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