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https://github.com/systemd/systemd.git
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Daan De Meyer
bb5ec7abd5
GPT limits partition labels to 36 characters. A label built from a partition type identifier uses up most of them: "usr-x86-64-verity-sig" alone takes 21. Only 15 characters remain for a version string or anything else. Accept "-vty" for "-verity", "-vsig" for "-verity-sig", and a "2" suffix for "-secondary" after "root" or "usr". "usr-x86-64-vsig" takes 15 characters, and "usr-vsig2" stands for "usr-secondary-verity-sig". The shorthands work for every partition type with a verity suffix. The partition designators in image policies and image filters accept "-vty" and "-vsig" as well, so the same spelling works in repart.d/ files and in policies. Partition types are still displayed with their canonical long name. The label that repart derives when Label= is not set keeps the long spelling. Switching that default would change the labels of verity partitions in every new image built without Label=. A shorter label is available by setting Label= to the shorthand.
83 lines
4.1 KiB
XML
83 lines
4.1 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd.image-filter">
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<refentryinfo>
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<title>systemd.image-filter</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd.image-filter</refentrytitle>
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<manvolnum>7</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.image-filter</refname>
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<refpurpose>Disk Image Dissection Filter</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<para>In systemd, whenever a disk image (DDI) implementing the <ulink
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url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">UAPI.2 Discoverable
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Partitions Specification</ulink> is activated, a filter may be specified controlling which partitions to
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consider for mounting. Such a disk image dissection filter is a string that contains per-partition-type
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patterns, separated by colons (<literal>:</literal>). The individual rules consist of a partition
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identifier, an equal sign (<literal>=</literal>), and a shell globbing pattern applied to the GPT label
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string of the partition. See <citerefentry
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project='man-pages'><refentrytitle>glob</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
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details on shell globbing.</para>
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<para>The partition identifiers currently defined are: <option>root</option>, <option>usr</option>,
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<option>home</option>, <option>srv</option>, <option>esp</option>, <option>xbootldr</option>,
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<option>swap</option>, <option>root-verity</option>, <option>root-verity-sig</option>,
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<option>usr-verity</option>, <option>usr-verity-sig</option>, <option>tmp</option>,
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<option>var</option>. You can abbreviate the <literal>-verity</literal> and <literal>-verity-sig</literal>
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suffixes as <literal>-vty</literal> and <literal>-vsig</literal>, for example <option>usr-vsig</option>.
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These identifiers match the relevant partition types in the Discoverable
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Partitions Specification, but are agnostic to CPU architectures.</para>
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</refsect1>
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<refsect1>
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<title>Use</title>
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<para>Various systemd components that support operating with disk images support a
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<option>--image-filter=</option> command line option to specify the image filter to use. If no filter is
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specified all partitions in partition table are considered and no per-label filtering is applied (except
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that partitions with the <literal>_empty</literal> label are always ignored).</para>
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<para>For the host root file system image itself
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<citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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is responsible for processing the GPT partition table and making use of the included discoverable
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partitions. It accepts an image filter via the kernel command line option
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<option>systemd.image_filter=</option>.</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>The following image filter string dictates that for the root file system partition only partitions
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shall be considered whose label begins with <literal>ParticleOS-</literal>. For the
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<filename>/usr/</filename> partition the precise label <literal>ParticleOS_47110815</literal> is
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required.</para>
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<programlisting>root=ParticleOS-*:usr=ParticleOS_47110815</programlisting>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-dissect</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd.image-policy</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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