Systemd/man/systemd-gpt-auto-generator.xml
Lennart Poettering 73b80ec2d9 gpt-auto-generator: automatically find the root disk of the system
When run in an initrd and no root= argument is set (or is set to
root=gpt-auto) we will automatically look for the root partition on the
same disk the EFI ESP is located on.

Since we look for swap, /home and /srv on the disk the root partition is
located on, we hence have a fully discoverable chain:

    Firmware discovers the EFI ESP partition → the initrd discovers the
    root partition → the host OS discovers swap, /home, and /srv.

Note that this requires an EFI boot loader that sets the
LoaderDevicePartUUID EFI variable, such as Gummiboot.
2014-03-07 04:31:26 +01:00

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<?xml version="1.0"?>
<!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<refentry id="systemd-gpt-auto-generator">
<refentryinfo>
<title>systemd-gpt-auto-generator</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-gpt-auto-generator</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-gpt-auto-generator</refname>
<refpurpose>Generator for automatically discovering
and mounting root, <filename>/home</filename> and
<filename>/srv</filename> partitions, as well as
discovering and enabling swap partitions, based on GPT
partition type GUIDs.</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/usr/lib/systemd/system-generators/systemd-gpt-auto-generator</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-gpt-auto-generator</filename>
is a unit generator that automatically discovers root,
<filename>/home</filename>, <filename>/srv</filename>
and swap partitions and creates mount and swap units
for them, based on the the partition type GUIDs of
GUID partition tables (GPT). Note that this generator
has no effect on non-GPT systems, on systems where the
units are explicitly configured (for example, listed
in
<citerefentry><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>),
or where the mount points are non-empty.</para>
<para>This generator will only look for root
partitions on the same physical disk the EFI System
Partition (ESP) is located on. It will only look for
the other partitions on the same physical disk the
root file system is located on. These partitions will
not be search on systems where the root file system is
distributed on multiple disks, for example via btrfs
RAID.</para>
<para><filename>systemd-gpt-auto-generator</filename>
is useful for centralizing file system configuration
in the partition table and making manual configuration
in <filename>/etc/fstab</filename> or suchlike
unnecessary.</para>
<para>This generator looks for the partitions based on
their partition type GUID. The following partition
type GUIDs are identified:</para>
<table>
<title>Partition Type GUIDs</title>
<tgroup cols='3' align='left' colsep='1' rowsep='1'>
<colspec colname="guid" />
<colspec colname="name" />
<colspec colname="explanation" />
<thead>
<row>
<entry>Partition Type GUID</entry>
<entry>Name</entry>
<entry>Explanation</entry>
</row>
</thead>
<tbody>
<row>
<entry>44479540-f297-41b2-9af7d131d5f0458a</entry>
<entry><filename>Root Partition (x86)</filename></entry>
<entry>On 32bit x86 systems the first x86 root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
</row>
<row>
<entry>4f68bce3-e8cd-4db1-96e7fbcaf984b709</entry>
<entry><filename>Root Partition (x86-64)</filename></entry>
<entry>On 64bit x86 systems the first x86-64 root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
</row>
<row>
<entry>933ac7e1-2eb4-4f13-b8440e14e2aef915</entry>
<entry>Home Partition</entry>
<entry>The first home partition on the disk the root partition is located on is mounted to <filename>/home</filename>.</entry>
</row>
<row>
<entry>3b8f8425-20e0-4f3b-907f1a25a76f98e8</entry>
<entry>Server Data Partition</entry>
<entry>The first server data partition on the disk the root partition is located on is mounted to <filename>/srv</filename>.</entry>
</row>
<row>
<entry>0657fd6d-a4ab-43c4-84e50933c84b4f4f</entry>
<entry>Swap</entry>
<entry>All swap partitions located on the disk the root partition is located on are enabled.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>The <filename>/home</filename> and
<filename>/srv</filename> partitions may be encrypted
in LUKS format. In this case a device mapper device is
set up under the names
<filename>/dev/mapper/home</filename> and
<filename>/dev/mapper/srv</filename>. Note that this
might create conflicts if the same partition is listed
in <filename>/etc/crypttab</filename> with a different
device mapper device name.</para>
<para>Also note that
<citerefentry><refentrytitle>systemd-efi-boot-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
will mount the EFI System Partition (ESP) to
<filename>/boot</filename> if not otherwise mounted.</para>
<para>When using this generator in conjunction with
btrfs file systems make sure to set the correct
default subvolumes on them, using <command>btrfs
subvolume set-default</command>.</para>
<para><filename>systemd-gpt-auto-generator</filename>
implements the <ulink
url="http://www.freedesktop.org/wiki/Software/systemd/Generators">generator
specification</ulink>.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-efi-boot-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>