KiB
<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-upgrading">
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<title>Upgrading NixOS</title>
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<para>
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The best way to keep your NixOS installation up to date is to use
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one of the NixOS <emphasis>channels</emphasis>. A channel is a Nix
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mechanism for distributing Nix expressions and associated binaries.
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The NixOS channels are updated automatically from NixOS’s Git
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repository after certain tests have passed and all packages have
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been built. These channels are:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<emphasis>Stable channels</emphasis>, such as
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<link xlink:href="https://nixos.org/channels/nixos-21.11"><literal>nixos-21.11</literal></link>.
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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 4.19.34 to 4.19.38 (a minor bug fix),
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but not from 4.19.x to 4.20.x (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.
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</para>
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</listitem>
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<listitem>
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<para>
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The <emphasis>unstable channel</emphasis>,
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<link xlink:href="https://nixos.org/channels/nixos-unstable"><literal>nixos-unstable</literal></link>.
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This corresponds to NixOS’s main development branch, and may
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thus see radical changes between channel updates. It’s not
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recommended for production systems.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>Small channels</emphasis>, such as
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<link xlink:href="https://nixos.org/channels/nixos-21.11-small"><literal>nixos-21.11-small</literal></link>
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or
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<link xlink:href="https://nixos.org/channels/nixos-unstable-small"><literal>nixos-unstable-small</literal></link>.
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These are identical to the stable and unstable channels
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described above, except that they contain fewer binary packages.
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This means they get updated faster than the regular channels
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(for instance, when a critical security patch is committed to
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NixOS’s source tree), but may require more packages to be built
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from source than usual. They’re mostly intended for server
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environments and as such contain few GUI applications.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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To see what channels are available, go to
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<link xlink:href="https://nixos.org/channels">https://nixos.org/channels</link>.
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(Note that the URIs of the various channels redirect to a directory
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that contains the channel’s latest version and includes ISO images
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and VirtualBox appliances.) Please note that during the release
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process, channels that are not yet released will be present here as
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well. See the Getting NixOS page
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<link xlink:href="https://nixos.org/nixos/download.html">https://nixos.org/nixos/download.html</link>
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to find the newest supported stable release.
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</para>
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<para>
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When you first install NixOS, you’re automatically subscribed to the
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NixOS channel that corresponds to your installation source. For
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instance, if you installed from a 21.11 ISO, you will be subscribed
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to the <literal>nixos-21.11</literal> channel. To see which NixOS
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channel you’re subscribed to, run the following as root:
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</para>
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<programlisting>
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# nix-channel --list | grep nixos
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nixos https://nixos.org/channels/nixos-unstable
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</programlisting>
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<para>
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To switch to a different NixOS channel, do
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</para>
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<programlisting>
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# nix-channel --add https://nixos.org/channels/channel-name nixos
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</programlisting>
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<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 21.11 stable channel:
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</para>
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<programlisting>
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# nix-channel --add https://nixos.org/channels/nixos-21.11 nixos
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</programlisting>
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<para>
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If you have a server, you may want to use the <quote>small</quote>
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channel instead:
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</para>
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<programlisting>
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# nix-channel --add https://nixos.org/channels/nixos-21.11-small nixos
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</programlisting>
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<para>
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And if you want to live on the bleeding edge:
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</para>
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<programlisting>
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# nix-channel --add https://nixos.org/channels/nixos-unstable nixos
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</programlisting>
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<para>
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You can then upgrade NixOS to the latest version in your chosen
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channel by running
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</para>
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<programlisting>
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# nixos-rebuild switch --upgrade
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</programlisting>
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<para>
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which is equivalent to the more verbose
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<literal>nix-channel --update nixos; nixos-rebuild switch</literal>.
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</para>
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<note>
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<para>
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Channels are set per user. This means that running
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<literal>nix-channel --add</literal> as a non root user (or
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without sudo) will not affect configuration in
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<literal>/etc/nixos/configuration.nix</literal>
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</para>
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</note>
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<warning>
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<para>
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It is generally safe to switch back and forth between channels.
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The only exception is that a newer NixOS may also have a newer Nix
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version, which may involve an upgrade of Nix’s database schema.
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This cannot be undone easily, so in that case you will not be able
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to go back to your original channel.
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</para>
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</warning>
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<section xml:id="sec-upgrading-automatic">
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<title>Automatic Upgrades</title>
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<para>
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You can keep a NixOS system up-to-date automatically by adding the
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following to <literal>configuration.nix</literal>:
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</para>
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<programlisting language="bash">
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system.autoUpgrade.enable = true;
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system.autoUpgrade.allowReboot = true;
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</programlisting>
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<para>
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This enables a periodically executed systemd service named
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<literal>nixos-upgrade.service</literal>. If the
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<literal>allowReboot</literal> option is <literal>false</literal>,
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it runs <literal>nixos-rebuild switch --upgrade</literal> to
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upgrade NixOS to the latest version in the current channel. (To
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see when the service runs, see
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<literal>systemctl list-timers</literal>.) If
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<literal>allowReboot</literal> is <literal>true</literal>, then
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the system will automatically reboot if the new generation
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contains a different kernel, initrd or kernel modules. You can
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also specify a channel explicitly, e.g.
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</para>
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<programlisting language="bash">
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system.autoUpgrade.channel = https://nixos.org/channels/nixos-21.11;
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</programlisting>
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</section>
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</chapter>
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