man/systemd-repart.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd-repart" conditional='ENABLE_REPART'
   7     xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>systemd-repart</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd-repart</refentrytitle>
  16     <manvolnum>8</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd-repart</refname>
  21     <refname>systemd-repart.service</refname>
  22     <refpurpose>Automatically grow and add partitions</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <cmdsynopsis>
  27       <command>systemd-repart</command>
  28       <arg choice="opt" rep="repeat">OPTIONS</arg>
  29       <arg choice="opt" rep="repeat"><replaceable><optional>BLOCKDEVICE</optional></replaceable></arg>
  30     </cmdsynopsis>
  31
  32     <para><filename>systemd-repart.service</filename></para>
  33   </refsynopsisdiv>
  34
  35   <refsect1>
  36     <title>Description</title>
  37
  38     <para><command>systemd-repart</command> grows and adds partitions to a partition table, based on the
  39     configuration files described in
  40     <citerefentry><refentrytitle>repart.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  41     </para>
  42
  43     <para>If invoked with no arguments, it operates on the block device backing the root file system partition
  44     of the OS, thus growing and adding partitions of the booted OS image itself. When called in the initial
  45     RAM disk it operates on the block device backing <filename>/sysroot/</filename> instead, i.e. on the
  46     block device the system will soon transition into. The <filename>systemd-repart.service</filename>
  47     service is generally run at boot in the initial RAM disk, in order to augment the partition table of the
  48     OS before its partitions are mounted. <command>systemd-repart</command> (mostly) operates in a purely
  49     incremental mode: it only grows existing and adds new partitions; it does not shrink, delete or move
  50     existing partitions. The service is intended to be run on every boot, but when it detects that the
  51     partition table already matches the installed <filename>repart.d/*.conf</filename> configuration
  52     files, it executes no operation.</para>
  53
  54     <para><command>systemd-repart</command> is intended to be used when deploying OS images, to automatically
  55     adjust them to the system they are running on, during first boot. This way the deployed image can be
  56     minimal in size and may be augmented automatically at boot when needed, taking possession of disk space
  57     available but not yet used. Specifically the following use cases are among those covered:</para>
  58
  59     <itemizedlist>
  60       <listitem><para>The root partition may be grown to cover the whole available disk space.</para></listitem>
  61       <listitem><para>A <filename>/home/</filename>, swap or <filename>/srv/</filename> partition can be
  62       added.</para></listitem>
  63       <listitem><para>A second (or third, …) root partition may be added, to cover A/B style setups
  64       where a second version of the root file system is alternatingly used for implementing update
  65       schemes. The deployed image would carry only a single partition ("A") but on first boot a second
  66       partition ("B") for this purpose is automatically created.</para></listitem>
  67     </itemizedlist>
  68
  69     <para>The algorithm executed by <command>systemd-repart</command> is roughly as follows:</para>
  70
  71     <orderedlist>
  72       <listitem><para>The <filename>repart.d/*.conf</filename> configuration files are loaded and parsed,
  73       and ordered by filename (without the directory prefix).</para></listitem>
  74
  75       <listitem><para>The partition table already existing on the block device is loaded and
  76       parsed.</para></listitem>
  77
  78       <listitem><para>The existing partitions in the partition table are matched up with the
  79       <filename>repart.d/*.conf</filename> files by GPT partition type UUID. The first existing partition
  80       of a specific type is assigned the first configuration file declaring the same type. The second
  81       existing partition of a specific type is then assigned the second configuration file declaring the same
  82       type, and so on. After this iterative assigning is complete any left-over existing partitions that have
  83       no matching configuration file are considered "foreign" and left as they are. And any configuration
  84       files for which no partition currently exists are understood as a request to create such a
  85       partition.</para></listitem>
  86
  87       <listitem><para>Taking the size constraints and weights declared in the configuration files into
  88       account, all partitions that shall be created are now allocated to the disk, taking up all free space,
  89       always respecting the size and padding requests. Similar, existing partitions that are determined to
  90       grow are grown. New partitions are always appended to the end of the existing partition table, taking
  91       the first partition table slot whose index is greater than the indexes of all existing
  92       partitions. Partition table slots are never reordered and thus partition numbers are ensured to remain
  93       stable. Note that this allocation happens in RAM only, the partition table on disk is not updated
  94       yet.</para></listitem>
  95
  96       <listitem><para>All existing partitions for which configuration files exist and which currently have no
  97       GPT partition label set will be assigned a label, either explicitly configured in the configuration or
  98       (if that's missing) derived automatically from the partition type. The same is done for all partitions
  99       that are newly created. These assignments are done in RAM only, too, the disk is not updated
 100       yet.</para></listitem>
 101
 102       <listitem><para>Similarly, all existing partitions for which configuration files exist and which
 103       currently have an all-zero identifying UUID will be assigned a new UUID. This UUID is cryptographically
 104       hashed from a common seed value together with the partition type UUID (and a counter in case multiple
 105       partitions of the same type are defined), see below. The same is done for all partitions that are
 106       created anew. These assignments are done in RAM only, too, the disk is not updated
 107       yet.</para></listitem>
 108
 109       <listitem><para>Similarly, if the disk's volume UUID is all zeroes it is also initialized, also
 110       cryptographically hashed from the same common seed value. Also, in RAM only, too.</para></listitem>
 111
 112       <listitem><para>The disk space assigned to new partitions (i.e. what was previously considered free
 113       space but is no longer) is now erased. Specifically, all file system signatures are removed, and if the
 114       device supports it the <constant>BLKDISCARD</constant> I/O control command is issued to inform the
 115       hardware that the space is empty now. In addition any "padding" between partitions and at the end of
 116       the device is similarly erased.</para></listitem>
 117
 118       <listitem><para>The new partition table is finally written to disk. The kernel is asked to reread the
 119       partition table.</para></listitem>
 120     </orderedlist>
 121
 122     <para>As exception to the normally strictly incremental operation, when called in a special "factory
 123     reset" mode, <command>systemd-repart</command> may also be used to erase existing partitions to
 124     reset an installation back to vendor defaults. This mode of operation is used when either the
 125     <option>--factory-reset=yes</option> switch is passed on the tool's command line, or the
 126     <option>systemd.factory_reset=yes</option> option specified on the kernel command line, or the
 127     <varname>FactoryReset</varname> EFI variable (vendor UUID
 128     <constant>8cf2644b-4b0b-428f-9387-6d876050dc67</constant>) is set to "yes". It alters the algorithm above
 129     slightly: between the 3rd and the 4th step above any partition marked explicitly via the
 130     <varname>FactoryReset=</varname> boolean is deleted, and the algorithm restarted, thus immediately
 131     re-creating these partitions anew empty.</para>
 132
 133     <para>Note that <command>systemd-repart</command> only changes partition tables, it does not create or
 134     resize any file systems within these partitions. A separate mechanism should be used for that, for
 135     example
 136     <citerefentry><refentrytitle>systemd-growfs</refentrytitle><manvolnum>8</manvolnum></citerefentry> and
 137     <command>systemd-makefs</command>.</para>
 138
 139     <para>The UUIDs identifying the new partitions created (or assigned to existing partitions that have no
 140     UUID yet), as well as the disk as a whole are hashed cryptographically from a common seed value. This
 141     seed value is usually the
 142     <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> of the
 143     system, so that the machine ID reproducibly determines the UUIDs assigned to all partitions. If the
 144     machine ID cannot be read (or the user passes <option>--seed=random</option>, see below) the seed is
 145     generated randomly instead, so that the partition UUIDs are also effectively random. The seed value may
 146     also be set explicitly, formatted as UUID via the <option>--seed=</option> option. By hashing these UUIDs
 147     from a common seed images prepared with this tool become reproducible and the result of the algorithm
 148     above deterministic.</para>
 149
 150     <para>The positional argument should specify the block device to operate on. Instead of a block device
 151     node path a regular file may be specified too, in which case the command operates on it like it would if
 152     a loopback block device node was specified with the file attached. If <option>--empty=create</option> is
 153     specified the specified path is created as regular file, which is useful for generating disk images from
 154     scratch.</para>
 155   </refsect1>
 156
 157   <refsect1>
 158     <title>Options</title>
 159
 160     <para>The following options are understood:</para>
 161
 162     <variablelist>
 163       <varlistentry>
 164         <term><option>--dry-run=</option></term>
 165         <listitem><para>Takes a boolean. If this switch is not specified <option>--dry-run=yes</option> is
 166         the implied default. Controls whether <filename>systemd-repart</filename> executes the requested
 167         re-partition operations or whether it should only show what it would do. Unless
 168         <option>--dry-run=no</option> is specified <filename>systemd-repart</filename> will not actually
 169         touch the device's partition table.</para></listitem>
 170       </varlistentry>
 171
 172       <varlistentry>
 173         <term><option>--empty=</option></term>
 174         <listitem><para>Takes one of <literal>refuse</literal>, <literal>allow</literal>,
 175         <literal>require</literal>, <literal>force</literal> or <literal>create</literal>. Controls how to
 176         operate on block devices that are entirely empty, i.e. carry no partition table/disk label yet. If
 177         this switch is not specified the implied default is <literal>refuse</literal>.</para>
 178
 179         <para>If <literal>refuse</literal> <command>systemd-repart</command> requires that the block device
 180         it shall operate on already carries a partition table and refuses operation if none is found. If
 181         <literal>allow</literal> the command will extend an existing partition table or create a new one if
 182         none exists. If <literal>require</literal> the command will create a new partition table if none
 183         exists so far, and refuse operation if one already exists. If <literal>force</literal> it will create
 184         a fresh partition table unconditionally, erasing the disk fully in effect. If
 185         <literal>force</literal> no existing partitions will be taken into account or survive the
 186         operation. Hence: use with care, this is a great way to lose all your data. If
 187         <literal>create</literal> a new loopback file is create under the path passed via the device node
 188         parameter, of the size indicated with <option>--size=</option>, see below.</para></listitem>
 189       </varlistentry>
 190
 191       <varlistentry>
 192         <term><option>--discard=</option></term>
 193
 194         <listitem><para>Takes a boolean. If this switch is not specified <option>--discard=yes</option> is
 195         the implied default. Controls whether to issue the <constant>BLKDISCARD</constant> I/O control
 196         command on the space taken up by any added partitions or on the space in between them. Usually, it's
 197         a good idea to issue this request since it tells the underlying hardware that the covered blocks
 198         shall be considered empty, improving performance. If operating on a regular file instead of a block
 199         device node, a sparse file is generated.</para></listitem>
 200       </varlistentry>
 201
 202       <varlistentry>
 203         <term><option>--size=</option></term>
 204
 205         <listitem><para>Takes a size in bytes, using the usual K, M, G, T suffixes. If used the specified
 206         device node path must refer to a regular file, which is then grown to the specified size if smaller,
 207         before any change is made to the partition table. This is not supported if the specified node is a
 208         block device. This switch has no effect if the file is already as large as the specified size or
 209         larger. The specified size is implicitly rounded up to multiples of 4096. When used with
 210         <option>--empty=create</option> this specifies the initial size of the loopback file to
 211         create.</para></listitem>
 212       </varlistentry>
 213
 214       <varlistentry>
 215         <term><option>--factory-reset=</option></term>
 216
 217         <listitem><para>Takes boolean. If this switch is not specified <option>--factory=reset=no</option> is
 218         the implied default. Controls whether to operate in "factory reset" mode, see above. If set to true
 219         this will remove all existing partitions marked with <varname>FactoryReset=</varname> set to yes
 220         early while executing the re-partitioning algorithm. Use with care, this is a great way to lose all
 221         your data. Note that partition files need to explicitly turn <varname>FactoryReset=</varname> on, as
 222         the option defaults to off. If no partitions are marked for factory reset this switch has no
 223         effect. Note that there are two other methods to request factory reset operation: via the kernel
 224         command line and via an EFI variable, see above.</para></listitem>
 225       </varlistentry>
 226
 227       <varlistentry>
 228         <term><option>--can-factory-reset</option></term>
 229
 230         <listitem><para>If this switch is specified the disk is not re-partitioned. Instead it is determined
 231         if any existing partitions are marked with <varname>FactoryReset=</varname>. If there are the tool
 232         will exit with exit status zero, otherwise non-zero. This switch may be used to quickly determine
 233         whether the running system supports a factory reset mechanism built on
 234         <command>systemd-repart</command>.</para></listitem>
 235       </varlistentry>
 236
 237       <varlistentry>
 238         <term><option>--root=</option></term>
 239
 240         <listitem><para>Takes a path to a directory to use as root file system when searching for
 241         <filename>repart.d/*.conf</filename> files and for the machine ID file to use as seed. By default
 242         when invoked on the regular system this defaults to the host's root file system
 243         <filename>/</filename>. If invoked from the initial RAM disk this defaults to
 244         <filename>/sysroot/</filename>, so that the tool operates on the configuration and machine ID stored
 245         in the root file system later transitioned into itself.</para></listitem>
 246       </varlistentry>
 247
 248       <varlistentry>
 249         <term><option>--seed=</option></term>
 250
 251         <listitem><para>Takes a UUID as argument or the special value <constant>random</constant>. If a UUID
 252         is specified the UUIDs to assign to partitions and the partition table itself are derived via
 253         cryptographic hashing from it. If not specified it is attempted to read the machine ID from the host
 254         (or more precisely, the root directory configured via <option>--root=</option>) and use it as seed
 255         instead, falling back to a randomized seed otherwise. Use <option>--seed=random</option> to force a
 256         randomized seed. Explicitly specifying the seed may be used to generated strictly reproducible
 257         partition tables.</para></listitem>
 258       </varlistentry>
 259
 260       <varlistentry>
 261         <term><option>--pretty=</option></term>
 262
 263         <listitem><para>Takes a boolean argument. If this switch is not specified, it defaults to on when
 264         called from an interactive terminal and off otherwise. Controls whether to show a user friendly table
 265         and graphic illustrating the changes applied.</para></listitem>
 266       </varlistentry>
 267
 268       <varlistentry>
 269         <term><option>--definitions=</option></term>
 270
 271         <listitem><para>Takes a file system path. If specified the <filename>*.conf</filename> files are read
 272         from the specified directory instead of searching in <filename>/usr/lib/repart.d/*.conf</filename>,
 273         <filename>/etc/repart.d/*.conf</filename>,
 274         <filename>/run/repart.d/*.conf</filename>.</para></listitem>
 275       </varlistentry>
 276
 277       <xi:include href="standard-options.xml" xpointer="help" />
 278       <xi:include href="standard-options.xml" xpointer="version" />
 279     </variablelist>
 280   </refsect1>
 281
 282   <refsect1>
 283     <title>See Also</title>
 284     <para>
 285       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 286       <citerefentry><refentrytitle>repart.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 287       <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 288     </para>
 289   </refsect1>
 290
 291 </refentry>