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139 lines
6.1 KiB
139 lines
6.1 KiB
<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>
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The best way to keep your NixOS installation up to date is to use one of the
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NixOS <emphasis>channels</emphasis>. A channel is a Nix mechanism for
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distributing Nix expressions and associated binaries. The NixOS channels are
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updated automatically from NixOS’s Git repository after certain tests have
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passed and all packages have been built. These channels are:
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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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<literal
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xlink:href="https://nixos.org/channels/nixos-21.05">nixos-21.05</literal>.
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These only get conservative bug fixes and package upgrades. For instance,
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a channel update may cause the Linux kernel on your system to be upgraded
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from 4.19.34 to 4.19.38 (a minor bug fix), but not from
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4.19.<replaceable>x</replaceable> to 4.20.<replaceable>x</replaceable> (a
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major change that has the potential to break things). Stable channels are
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generally maintained until the next stable branch is created.
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</para>
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<para></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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<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 see
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radical changes between channel updates. It’s not recommended for
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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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<literal
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xlink:href="https://nixos.org/channels/nixos-21.05-small">nixos-21.05-small</literal>
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or
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<literal
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xlink:href="https://nixos.org/channels/nixos-unstable-small">nixos-unstable-small</literal>.
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These are identical to the stable and unstable channels described above,
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except that they contain fewer binary packages. This means they get
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updated faster than the regular channels (for instance, when a critical
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security patch is committed to NixOS’s source tree), but may require
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more packages to be built from source than usual. They’re mostly
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intended for server 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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To see what channels are available, go to
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<link 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 latest
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version and includes ISO images and VirtualBox appliances.) Please note that
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during the release process, channels that are not yet released will be
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present here as well. See the Getting NixOS page
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<link xlink:href="https://nixos.org/nixos/download.html"/> to find the newest
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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 NixOS
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channel that corresponds to your installation source. For instance, if you
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installed from a 21.05 ISO, you will be subscribed to the
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<literal>nixos-21.05</literal> channel. To see which NixOS channel you’re
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subscribed to, run the following as root:
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<screen>
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<prompt># </prompt>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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<prompt># </prompt>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 end.) For
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instance, to use the NixOS 21.05 stable channel:
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<screen>
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<prompt># </prompt>nix-channel --add https://nixos.org/channels/nixos-21.05 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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<prompt># </prompt>nix-channel --add https://nixos.org/channels/nixos-21.05-small nixos
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</screen>
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And if you want to live on the bleeding edge:
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<screen>
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<prompt># </prompt>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>
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You can then upgrade NixOS to the latest version in your chosen channel by
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running
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<screen>
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<prompt># </prompt>nixos-rebuild switch --upgrade
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</screen>
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which is equivalent to the more verbose <literal>nix-channel --update nixos;
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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 <literal> nix-channel
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--add</literal> as a non root user (or without sudo) will not affect
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configuration in <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. The only
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exception is that a newer NixOS may also have a newer Nix version, which may
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involve an upgrade of Nix’s database schema. This cannot be undone easily,
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so in that case you will not be able 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 following
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to <filename>configuration.nix</filename>:
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<programlisting>
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<xref linkend="opt-system.autoUpgrade.enable"/> = true;
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<xref linkend="opt-system.autoUpgrade.allowReboot"/> = true;
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</programlisting>
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This enables a periodically executed systemd service named
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<literal>nixos-upgrade.service</literal>. If the <literal>allowReboot</literal>
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option is <literal>false</literal>, it runs <command>nixos-rebuild switch
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--upgrade</command> to upgrade NixOS to the latest version in the current
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channel. (To see when the service runs, see <command>systemctl list-timers</command>.)
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If <literal>allowReboot</literal> is <literal>true</literal>, then the
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system will automatically reboot if the new generation contains a different
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kernel, initrd or kernel modules.
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You can also specify a channel explicitly, e.g.
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<programlisting>
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<xref linkend="opt-system.autoUpgrade.channel"/> = https://nixos.org/channels/nixos-21.05;
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</programlisting>
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</para>
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</section>
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</chapter>
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