nixos docs: format =)

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Graham Christensen
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xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="sec-upgrading">
<title>Upgrading NixOS</title>
<para>The best way to keep your NixOS installation up to date is to
use one of the NixOS <emphasis>channels</emphasis>. A channel is a
Nix mechanism for distributing Nix expressions and associated
binaries. The NixOS channels are updated automatically from NixOSs
Git repository after certain tests have passed and all packages have
been built. These channels are:
<itemizedlist>
<listitem>
<para><emphasis>Stable channels</emphasis>, such as <literal
<title>Upgrading NixOS</title>
<para>
The best way to keep your NixOS installation up to date is to use one of the
NixOS <emphasis>channels</emphasis>. A channel is a Nix mechanism for
distributing Nix expressions and associated binaries. The NixOS channels are
updated automatically from NixOSs Git repository after certain tests have
passed and all packages have been built. These channels are:
<itemizedlist>
<listitem>
<para>
<emphasis>Stable channels</emphasis>, such as
<literal
xlink:href="https://nixos.org/channels/nixos-17.03">nixos-17.03</literal>.
These only get conservative bug fixes and package upgrades. For
instance, a channel update may cause the Linux kernel on your
system to be upgraded from 4.9.16 to 4.9.17 (a minor bug fix), but
not from 4.9.<replaceable>x</replaceable> to
4.11.<replaceable>x</replaceable> (a major change that has the
potential to break things). Stable channels are generally
maintained until the next stable branch is created.</para>
These only get conservative bug fixes and package upgrades. For instance,
a channel update may cause the Linux kernel on your system to be upgraded
from 4.9.16 to 4.9.17 (a minor bug fix), but not from
4.9.<replaceable>x</replaceable> to 4.11.<replaceable>x</replaceable> (a
major change that has the potential to break things). Stable channels are
generally maintained until the next stable branch is created.
</para>
<para></para>
</listitem>
<listitem>
<para>The <emphasis>unstable channel</emphasis>, <literal
</listitem>
<listitem>
<para>
The <emphasis>unstable channel</emphasis>,
<literal
xlink:href="https://nixos.org/channels/nixos-unstable">nixos-unstable</literal>.
This corresponds to NixOSs main development branch, and may thus
see radical changes between channel updates. Its not recommended
for production systems.</para>
</listitem>
<listitem>
<para><emphasis>Small channels</emphasis>, such as <literal
This corresponds to NixOSs main development branch, and may thus see
radical changes between channel updates. Its not recommended for
production systems.
</para>
</listitem>
<listitem>
<para>
<emphasis>Small channels</emphasis>, such as
<literal
xlink:href="https://nixos.org/channels/nixos-17.03-small">nixos-17.03-small</literal>
or <literal
xlink:href="https://nixos.org/channels/nixos-unstable-small">nixos-unstable-small</literal>. These
are identical to the stable and unstable channels described above,
except that they contain fewer binary packages. This means they
get updated faster than the regular channels (for instance, when a
critical security patch is committed to NixOSs source tree), but
may require more packages to be built from source than
usual. Theyre mostly intended for server environments and as such
contain few GUI applications.</para>
</listitem>
</itemizedlist>
To see what channels are available, go to <link
xlink:href="https://nixos.org/channels"/>. (Note that the URIs of the
various channels redirect to a directory that contains the channels
latest version and includes ISO images and VirtualBox
appliances.)</para>
<para>When you first install NixOS, youre automatically subscribed to
the NixOS channel that corresponds to your installation source. For
instance, if you installed from a 17.03 ISO, you will be subscribed to
the <literal>nixos-17.03</literal> channel. To see which NixOS
channel youre subscribed to, run the following as root:
or
<literal
xlink:href="https://nixos.org/channels/nixos-unstable-small">nixos-unstable-small</literal>.
These are identical to the stable and unstable channels described above,
except that they contain fewer binary packages. This means they get
updated faster than the regular channels (for instance, when a critical
security patch is committed to NixOSs source tree), but may require
more packages to be built from source than usual. Theyre mostly
intended for server environments and as such contain few GUI applications.
</para>
</listitem>
</itemizedlist>
To see what channels are available, go to
<link
xlink:href="https://nixos.org/channels"/>. (Note that the URIs of the
various channels redirect to a directory that contains the channels latest
version and includes ISO images and VirtualBox appliances.)
</para>
<para>
When you first install NixOS, youre automatically subscribed to the NixOS
channel that corresponds to your installation source. For instance, if you
installed from a 17.03 ISO, you will be subscribed to the
<literal>nixos-17.03</literal> channel. To see which NixOS channel youre
subscribed to, run the following as root:
<screen>
# nix-channel --list | grep nixos
nixos https://nixos.org/channels/nixos-unstable
</screen>
To switch to a different NixOS channel, do
To switch to a different NixOS channel, do
<screen>
# nix-channel --add https://nixos.org/channels/<replaceable>channel-name</replaceable> nixos
</screen>
(Be sure to include the <literal>nixos</literal> parameter at the
end.) For instance, to use the NixOS 17.03 stable channel:
(Be sure to include the <literal>nixos</literal> parameter at the end.) For
instance, to use the NixOS 17.03 stable channel:
<screen>
# nix-channel --add https://nixos.org/channels/nixos-17.03 nixos
</screen>
If you have a server, you may want to use the “small” channel instead:
If you have a server, you may want to use the “small” channel instead:
<screen>
# nix-channel --add https://nixos.org/channels/nixos-17.03-small nixos
</screen>
And if you want to live on the bleeding edge:
And if you want to live on the bleeding edge:
<screen>
# nix-channel --add https://nixos.org/channels/nixos-unstable nixos
</screen>
</para>
<para>You can then upgrade NixOS to the latest version in your chosen
channel by running
</para>
<para>
You can then upgrade NixOS to the latest version in your chosen channel by
running
<screen>
# nixos-rebuild switch --upgrade
</screen>
which is equivalent to the more verbose <literal>nix-channel --update nixos;
nixos-rebuild switch</literal>.
</para>
<note>
<para>
Channels are set per user. This means that running <literal> nix-channel
--add</literal> as a non root user (or without sudo) will not affect
configuration in <literal>/etc/nixos/configuration.nix</literal>
</para>
</note>
<warning>
<para>
It is generally safe to switch back and forth between channels. The only
exception is that a newer NixOS may also have a newer Nix version, which may
involve an upgrade of Nixs database schema. This cannot be undone easily,
so in that case you will not be able to go back to your original channel.
</para>
</warning>
<section>
<title>Automatic Upgrades</title>
which is equivalent to the more verbose <literal>nix-channel --update
nixos; nixos-rebuild switch</literal>.</para>
<note><para>Channels are set per user. This means that running <literal>
nix-channel --add</literal> as a non root user (or without sudo) will not
affect configuration in <literal>/etc/nixos/configuration.nix</literal>
</para></note>
<warning><para>It is generally safe to switch back and forth between
channels. The only exception is that a newer NixOS may also have a
newer Nix version, which may involve an upgrade of Nixs database
schema. This cannot be undone easily, so in that case you will not be
able to go back to your original channel.</para></warning>
<section><title>Automatic Upgrades</title>
<para>You can keep a NixOS system up-to-date automatically by adding
the following to <filename>configuration.nix</filename>:
<para>
You can keep a NixOS system up-to-date automatically by adding the following
to <filename>configuration.nix</filename>:
<programlisting>
<xref linkend="opt-system.autoUpgrade.enable"/> = true;
</programlisting>
This enables a periodically executed systemd service named
<literal>nixos-upgrade.service</literal>. It runs
<command>nixos-rebuild switch --upgrade</command> to upgrade NixOS to
the latest version in the current channel. (To see when the service
runs, see <command>systemctl list-timers</command>.) You can also
specify a channel explicitly, e.g.
This enables a periodically executed systemd service named
<literal>nixos-upgrade.service</literal>. It runs <command>nixos-rebuild
switch --upgrade</command> to upgrade NixOS to the latest version in the
current channel. (To see when the service runs, see <command>systemctl
list-timers</command>.) You can also specify a channel explicitly, e.g.
<programlisting>
<xref linkend="opt-system.autoUpgrade.channel"/> = https://nixos.org/channels/nixos-17.03;
</programlisting>
</para>
</section>
</para>
</section>
</chapter>