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This allows copying in arbitrary file systems on the block level into newly created partitions. Usecase: simple replicating OS installers or OS image builders.
458 lines
22 KiB
XML
458 lines
22 KiB
XML
<?xml version='1.0'?>
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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/4.2/docbookx.dtd">
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<refentry id="repart.d" conditional='ENABLE_REPART'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>repart.d</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>repart.d</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>repart.d</refname>
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<refpurpose>Partition Definition Files for Automatic Boot-Time Repartitioning</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><literallayout><filename>/etc/repart.d/*.conf</filename>
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<filename>/run/repart.d/*.conf</filename>
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<filename>/usr/lib/repart.d/*.conf</filename>
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</literallayout></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>repart.d/*.conf</filename> files describe basic properties of partitions of block
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devices of the local system. They may be used to declare types, names and sizes of partitions that shall
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exist. The
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<citerefentry><refentrytitle>systemd-repart</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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service reads these files and attempts to add new partitions currently missing and enlarge existing
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partitions according to these definitions. Operation is generally incremental, i.e. when applied, what
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exists already is left intact, and partitions are never shrunk, moved or deleted.</para>
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<para>These definition files are useful for implementing operating system images that are prepared and
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delivered with minimally sized images (for example lacking any state or swap partitions), and which on
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first boot automatically take possession of any remaining disk space following a few basic rules.</para>
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<para>Currently, support for partition definition files is only implemented for GPT partitition
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tables.</para>
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<para>Partition files are generally matched against any partitions already existing on disk in a simple
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algorithm: the partition files are sorted by their filename (ignoring the directory prefix), and then
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compared in order against existing partitions matching the same partition type UUID. Specifically, the
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first existing partition with a specific partition type UUID is assigned the first definition file with
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the same partition type UUID, and the second existing partition with a specific type UUID the second
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partition file with the same type UUID, and so on. Any left-over partition files that have no matching
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existing partition are assumed to define new partition that shall be created. Such partitions are
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appended to the end of the partition table, in the order defined by their names utilizing the first
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partition slot greater than the highest slot number currently in use. Any existing partitions that have
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no matching partition file are left as they are.</para>
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<para>Note that these partition definition files do not describe the contents of the partitions, such as
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the file system used. Separate mechanisms, such as
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<citerefentry><refentrytitle>systemd-growfs</refentrytitle><manvolnum>8</manvolnum></citerefentry> and
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<command>systemd-makefs</command> maybe be used to initialize or grow the file systems inside of these
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partitions.</para>
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</refsect1>
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<refsect1>
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<title>[Partition] Section Options</title>
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<variablelist>
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<varlistentry>
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<term><varname>Type=</varname></term>
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<listitem><para>The GPT partition type UUID to match. This may be a GPT partition type UUID such as
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<constant>4f68bce3-e8cd-4db1-96e7-fbcaf984b709</constant>, or one of the following special
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identifiers:</para>
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<table>
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<title>GPT partition type identifiers</title>
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<tgroup cols='2' align='left' colsep='1' rowsep='1'>
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<colspec colname="name" />
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<colspec colname="explanation" />
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<thead>
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<row>
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<entry>Identifier</entry>
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<entry>Explanation</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><constant>esp</constant></entry>
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<entry>EFI System Partition</entry>
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</row>
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<row>
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<entry><constant>xbootldr</constant></entry>
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<entry>Extended Boot Loader Partition</entry>
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</row>
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<row>
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<entry><constant>swap</constant></entry>
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<entry>Swap partition</entry>
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</row>
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<row>
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<entry><constant>home</constant></entry>
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<entry>Home (<filename>/home/</filename>) partition</entry>
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</row>
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<row>
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<entry><constant>srv</constant></entry>
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<entry>Server data (<filename>/srv/</filename>) partition</entry>
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</row>
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<row>
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<entry><constant>var</constant></entry>
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<entry>Variable data (<filename>/var/</filename>) partition</entry>
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</row>
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<row>
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<entry><constant>tmp</constant></entry>
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<entry>Temporary data (<filename>/var/tmp/</filename>) partition</entry>
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</row>
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<row>
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<entry><constant>linux-generic</constant></entry>
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<entry>Generic Linux file system partition</entry>
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</row>
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<row>
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<entry><constant>root</constant></entry>
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<entry>Root file system partition type appropriate for the local architecture (an alias for an architecture root file system partition type listed below, e.g. <constant>root-x86-64</constant>)</entry>
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</row>
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<row>
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<entry><constant>root-verity</constant></entry>
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<entry>Verity data for the root file system partition for the local architecture</entry>
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</row>
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<row>
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<entry><constant>root-secondary</constant></entry>
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<entry>Root file system partition of the secondary architecture of the local architecture; usually the matching 32bit architecture for the local 64bit architecture)</entry>
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</row>
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<row>
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<entry><constant>root-secondary-verity</constant></entry>
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<entry>Verity data for the root file system partition of the secondary architecture</entry>
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</row>
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<row>
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<entry><constant>root-x86</constant></entry>
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<entry>Root file system partition for the x86 (32bit, aka i386) architecture</entry>
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</row>
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<row>
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<entry><constant>root-x86-verity</constant></entry>
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<entry>Verity data for the x86 (32bit) root file system partition</entry>
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</row>
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<row>
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<entry><constant>root-x86-64</constant></entry>
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<entry>Root file system partition for the x86_64 (64bit, aka amd64) architecture</entry>
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</row>
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<row>
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<entry><constant>root-x86-64-verity</constant></entry>
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<entry>Verity data for the x86_64 (64bit) root file system partition</entry>
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</row>
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<row>
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<entry><constant>root-arm</constant></entry>
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<entry>Root file system partition for the ARM (32bit) architecture</entry>
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</row>
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<row>
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<entry><constant>root-arm-verity</constant></entry>
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<entry>Verity data for the ARM (32bit) root file system partition</entry>
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</row>
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<row>
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<entry><constant>root-arm64</constant></entry>
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<entry>Root file system partition for the ARM (64bit, aka aarch64) architecture</entry>
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</row>
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<row>
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<entry><constant>root-arm64-verity</constant></entry>
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<entry>Verity data for the ARM (64bit, aka aarch64) root file system partition</entry>
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</row>
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<row>
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<entry><constant>root-ia64</constant></entry>
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<entry>Root file system partition for the ia64 architecture</entry>
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</row>
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<row>
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<entry><constant>root-ia64-verity</constant></entry>
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<entry>Verity data for the ia64 root file system partition</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>This setting defaults to <constant>linux-generic</constant>.</para>
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<para>Most of the partition type UUIDs listed above are defined in the <ulink
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url="https://systemd.io/DISCOVERABLE_PARTITIONS">Discoverable Partitions
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Specification</ulink>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Label=</varname></term>
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<listitem><para>The textual label to assign to the partition if none is assigned yet. Note that this
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setting is not used for matching. It is also not used when a label is already set for an existing
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partition. It is thus only used when a partition is newly created or when an existing one had a no
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label set (that is: an empty label). If not specified a label derived from the partition type is
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automatically used. Simple specifier expansion is supported, see below.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>UUID=</varname></term>
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<listitem><para>The UUID to assign to the partition if none is assigned yet. Note that this
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setting is not used for matching. It is also not used when a UUID is already set for an existing
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partition. It is thus only used when a partition is newly created or when an existing one had a
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all-zero UUID set. If not specified a UUID derived from the partition type is automatically
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used.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Priority=</varname></term>
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<listitem><para>A numeric priority to assign to this partition, in the range -2147483648…2147483647,
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with smaller values indicating higher priority, and higher values indicating smaller priority. This
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priority is used in case the configured size constraints on the defined partitions do not permit
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fitting all partitions onto the available disk space. If the partitions do not fit, the highest
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numeric partition priority of all defined partitions is determined, and all defined partitions with
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this priority are removed from the list of new partitions to create (which may be multiple, if the
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same priority is used for multiple partitions). The fitting algorithm is then tried again. If the
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partitions still do not fit, the now highest numeric partition priority is determined, and the
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matching partitions removed too, and so on. Partitions of a priority of 0 or lower are never
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removed. If all partitions with a priority above 0 are removed and the partitions still do not fit on
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the device the operation fails. Note that this priority has no effect on ordering partitions, for
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that use the alphabetical order of the filenames of the partition definition files. Defaults to
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0.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Weight=</varname></term>
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<listitem><para>A numeric weight to assign to this partition in the range 0…1000000. Available disk
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space is assigned the defined partitions according to their relative weights (subject to the size
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constraints configured with <varname>SizeMinBytes=</varname>, <varname>SizeMaxBytes=</varname>), so
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that a partition with weight 2000 gets double the space as one with weight 1000, and a partition with
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weight 333 a third of that. Defaults to 1000.</para>
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<para>The <varname>Weight=</varname> setting is used to distribute available disk space in an
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"elastic" fashion, based on the disk size and existing partitions. If a partition shall have a fixed
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size use both <varname>SizeMinBytes=</varname> and <varname>SizeMaxBytes=</varname> with the same
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value in order to fixate the size to one value, in which case the weight has no
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effect.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>PaddingWeight=</varname></term>
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<listitem><para>Similar to <varname>Weight=</varname> but sets a weight for the free space after the
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partition (the "padding"). When distributing available space the weights of all partitions and all
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defined padding is summed, and then each partition and padding gets the fraction defined by its
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weight. Defaults to 0, i.e. by default no padding is applied.</para>
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<para>Padding is useful if empty space shall be left for later additions or a safety margin at the
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end of the device or between partitions.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SizeMinBytes=</varname></term>
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<term><varname>SizeMaxBytes=</varname></term>
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<listitem><para>Specifies minimum and maximum size constraints in bytes. Takes the usual K, M, G, T,
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… suffixes (to the base of 1024). If <varname>SizeMinBytes=</varname> is specified the partition is
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created at or grown to at least the specified size. If <varname>SizeMaxBytes=</varname> is specified
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the partition is created at or grown to at most the specified size. The precise size is determined
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through the weight value value configured with <varname>Weight=</varname>, see above. When
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<varname>SizeMinBytes=</varname> is set equal to <varname>SizeMaxBytes=</varname> the configured
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weight has no effect as the partition is explicitly sized to the specified fixed value. Note that
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partitions are never created smaller than 4096 bytes, and since partitions are never shrunk the
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previous size of the partition (in case the partition already exists) is also enforced as lower bound
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for the new size. The values should be specified as multiples of 4096 bytes, and are rounded upwards
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(in case of <varname>SizeMinBytes=</varname>) or downwards (in case of
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<varname>SizeMaxBytes=</varname>) otherwise. If the backing device does not provide enough space to
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fulfill the constraints placing the partition will fail. For partitions that shall be created,
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depending on the setting of <varname>Priority=</varname> (see above) the partition might be dropped
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and the placing algorithm restarted. By default a minimum size constraint of 10M and no maximum size
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constraint is set.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>PaddingMinBytes=</varname></term>
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<term><varname>PaddingMaxBytes=</varname></term>
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<listitem><para>Specifies minimum and maximum size constraints in bytes for the free space after the
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partition (the "padding"). Semantics are similar to <varname>SizeMinBytes=</varname> and
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<varname>SizeMaxBytes=</varname>, except that unlike partition sizes free space can be shrunk and can
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be as small as zero. By default no size constraints on padding are set, so that only
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<varname>PaddingWeight=</varname> determines the size of the padding applied.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>CopyBlocks=</varname></term>
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<listitem><para>Takes a path to a regular file, block device node or directory. If specified and the
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partition is newly created the data from the specified path is written to the newly created
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partition, on the block level. If a directory is specified the backing block device of the file
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system the directory is on is determined and the data read directly from that. This option is useful
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to efficiently replicate existing file systems on the block level on a new partition, for example to
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build a simple OS installer or OS image builder.</para>
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<para>The file specified here must have a size that is a multiple of the basic block size 512 and not
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be empty. If this option is used, the size allocation algorithm is slightly altered: the partition is
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created as least as big as required to fit the data in, i.e. the data size is an additional minimum
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size value taken into consideration for the allocation algorithm, similar to and in addition to the
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<varname>SizeMin=</varname> value configured above.</para>
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<para>This option has no effect if the partition it is declared for already exists, i.e. existing
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data is never overwritten. Note that the data is copied in before the partition table is updated,
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i.e. before the partition actually is persistently created. This provides robustness: it is
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guaranteed that the partition either doesn't exist or exists fully populated; it is not possible that
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the partition exists but is not or only partially populated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>FactoryReset=</varname></term>
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<listitem><para>Takes a boolean argument. If specified the partition is marked for removal during a
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factory reset operation. This functionality is useful to implement schemes where images can be reset
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into their original state by removing partitions and creating them anew. Defaults to off.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Specifiers</title>
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<para>Specifiers may be used in the <varname>Label=</varname> setting. The following expansions are understood:</para>
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<table class='specifiers'>
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<title>Specifiers available</title>
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<tgroup cols='3' align='left' colsep='1' rowsep='1'>
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<colspec colname="spec" />
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<colspec colname="mean" />
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<colspec colname="detail" />
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<thead>
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<row>
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<entry>Specifier</entry>
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<entry>Meaning</entry>
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<entry>Details</entry>
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</row>
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</thead>
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<tbody>
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<xi:include href="standard-specifiers.xml" xpointer="a"/>
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<xi:include href="standard-specifiers.xml" xpointer="b"/>
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<xi:include href="standard-specifiers.xml" xpointer="B"/>
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<xi:include href="standard-specifiers.xml" xpointer="H"/>
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<xi:include href="standard-specifiers.xml" xpointer="l"/>
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<xi:include href="standard-specifiers.xml" xpointer="m"/>
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<xi:include href="standard-specifiers.xml" xpointer="o"/>
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<xi:include href="standard-specifiers.xml" xpointer="v"/>
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<xi:include href="standard-specifiers.xml" xpointer="w"/>
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<xi:include href="standard-specifiers.xml" xpointer="W"/>
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<xi:include href="standard-specifiers.xml" xpointer="percent"/>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<example>
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<title>Grow the root partition to the full disk size at first boot</title>
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<para>With the following file the root partition is automatically grown to the full disk if possible during boot.</para>
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<para><programlisting># /usr/lib/repart.d/50-root.conf
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[Partition]
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Type=root
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</programlisting></para>
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</example>
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<example>
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<title>Create a swap and home partition automatically on boot, if missing</title>
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<para>The home partition gets all available disk space while the swap partition gets 1G at most and 64M
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at least. We set a priority > 0 on the swap partition to ensure the swap partition is not used if not
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enough space is available. For every three bytes assigned to the home partition the swap partition gets
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assigned one.</para>
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<para><programlisting># /usr/lib/repart.d/60-home.conf
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[Partition]
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Type=home
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</programlisting></para>
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<para><programlisting># /usr/lib/repart.d/70-swap.conf
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[Partition]
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Type=swap
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SizeMinBytes=64M
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SizeMaxBytes=1G
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Priority=1
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Weight=333
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</programlisting></para>
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</example>
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<example>
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<title>Create B partitions in an A/B Verity setup, if missing</title>
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<para>Let's say the vendor intends to update OS images in an A/B setup, i.e. with two root partitions
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(and two matching Verity partitions) that shall be used alternatingly during upgrades. To minimize
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image sizes the original image is shipped only with one root and one Verity partition (the "A" set),
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and the second root and Verity partitions (the "B" set) shall be created on first boot on the free
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space on the medium.</para>
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<para><programlisting># /usr/lib/repart.d/50-root.conf
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[Partition]
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Type=root
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SizeMinBytes=512M
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SizeMaxBytes=512M
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</programlisting></para>
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<para><programlisting># /usr/lib/repart.d/60-root-verity.conf
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[Partition]
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Type=root-verity
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SizeMinBytes=64M
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SizeMaxBytes=64M
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</programlisting></para>
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<para>The definitions above cover the "A" set of root partition (of a fixed 512M size) and Verity
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partition for the root partition (of a fixed 64M size). Let's use symlinks to create the "B" set of
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partitions, since after all they shall have the same properties and sizes as the "A" set.</para>
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<para><programlisting># ln -s 50-root.conf /usr/lib/repart.d/70-root-b.conf
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# ln -s 60-root-verity.conf /usr/lib/repart.d/80-root-verity-b.conf
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</programlisting></para>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-repart</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>sfdisk</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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