systemd/man/sysupdate.features.xml

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  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="sysupdate.features" conditional='ENABLE_SYSUPDATE'
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sysupdate.features</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sysupdate.features</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sysupdate.features</refname>
    <refpurpose>Definition Files for Optional Features</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><simplelist>
      <member><filename>/etc/sysupdate.d/*.feature</filename></member>
      <member><filename>/run/sysupdate.d/*.feature</filename></member>
      <member><filename>/usr/local/lib/sysupdate.d/*.feature</filename></member>
      <member><filename>/usr/lib/sysupdate.d/*.feature</filename></member>
    </simplelist></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>"Optional Features" are functionality provided by
    <citerefentry><refentrytitle>systemd-sysupdate</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
    that allow a distribution to define sets of
    <citerefentry><refentrytitle>sysupdate.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    transfer definitions that are intended to be enabled or disabled by the system administrator.</para>

    <para>When a feature is enabled, transfers belonging to it will be considered when checking for and
    downloading updates, when vacuuming, and in all other situations.
    In effect, transfers belonging to a feature will always be updated in lock-step with the rest of their
    target.
    This is the primary difference an Optional Feature and a <command>systemd-sysupdate</command> component.
    When a feature is disabled, its transfers will not be considered when checking for and downloading updates,
    but <command>systemd-sysupdate</command> will still consider them while vacuuming and in other situations
    where it needs to determine ownership over previously downloaded system resources.
    <command>systemd-sysupdate</command> will clean up all instances of the feature's transfers whenever it
    is disabled, effectively uninstalling it.</para>

    <para>Optional Features are described by <filename>sysupdate.d/*.feature</filename> files, which are
    defined below.
    Transfers can declare that they belong to a feature via the <varname>Features=</varname> setting.
    Feature definitions support drop-in files, which are most commonly used to override the
    <varname>Enabled=</varname> setting).
    They can also be masked out to hide the availability of the feature entirely.</para>

    <para>Each <filename>*.feature</filename> file contains one section: [Feature].</para>
  </refsect1>

  <refsect1>
    <title>[Feature] Section Options</title>

    <para>This section defines general properties of this feature.</para>

    <variablelist>
      <varlistentry>
        <term><varname>Description=</varname></term>

        <listitem><para>A short human readable description of this feature.
        This may be used as a label for this feature, so the string should meaningfully identify the feature
        among the features available in <filename>sysupdate.d/</filename>.</para>

        <xi:include href="version-info.xml" xpointer="v257"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Documentation=</varname></term>

        <listitem><para>A user-presentable URL to documentation about this feature.
        This setting supports specifier expansion; see below for details on supported specifiers.</para>

        <xi:include href="version-info.xml" xpointer="v257"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>AppStream=</varname></term>

        <listitem><para>A URL to an
        <ulink url="https://www.freedesktop.org/software/appstream/docs/chap-CatalogData.html">AppStream catalog</ulink>
        XML file.
        This may be used by software centers (such as GNOME Software or KDE Discover) to present rich
        metadata about this feature.
        This includes display names, chagnelogs, icons, and more.
        This setting supports specifier expansion; see below for details on supported specifiers.</para>

        <xi:include href="version-info.xml" xpointer="v257"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Enabled=</varname></term>

        <listitem><para>Whether or not this feature is enabled. If unspecified, the feature is disabled
        by default.</para>

        <xi:include href="version-info.xml" xpointer="v257"/></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Specifiers</title>

    <para>Specifiers may be used in the <varname>Documentation=</varname> and <varname>AppStream=</varname>
    settings. The following expansions are understood:</para>

    <table class='specifiers'>
      <title>Specifiers available</title>
      <tgroup cols='3' align='left' colsep='1' rowsep='1'>
        <colspec colname="spec" />
        <colspec colname="mean" />
        <colspec colname="detail" />
        <thead>
          <row>
            <entry>Specifier</entry>
            <entry>Meaning</entry>
            <entry>Details</entry>
          </row>
        </thead>
        <tbody>
          <xi:include href="standard-specifiers.xml" xpointer="a"/>
          <xi:include href="standard-specifiers.xml" xpointer="A"/>
          <xi:include href="standard-specifiers.xml" xpointer="b"/>
          <xi:include href="standard-specifiers.xml" xpointer="B"/>
          <xi:include href="standard-specifiers.xml" xpointer="H"/>
          <xi:include href="standard-specifiers.xml" xpointer="l"/>
          <xi:include href="standard-specifiers.xml" xpointer="m"/>
          <xi:include href="standard-specifiers.xml" xpointer="M"/>
          <xi:include href="standard-specifiers.xml" xpointer="o"/>
          <xi:include href="standard-specifiers.xml" xpointer="v"/>
          <xi:include href="standard-specifiers.xml" xpointer="w"/>
          <xi:include href="standard-specifiers.xml" xpointer="W"/>
          <xi:include href="standard-specifiers.xml" xpointer="T"/>
          <xi:include href="standard-specifiers.xml" xpointer="V"/>
          <xi:include href="standard-specifiers.xml" xpointer="percent"/>
        </tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Development Tools for Image-Based OS</title>

      <para>We'll use the hypothetical "foobarOS" described in
      <citerefentry><refentrytitle>sysupdate.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> as our
      example base OS.
      The vast majority of foobarOS's users have no need for a compiler, build system, debugger, and other
      such development tools to be part of their OS.
      However, the developers of foobarOS itself need this build tooling to be available.
      So, foobarOS needs to provide a system extension image (see
      <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry>)
      containing these development tools, and this image must be updated in lock-step with the underlying
      base OS.
      This is a great use case for an optional OS feature, so let's define one:
      </para>

      <para><programlisting># /usr/lib/sysupdate.d/devel.feature
[Feature]
Description=Development Tools
Documentation=https://developer.example.com/foobarOS/getting-started
Enabled=false
</programlisting></para>

      <para>The above defines the <literal>devel</literal> feature, and disables it by default.
      Now let's a define a transfer that's associated with this feature:</para>

      <para><programlisting># /usr/lib/sysupdate.d/50-devel.transfer
[Transfer]
Features=devel
ProtectVersion=%A

[Source]
Type=url-file
Path=https://download.example.com/
MatchPattern=foobarOS_@v_devel.raw.xz

[Target]
Type=regular-file
Path=/var/lib/extensions
MatchPattern=foobarOS_@v_devel.raw
Mode=0444
InstancesMax=2
</programlisting></para>

      <para>With these two files, we have created a feature called <literal>devel</literal> that, when
      enabled, will download and decompress the appropriate version of
      <literal>https://download.example.com/foobarOS_@v_devel.raw.xz</literal> into
      <literal>/var/lib/extensions/foobarOS_@v_devel.raw</literal> during each OS update.</para>

      <para>The developers of foobarOS can enable the <literal>devel</literal> feature on their workstations
      by creating the following drop-in:</para>

      <para><programlisting># /etc/sysupdate.d/devel.feature.d/enable.conf
[Feature]
Enabled=true
</programlisting></para>
    </example>

    <example>
      <title>Proprietary Drivers</title>

      <para>Suppose that many of foobarOS's users have a GPU manufactured by the MVISUAL corporation.
      Due to lack of documentation and difficulty in reverse-engineering the hardware, the open-source
      drivers for MVISUAL GPUs are unable to make proper use of available graphics and compute performance.
      MVISUAL provides a redistributable proprietary driver for their cards, and foobarOS's developers
      distribute them to address their users' needs.</para>

      <para>MVISUAL's driver has a couple different parts that must be installed for it to function: a UKI
      addon to configure the kernel command-line, an initrd system extension image to add the MVISUAL kernel
      module into the initrd, and a regular system extension image to add the proprietary OpenGL and Vulkan
      userspace drivers.
      All of these should be version-locked to the core OS.</para>

      <para>Let's start by defining an optional feature named <literal>mvisual-driver</literal>:</para>

      <para><programlisting># /usr/lib/sysupdate.d/mvisual-driver.feature
[Feature]
Description=MVISUAL Proprietary GPU Driver
Documentation=https://support.example.com/foobarOS/mvisual
AppStream=https://metadata.example.com/mvisual-driver-%A.xml.gz
</programlisting></para>

      <para>Note that we define AppStream metadata for this feature, because we want software centers to
      present it to end-users.
      Next, let's define the corresponding transfers:</para>

      <para><programlisting># /usr/lib/sysupdate.d/50-mvisual-userspace.transfer
[Transfer]
Features=mvisual-driver
ProtectVersion=%A

[Source]
Type=url-file
Path=https://download.example.com/
MatchPattern=foobarOS_@v_mvisual_userspace.raw.xz

[Target]
Type=regular-file
Path=/var/lib/extensions
MatchPattern=foobarOS_@v_mvisual.raw
Mode=0444
InstancesMax=2
</programlisting></para>

      <para><programlisting># /usr/lib/sysupdate.d/70-mvisual-initrd.transfer
[Transfer]
Features=mvisual-driver
ProtectVersion=%A

[Source]
Type=url-file
Path=https://download.example.com/
MatchPattern=foobarOS_@v_mvisual_initrd.raw.xz

[Target]
Type=regular-file
Path=/EFI/Linux
PathRelativeTo=boot
MatchPattern=foobarOS_@v.efi.extra.d/foobarOS_mvisual.raw
Mode=0444
InstancesMax=2
</programlisting></para>

      <para><programlisting># /usr/lib/sysupdate.d/90-mvisual-addon.transfer
[Transfer]
Features=mvisual-driver
ProtectVersion=%A

[Source]
Type=url-file
Path=https://download.example.com/
MatchPattern=foobarOS_@v_mvisual_addon.efi.xz

[Target]
Type=regular-file
Path=/EFI/Linux
PathRelativeTo=boot
MatchPattern=foobarOS_@v.efi.extra.d/foobarOS_mvisual.addon.efi
Mode=0444
InstancesMax=2
</programlisting></para>
    </example>

    <example>
      <title>Intersecting Features</title>

      <para>Suppose that MVISUAL releases special tooling to help a distribution developer troubleshoot
      crashes in their proprietary driver.
      Let's define a transfer:</para>

      <para><programlisting># /usr/lib/sysupdate.d/50-mvisual-debugger.transfer
[Transfer]
RequisiteFeatures=devel mvisual-driver
ProtectVersion=%A

[Source]
Type=url-file
Path=https://download.example.com/
MatchPattern=foobarOS_@v_devel.raw.xz

[Target]
Type=regular-file
Path=/var/lib/extensions
MatchPattern=foobarOS_@v_devel.raw
Mode=0444
InstancesMax=2
</programlisting></para>

      <para>This transfer will be used only if both the <literal>devel</literal> and
      <literal>mvisual-driver</literal> features are enabled.</para>
    </example>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-sysupdate</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sysupdate.d</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>