Merge pull request #129154 from bobby285271/pr15

nixos/doc: convert Chapter 1, 3, 4 to CommonMark

10 files changed, 564 insertions, 293 deletions

diff --git a/nixos/doc/manual/from_md/installation/changing-config.chapter.xml b/nixos/doc/manual/from_md/installation/changing-config.chapter.xml
new file mode 100644
index 00000000000..86f0b15b41c
--- /dev/null
+++ b/nixos/doc/manual/from_md/installation/changing-config.chapter.xml
@@ -0,0 +1,117 @@
+<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-changing-config">
+  <title>Changing the Configuration</title>
+  <para>
+    The file <literal>/etc/nixos/configuration.nix</literal> contains
+    the current configuration of your machine. Whenever you’ve
+    <link linkend="ch-configuration">changed something</link> in that
+    file, you should do
+  </para>
+  <programlisting>
+# nixos-rebuild switch
+</programlisting>
+  <para>
+    to build the new configuration, make it the default configuration
+    for booting, and try to realise the configuration in the running
+    system (e.g., by restarting system services).
+  </para>
+  <warning>
+    <para>
+      This command doesn't start/stop
+      <link linkend="opt-systemd.user.services">user services</link>
+      automatically. <literal>nixos-rebuild</literal> only runs a
+      <literal>daemon-reload</literal> for each user with running user
+      services.
+    </para>
+  </warning>
+  <warning>
+    <para>
+      These commands must be executed as root, so you should either run
+      them from a root shell or by prefixing them with
+      <literal>sudo -i</literal>.
+    </para>
+  </warning>
+  <para>
+    You can also do
+  </para>
+  <programlisting>
+# nixos-rebuild test
+</programlisting>
+  <para>
+    to build the configuration and switch the running system to it, but
+    without making it the boot default. So if (say) the configuration
+    locks up your machine, you can just reboot to get back to a working
+    configuration.
+  </para>
+  <para>
+    There is also
+  </para>
+  <programlisting>
+# nixos-rebuild boot
+</programlisting>
+  <para>
+    to build the configuration and make it the boot default, but not
+    switch to it now (so it will only take effect after the next
+    reboot).
+  </para>
+  <para>
+    You can make your configuration show up in a different submenu of
+    the GRUB 2 boot screen by giving it a different <emphasis>profile
+    name</emphasis>, e.g.
+  </para>
+  <programlisting>
+# nixos-rebuild switch -p test
+</programlisting>
+  <para>
+    which causes the new configuration (and previous ones created using
+    <literal>-p test</literal>) to show up in the GRUB submenu
+    <quote>NixOS - Profile 'test'</quote>. This can be useful to
+    separate test configurations from <quote>stable</quote>
+    configurations.
+  </para>
+  <para>
+    Finally, you can do
+  </para>
+  <programlisting>
+$ nixos-rebuild build
+</programlisting>
+  <para>
+    to build the configuration but nothing more. This is useful to see
+    whether everything compiles cleanly.
+  </para>
+  <para>
+    If you have a machine that supports hardware virtualisation, you can
+    also test the new configuration in a sandbox by building and running
+    a QEMU <emphasis>virtual machine</emphasis> that contains the
+    desired configuration. Just do
+  </para>
+  <programlisting>
+$ nixos-rebuild build-vm
+$ ./result/bin/run-*-vm
+</programlisting>
+  <para>
+    The VM does not have any data from your host system, so your
+    existing user accounts and home directories will not be available
+    unless you have set <literal>mutableUsers = false</literal>. Another
+    way is to temporarily add the following to your configuration:
+  </para>
+  <programlisting language="bash">
+users.users.your-user.initialHashedPassword = &quot;test&quot;;
+</programlisting>
+  <para>
+    <emphasis>Important:</emphasis> delete the $hostname.qcow2 file if
+    you have started the virtual machine at least once without the right
+    users, otherwise the changes will not get picked up. You can forward
+    ports on the host to the guest. For instance, the following will
+    forward host port 2222 to guest port 22 (SSH):
+  </para>
+  <programlisting>
+$ QEMU_NET_OPTS=&quot;hostfwd=tcp::2222-:22&quot; ./result/bin/run-*-vm
+</programlisting>
+  <para>
+    allowing you to log in via SSH (assuming you have set the
+    appropriate passwords or SSH authorized keys):
+  </para>
+  <programlisting>
+$ ssh -p 2222 localhost
+</programlisting>
+</chapter>
diff --git a/nixos/doc/manual/from_md/installation/obtaining.chapter.xml b/nixos/doc/manual/from_md/installation/obtaining.chapter.xml
new file mode 100644
index 00000000000..a922feda253
--- /dev/null
+++ b/nixos/doc/manual/from_md/installation/obtaining.chapter.xml
@@ -0,0 +1,48 @@
+<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-obtaining">
+  <title>Obtaining NixOS</title>
+  <para>
+    NixOS ISO images can be downloaded from the
+    <link xlink:href="https://nixos.org/nixos/download.html">NixOS
+    download page</link>. There are a number of installation options. If
+    you happen to have an optical drive and a spare CD, burning the
+    image to CD and booting from that is probably the easiest option.
+    Most people will need to prepare a USB stick to boot from.
+    <xref linkend="sec-booting-from-usb" /> describes the preferred
+    method to prepare a USB stick. A number of alternative methods are
+    presented in the
+    <link xlink:href="https://nixos.wiki/wiki/NixOS_Installation_Guide#Making_the_installation_media">NixOS
+    Wiki</link>.
+  </para>
+  <para>
+    As an alternative to installing NixOS yourself, you can get a
+    running NixOS system through several other means:
+  </para>
+  <itemizedlist>
+    <listitem>
+      <para>
+        Using virtual appliances in Open Virtualization Format (OVF)
+        that can be imported into VirtualBox. These are available from
+        the
+        <link xlink:href="https://nixos.org/nixos/download.html">NixOS
+        download page</link>.
+      </para>
+    </listitem>
+    <listitem>
+      <para>
+        Using AMIs for Amazon’s EC2. To find one for your region and
+        instance type, please refer to the
+        <link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/ec2-amis.nix">list
+        of most recent AMIs</link>.
+      </para>
+    </listitem>
+    <listitem>
+      <para>
+        Using NixOps, the NixOS-based cloud deployment tool, which
+        allows you to provision VirtualBox and EC2 NixOS instances from
+        declarative specifications. Check out the
+        <link xlink:href="https://nixos.org/nixops">NixOps
+        homepage</link> for details.
+      </para>
+    </listitem>
+  </itemizedlist>
+</chapter>
diff --git a/nixos/doc/manual/from_md/installation/upgrading.chapter.xml b/nixos/doc/manual/from_md/installation/upgrading.chapter.xml
new file mode 100644
index 00000000000..c0c5a2190fb
--- /dev/null
+++ b/nixos/doc/manual/from_md/installation/upgrading.chapter.xml
@@ -0,0 +1,152 @@
+<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" 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 NixOS’s Git
+    repository after certain tests have passed and all packages have
+    been built. These channels are:
+  </para>
+  <itemizedlist>
+    <listitem>
+      <para>
+        <emphasis>Stable channels</emphasis>, such as
+        <link xlink:href="https://nixos.org/channels/nixos-21.05"><literal>nixos-21.05</literal></link>.
+        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 4.19.34 to 4.19.38 (a minor bug fix),
+        but not from 4.19.x to 4.20.x (a major change that has the
+        potential to break things). Stable channels are generally
+        maintained until the next stable branch is created.
+      </para>
+    </listitem>
+    <listitem>
+      <para>
+        The <emphasis>unstable channel</emphasis>,
+        <link xlink:href="https://nixos.org/channels/nixos-unstable"><literal>nixos-unstable</literal></link>.
+        This corresponds to NixOS’s main development branch, and may
+        thus see radical changes between channel updates. It’s not
+        recommended for production systems.
+      </para>
+    </listitem>
+    <listitem>
+      <para>
+        <emphasis>Small channels</emphasis>, such as
+        <link xlink:href="https://nixos.org/channels/nixos-21.05-small"><literal>nixos-21.05-small</literal></link>
+        or
+        <link xlink:href="https://nixos.org/channels/nixos-unstable-small"><literal>nixos-unstable-small</literal></link>.
+        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
+        NixOS’s source tree), but may require more packages to be built
+        from source than usual. They’re mostly intended for server
+        environments and as such contain few GUI applications.
+      </para>
+    </listitem>
+  </itemizedlist>
+  <para>
+    To see what channels are available, go to
+    <link xlink:href="https://nixos.org/channels">https://nixos.org/channels</link>.
+    (Note that the URIs of the various channels redirect to a directory
+    that contains the channel’s latest version and includes ISO images
+    and VirtualBox appliances.) Please note that during the release
+    process, channels that are not yet released will be present here as
+    well. See the Getting NixOS page
+    <link xlink:href="https://nixos.org/nixos/download.html">https://nixos.org/nixos/download.html</link>
+    to find the newest supported stable release.
+  </para>
+  <para>
+    When you first install NixOS, you’re automatically subscribed to the
+    NixOS channel that corresponds to your installation source. For
+    instance, if you installed from a 21.05 ISO, you will be subscribed
+    to the <literal>nixos-21.05</literal> channel. To see which NixOS
+    channel you’re subscribed to, run the following as root:
+  </para>
+  <programlisting>
+# nix-channel --list | grep nixos
+nixos https://nixos.org/channels/nixos-unstable
+</programlisting>
+  <para>
+    To switch to a different NixOS channel, do
+  </para>
+  <programlisting>
+# nix-channel --add https://nixos.org/channels/channel-name nixos
+</programlisting>
+  <para>
+    (Be sure to include the <literal>nixos</literal> parameter at the
+    end.) For instance, to use the NixOS 21.05 stable channel:
+  </para>
+  <programlisting>
+# nix-channel --add https://nixos.org/channels/nixos-21.05 nixos
+</programlisting>
+  <para>
+    If you have a server, you may want to use the <quote>small</quote>
+    channel instead:
+  </para>
+  <programlisting>
+# nix-channel --add https://nixos.org/channels/nixos-21.05-small nixos
+</programlisting>
+  <para>
+    And if you want to live on the bleeding edge:
+  </para>
+  <programlisting>
+# nix-channel --add https://nixos.org/channels/nixos-unstable nixos
+</programlisting>
+  <para>
+    You can then upgrade NixOS to the latest version in your chosen
+    channel by running
+  </para>
+  <programlisting>
+# nixos-rebuild switch --upgrade
+</programlisting>
+  <para>
+    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 Nix’s 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 xml:id="sec-upgrading-automatic">
+    <title>Automatic Upgrades</title>
+    <para>
+      You can keep a NixOS system up-to-date automatically by adding the
+      following to <literal>configuration.nix</literal>:
+    </para>
+    <programlisting language="bash">
+system.autoUpgrade.enable = true;
+system.autoUpgrade.allowReboot = true;
+</programlisting>
+    <para>
+      This enables a periodically executed systemd service named
+      <literal>nixos-upgrade.service</literal>. If the
+      <literal>allowReboot</literal> option is <literal>false</literal>,
+      it runs <literal>nixos-rebuild switch --upgrade</literal> to
+      upgrade NixOS to the latest version in the current channel. (To
+      see when the service runs, see
+      <literal>systemctl list-timers</literal>.) If
+      <literal>allowReboot</literal> is <literal>true</literal>, then
+      the system will automatically reboot if the new generation
+      contains a different kernel, initrd or kernel modules. You can
+      also specify a channel explicitly, e.g.
+    </para>
+    <programlisting language="bash">
+system.autoUpgrade.channel = https://nixos.org/channels/nixos-21.05;
+</programlisting>
+  </section>
+</chapter>
diff --git a/nixos/doc/manual/installation/changing-config.chapter.md b/nixos/doc/manual/installation/changing-config.chapter.md
new file mode 100644
index 00000000000..8a404f085d7
--- /dev/null
+++ b/nixos/doc/manual/installation/changing-config.chapter.md
@@ -0,0 +1,100 @@
+# Changing the Configuration {#sec-changing-config}
+
+The file `/etc/nixos/configuration.nix` contains the current
+configuration of your machine. Whenever you've [changed
+something](#ch-configuration) in that file, you should do
+
+```ShellSession
+# nixos-rebuild switch
+```
+
+to build the new configuration, make it the default configuration for
+booting, and try to realise the configuration in the running system
+(e.g., by restarting system services).
+
+::: {.warning}
+This command doesn\'t start/stop [user services](#opt-systemd.user.services)
+automatically. `nixos-rebuild` only runs a `daemon-reload` for each user with running
+user services.
+:::
+
+::: {.warning}
+These commands must be executed as root, so you should either run them
+from a root shell or by prefixing them with `sudo -i`.
+:::
+
+You can also do
+
+```ShellSession
+# nixos-rebuild test
+```
+
+to build the configuration and switch the running system to it, but
+without making it the boot default. So if (say) the configuration locks
+up your machine, you can just reboot to get back to a working
+configuration.
+
+There is also
+
+```ShellSession
+# nixos-rebuild boot
+```
+
+to build the configuration and make it the boot default, but not switch
+to it now (so it will only take effect after the next reboot).
+
+You can make your configuration show up in a different submenu of the
+GRUB 2 boot screen by giving it a different *profile name*, e.g.
+
+```ShellSession
+# nixos-rebuild switch -p test
+```
+
+which causes the new configuration (and previous ones created using
+`-p test`) to show up in the GRUB submenu "NixOS - Profile \'test\'".
+This can be useful to separate test configurations from "stable"
+configurations.
+
+Finally, you can do
+
+```ShellSession
+$ nixos-rebuild build
+```
+
+to build the configuration but nothing more. This is useful to see
+whether everything compiles cleanly.
+
+If you have a machine that supports hardware virtualisation, you can
+also test the new configuration in a sandbox by building and running a
+QEMU *virtual machine* that contains the desired configuration. Just do
+
+```ShellSession
+$ nixos-rebuild build-vm
+$ ./result/bin/run-*-vm
+```
+
+The VM does not have any data from your host system, so your existing
+user accounts and home directories will not be available unless you have
+set `mutableUsers = false`. Another way is to temporarily add the
+following to your configuration:
+
+```nix
+users.users.your-user.initialHashedPassword = "test";
+```
+
+*Important:* delete the \$hostname.qcow2 file if you have started the
+virtual machine at least once without the right users, otherwise the
+changes will not get picked up. You can forward ports on the host to the
+guest. For instance, the following will forward host port 2222 to guest
+port 22 (SSH):
+
+```ShellSession
+$ QEMU_NET_OPTS="hostfwd=tcp::2222-:22" ./result/bin/run-*-vm
+```
+
+allowing you to log in via SSH (assuming you have set the appropriate
+passwords or SSH authorized keys):
+
+```ShellSession
+$ ssh -p 2222 localhost
+```
diff --git a/nixos/doc/manual/installation/changing-config.xml b/nixos/doc/manual/installation/changing-config.xml
deleted file mode 100644
index 4288806d5eb..00000000000
--- a/nixos/doc/manual/installation/changing-config.xml
+++ /dev/null
@@ -1,97 +0,0 @@
-<chapter xmlns="http://docbook.org/ns/docbook"
-         xmlns:xlink="http://www.w3.org/1999/xlink"
-         version="5.0"
-         xml:id="sec-changing-config">
- <title>Changing the Configuration</title>
- <para>
-  The file <filename>/etc/nixos/configuration.nix</filename> contains the
-  current configuration of your machine. Whenever you’ve
-  <link linkend="ch-configuration">changed something</link> in that file, you
-  should do
-<screen>
-<prompt># </prompt>nixos-rebuild switch
-</screen>
-  to build the new configuration, make it the default configuration for
-  booting, and try to realise the configuration in the running system (e.g., by
-  restarting system services).
-  <warning>
-   <para>
-    This command doesn't start/stop <link linkend="opt-systemd.user.services">user
-    services</link> automatically. <command>nixos-rebuild</command> only runs a
-    <literal>daemon-reload</literal> for each user with running user services.
-   </para>
-  </warning>
- </para>
- <warning>
-  <para>
-   These commands must be executed as root, so you should either run them from
-   a root shell or by prefixing them with <literal>sudo -i</literal>.
-  </para>
- </warning>
- <para>
-  You can also do
-<screen>
-<prompt># </prompt>nixos-rebuild test
-</screen>
-  to build the configuration and switch the running system to it, but without
-  making it the boot default. So if (say) the configuration locks up your
-  machine, you can just reboot to get back to a working configuration.
- </para>
- <para>
-  There is also
-<screen>
-<prompt># </prompt>nixos-rebuild boot
-</screen>
-  to build the configuration and make it the boot default, but not switch to it
-  now (so it will only take effect after the next reboot).
- </para>
- <para>
-  You can make your configuration show up in a different submenu of the GRUB 2
-  boot screen by giving it a different <emphasis>profile name</emphasis>, e.g.
-<screen>
-<prompt># </prompt>nixos-rebuild switch -p test
-</screen>
-  which causes the new configuration (and previous ones created using
-  <literal>-p test</literal>) to show up in the GRUB submenu “NixOS - Profile
-  'test'”. This can be useful to separate test configurations from
-  “stable” configurations.
- </para>
- <para>
-  Finally, you can do
-<screen>
-<prompt>$ </prompt>nixos-rebuild build
-</screen>
-  to build the configuration but nothing more. This is useful to see whether
-  everything compiles cleanly.
- </para>
- <para>
-  If you have a machine that supports hardware virtualisation, you can also
-  test the new configuration in a sandbox by building and running a QEMU
-  <emphasis>virtual machine</emphasis> that contains the desired configuration.
-  Just do
-<screen>
-<prompt>$ </prompt>nixos-rebuild build-vm
-<prompt>$ </prompt>./result/bin/run-*-vm
-</screen>
-  The VM does not have any data from your host system, so your existing user
-  accounts and home directories will not be available unless you have set
-  <literal>mutableUsers = false</literal>. Another way is to temporarily add
-  the following to your configuration:
-<screen>
-<link linkend="opt-users.users._name_.initialHashedPassword">users.users.your-user.initialHashedPassword</link> = "test";
-</screen>
-  <emphasis>Important:</emphasis> delete the $hostname.qcow2 file if you have
-  started the virtual machine at least once without the right users, otherwise
-  the changes will not get picked up. You can forward ports on the host to the
-  guest. For instance, the following will forward host port 2222 to guest port
-  22 (SSH):
-<screen>
-<prompt>$ </prompt>QEMU_NET_OPTS="hostfwd=tcp::2222-:22" ./result/bin/run-*-vm
-</screen>
-  allowing you to log in via SSH (assuming you have set the appropriate
-  passwords or SSH authorized keys):
-<screen>
-<prompt>$ </prompt>ssh -p 2222 localhost
-</screen>
- </para>
-</chapter>
diff --git a/nixos/doc/manual/installation/installation.xml b/nixos/doc/manual/installation/installation.xml
index 2901f462dee..cc18a9c6e9f 100644
--- a/nixos/doc/manual/installation/installation.xml
+++ b/nixos/doc/manual/installation/installation.xml
@@ -10,8 +10,8 @@
    first-time use.
   </para>
  </partintro>
- <xi:include href="obtaining.xml" />
+ <xi:include href="../from_md/installation/obtaining.chapter.xml" />
  <xi:include href="installing.xml" />
- <xi:include href="changing-config.xml" />
- <xi:include href="upgrading.xml" />
+ <xi:include href="../from_md/installation/changing-config.chapter.xml" />
+ <xi:include href="../from_md/installation/upgrading.chapter.xml" />
 </part>
diff --git a/nixos/doc/manual/installation/obtaining.chapter.md b/nixos/doc/manual/installation/obtaining.chapter.md
new file mode 100644
index 00000000000..832ec6146a9
--- /dev/null
+++ b/nixos/doc/manual/installation/obtaining.chapter.md
@@ -0,0 +1,26 @@
+# Obtaining NixOS {#sec-obtaining}
+
+NixOS ISO images can be downloaded from the [NixOS download
+page](https://nixos.org/nixos/download.html). There are a number of
+installation options. If you happen to have an optical drive and a spare
+CD, burning the image to CD and booting from that is probably the
+easiest option. Most people will need to prepare a USB stick to boot
+from. [](#sec-booting-from-usb) describes the preferred method to
+prepare a USB stick. A number of alternative methods are presented in
+the [NixOS Wiki](https://nixos.wiki/wiki/NixOS_Installation_Guide#Making_the_installation_media).
+
+As an alternative to installing NixOS yourself, you can get a running
+NixOS system through several other means:
+
+-   Using virtual appliances in Open Virtualization Format (OVF) that
+    can be imported into VirtualBox. These are available from the [NixOS
+    download page](https://nixos.org/nixos/download.html).
+
+-   Using AMIs for Amazon's EC2. To find one for your region and
+    instance type, please refer to the [list of most recent
+    AMIs](https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/ec2-amis.nix).
+
+-   Using NixOps, the NixOS-based cloud deployment tool, which allows
+    you to provision VirtualBox and EC2 NixOS instances from declarative
+    specifications. Check out the [NixOps
+    homepage](https://nixos.org/nixops) for details.
diff --git a/nixos/doc/manual/installation/obtaining.xml b/nixos/doc/manual/installation/obtaining.xml
deleted file mode 100644
index 3b8671782de..00000000000
--- a/nixos/doc/manual/installation/obtaining.xml
+++ /dev/null
@@ -1,54 +0,0 @@
-<chapter xmlns="http://docbook.org/ns/docbook"
-         xmlns:xlink="http://www.w3.org/1999/xlink"
-         xmlns:xi="http://www.w3.org/2001/XInclude"
-         version="5.0"
-         xml:id="sec-obtaining">
- <title>Obtaining NixOS</title>
- <para>
-  NixOS ISO images can be downloaded from the
-  <link
-xlink:href="https://nixos.org/nixos/download.html">NixOS download
-  page</link>. There are a number of installation options. If you happen to
-  have an optical drive and a spare CD, burning the image to CD and booting
-  from that is probably the easiest option. Most people will need to prepare a
-  USB stick to boot from. <xref linkend="sec-booting-from-usb"/> describes the
-  preferred method to prepare a USB stick. A number of alternative methods are
-  presented in the
-  <link
-xlink:href="https://nixos.wiki/wiki/NixOS_Installation_Guide#Making_the_installation_media">NixOS
-  Wiki</link>.
- </para>
- <para>
-  As an alternative to installing NixOS yourself, you can get a running NixOS
-  system through several other means:
-  <itemizedlist>
-   <listitem>
-    <para>
-     Using virtual appliances in Open Virtualization Format (OVF) that can be
-     imported into VirtualBox. These are available from the
-     <link xlink:href="https://nixos.org/nixos/download.html">NixOS download
-     page</link>.
-    </para>
-   </listitem>
-   <listitem>
-    <para>
-     Using AMIs for Amazon’s EC2. To find one for your region and instance
-     type, please refer to the
-     <link
-    xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/ec2-amis.nix">list
-     of most recent AMIs</link>.
-    </para>
-   </listitem>
-   <listitem>
-    <para>
-     Using NixOps, the NixOS-based cloud deployment tool, which allows you to
-     provision VirtualBox and EC2 NixOS instances from declarative
-     specifications. Check out the
-     <link
-    xlink:href="https://nixos.org/nixops">NixOps homepage</link> for
-     details.
-    </para>
-   </listitem>
-  </itemizedlist>
- </para>
-</chapter>
diff --git a/nixos/doc/manual/installation/upgrading.chapter.md b/nixos/doc/manual/installation/upgrading.chapter.md
new file mode 100644
index 00000000000..b7903b9d3cb
--- /dev/null
+++ b/nixos/doc/manual/installation/upgrading.chapter.md
@@ -0,0 +1,118 @@
+# Upgrading NixOS {#sec-upgrading}
+
+The best way to keep your NixOS installation up to date is to use one of
+the NixOS *channels*. A channel is a Nix mechanism for distributing Nix
+expressions and associated binaries. The NixOS channels are updated
+automatically from NixOS's Git repository after certain tests have
+passed and all packages have been built. These channels are:
+
+-   *Stable channels*, such as [`nixos-21.05`](https://nixos.org/channels/nixos-21.05).
+    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 4.19.34 to 4.19.38 (a minor bug fix), but not
+    from 4.19.x to 4.20.x (a major change that has the potential to break things).
+    Stable channels are generally maintained until the next stable
+    branch is created.
+
+-   The *unstable channel*, [`nixos-unstable`](https://nixos.org/channels/nixos-unstable).
+    This corresponds to NixOS's main development branch, and may thus see
+    radical changes between channel updates. It's not recommended for
+    production systems.
+
+-   *Small channels*, such as [`nixos-21.05-small`](https://nixos.org/channels/nixos-21.05-small)
+    or [`nixos-unstable-small`](https://nixos.org/channels/nixos-unstable-small).
+    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 NixOS's source tree), but may require more packages to be
+    built from source than usual. They're mostly intended for server environments
+    and as such contain few GUI applications.
+
+To see what channels are available, go to <https://nixos.org/channels>.
+(Note that the URIs of the various channels redirect to a directory that
+contains the channel's latest version and includes ISO images and
+VirtualBox appliances.) Please note that during the release process,
+channels that are not yet released will be present here as well. See the
+Getting NixOS page <https://nixos.org/nixos/download.html> to find the
+newest supported stable release.
+
+When you first install NixOS, you're automatically subscribed to the
+NixOS channel that corresponds to your installation source. For
+instance, if you installed from a 21.05 ISO, you will be subscribed to
+the `nixos-21.05` channel. To see which NixOS channel you're subscribed
+to, run the following as root:
+
+```ShellSession
+# nix-channel --list | grep nixos
+nixos https://nixos.org/channels/nixos-unstable
+```
+
+To switch to a different NixOS channel, do
+
+```ShellSession
+# nix-channel --add https://nixos.org/channels/channel-name nixos
+```
+
+(Be sure to include the `nixos` parameter at the end.) For instance, to
+use the NixOS 21.05 stable channel:
+
+```ShellSession
+# nix-channel --add https://nixos.org/channels/nixos-21.05 nixos
+```
+
+If you have a server, you may want to use the "small" channel instead:
+
+```ShellSession
+# nix-channel --add https://nixos.org/channels/nixos-21.05-small nixos
+```
+
+And if you want to live on the bleeding edge:
+
+```ShellSession
+# nix-channel --add https://nixos.org/channels/nixos-unstable nixos
+```
+
+You can then upgrade NixOS to the latest version in your chosen channel
+by running
+
+```ShellSession
+# nixos-rebuild switch --upgrade
+```
+
+which is equivalent to the more verbose `nix-channel --update nixos; nixos-rebuild switch`.
+
+::: {.note}
+Channels are set per user. This means that running `nix-channel --add`
+as a non root user (or without sudo) will not affect
+configuration in `/etc/nixos/configuration.nix`
+:::
+
+::: {.warning}
+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 Nix's database schema. This cannot be undone
+easily, so in that case you will not be able to go back to your original
+channel.
+:::
+
+## Automatic Upgrades {#sec-upgrading-automatic}
+
+You can keep a NixOS system up-to-date automatically by adding the
+following to `configuration.nix`:
+
+```nix
+system.autoUpgrade.enable = true;
+system.autoUpgrade.allowReboot = true;
+```
+
+This enables a periodically executed systemd service named
+`nixos-upgrade.service`. If the `allowReboot` option is `false`, it runs
+`nixos-rebuild switch --upgrade` to upgrade NixOS to the latest version
+in the current channel. (To see when the service runs, see `systemctl list-timers`.)
+If `allowReboot` is `true`, then the system will automatically reboot if
+the new generation contains a different kernel, initrd or kernel
+modules. You can also specify a channel explicitly, e.g.
+
+```nix
+system.autoUpgrade.channel = https://nixos.org/channels/nixos-21.05;
+```
diff --git a/nixos/doc/manual/installation/upgrading.xml b/nixos/doc/manual/installation/upgrading.xml
deleted file mode 100644
index 960d4fa9a43..00000000000
--- a/nixos/doc/manual/installation/upgrading.xml
+++ /dev/null
@@ -1,139 +0,0 @@
-<chapter xmlns="http://docbook.org/ns/docbook"
-         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 NixOS’s 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-21.05">nixos-21.05</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 4.19.34 to 4.19.38 (a minor bug fix), but not from
-     4.19.<replaceable>x</replaceable> to 4.20.<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
-    xlink:href="https://nixos.org/channels/nixos-unstable">nixos-unstable</literal>.
-     This corresponds to NixOS’s main development branch, and may thus see
-     radical changes between channel updates. It’s not recommended for
-     production systems.
-    </para>
-   </listitem>
-   <listitem>
-    <para>
-     <emphasis>Small channels</emphasis>, such as
-     <literal
-    xlink:href="https://nixos.org/channels/nixos-21.05-small">nixos-21.05-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 NixOS’s source tree), but may require
-     more packages to be built from source than usual. They’re 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 channel’s latest
-  version and includes ISO images and VirtualBox appliances.) Please note that
-  during the release process, channels that are not yet released will be
-  present here as well. See the Getting NixOS page
-  <link xlink:href="https://nixos.org/nixos/download.html"/> to find the newest
-  supported stable release.
- </para>
- <para>
-  When you first install NixOS, you’re automatically subscribed to the NixOS
-  channel that corresponds to your installation source. For instance, if you
-  installed from a 21.05 ISO, you will be subscribed to the
-  <literal>nixos-21.05</literal> channel. To see which NixOS channel you’re
-  subscribed to, run the following as root:
-<screen>
-<prompt># </prompt>nix-channel --list | grep nixos
-nixos https://nixos.org/channels/nixos-unstable
-</screen>
-  To switch to a different NixOS channel, do
-<screen>
-<prompt># </prompt>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 21.05 stable channel:
-<screen>
-<prompt># </prompt>nix-channel --add https://nixos.org/channels/nixos-21.05 nixos
-</screen>
-  If you have a server, you may want to use the “small” channel instead:
-<screen>
-<prompt># </prompt>nix-channel --add https://nixos.org/channels/nixos-21.05-small nixos
-</screen>
-  And if you want to live on the bleeding edge:
-<screen>
-<prompt># </prompt>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
-<screen>
-<prompt># </prompt>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 Nix’s 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 xml:id="sec-upgrading-automatic">
-  <title>Automatic Upgrades</title>
-
-  <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;
-<xref linkend="opt-system.autoUpgrade.allowReboot"/> = true;
-</programlisting>
-   This enables a periodically executed systemd service named
-   <literal>nixos-upgrade.service</literal>. If the <literal>allowReboot</literal>
-   option is <literal>false</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>.)
-   If <literal>allowReboot</literal> is <literal>true</literal>, then the
-   system will automatically reboot if the new generation contains a different
-   kernel, initrd or kernel modules.
-   You can also specify a channel explicitly, e.g.
-<programlisting>
-<xref linkend="opt-system.autoUpgrade.channel"/> = https://nixos.org/channels/nixos-21.05;
-</programlisting>
-  </para>
- </section>
-</chapter>