mirror of
https://github.com/systemd/systemd.git
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b00651cf43
Previously volatile-root was only checked if "/" wasn't backed by a block device, but the block device isn't necessarily original root block device (ex: if the rootfs is copied to a ext4 fs backed by zram in the initramfs), so we always want volatile-root checked. So shuffle the code around so volatile-root is checked first and fallback to the automatic logic. Fix #20557
316 lines
17 KiB
XML
316 lines
17 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/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-gpt-auto-generator" conditional='HAVE_BLKID'>
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<refentryinfo>
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<title>systemd-gpt-auto-generator</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-gpt-auto-generator</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-gpt-auto-generator</refname>
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<refpurpose>Generator for automatically discovering and mounting root, <filename>/home/</filename>,
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<filename>/srv/</filename>, <filename>/var/</filename> and <filename>/var/tmp/</filename> partitions, as
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well as discovering and enabling swap partitions, based on GPT partition type GUIDs</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>/usr/lib/systemd/system-generators/systemd-gpt-auto-generator</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-gpt-auto-generator</filename> is a unit generator that automatically discovers
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root, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>,
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<filename>/var/tmp/</filename>, the EFI System Partition, the Extended Boot Loader Partition and swap
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partitions and creates mount and swap units for them, based on the partition type GUIDs of GUID partition
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tables (GPT), see <ulink url="https://uefi.org/specifications">UEFI Specification</ulink>, chapter 5. It
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implements the <ulink url="https://systemd.io/DISCOVERABLE_PARTITIONS">Discoverable Partitions
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Specification</ulink>. Note that this generator has no effect on non-GPT systems, and on specific mount
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points that are directories already containing files. Also, on systems where the units are explicitly
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configured (for example, listed in <citerefentry
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project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>), the
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units this generator creates are overridden, but additional implicit dependencies might be
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created.</para>
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<para>This generator will only look for the root partition on the same physical disk the EFI System
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Partition (ESP) is located on. Note that support from the boot loader is required: the EFI variable
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<varname>LoaderDevicePartUUID</varname> of the <constant>4a67b082-0a4c-41cf-b6c7-440b29bb8c4f</constant>
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vendor UUID is used to determine from which partition, and hence the disk from which the system was
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booted. If the boot loader does not set this variable, this generator will not be able to autodetect the
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root partition. See the <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader
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Interface</ulink> for details.</para>
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<para>Similarly, this generator will only look for the other partitions on the same physical disk as the
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root partition. In this case, boot loader support is not required. These partitions will not be searched
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for on systems where the root file system is distributed on multiple disks, for example via btrfs RAID.
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</para>
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<para><filename>systemd-gpt-auto-generator</filename> is useful for centralizing file system
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configuration in the partition table and making configuration in <filename>/etc/fstab</filename> or on
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the kernel command line unnecessary.</para>
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<para>This generator looks for the partitions based on their
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partition type GUID. The following partition type GUIDs are
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identified:</para>
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<table>
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<title>Partition Type GUIDs</title>
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<tgroup cols='3' align='left' colsep='1' rowsep='1'>
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<colspec colname="guid" />
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<colspec colname="name" />
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<colspec colname="where" />
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<colspec colname="explanation" />
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<thead>
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<row>
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<entry>Partition Type GUID</entry>
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<entry>Name</entry>
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<entry>Mount Point</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>44479540-f297-41b2-9af7-d131d5f0458a</entry>
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<entry><filename>Root Partition (x86)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>On 32-bit 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>
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</row>
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<row>
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<entry>4f68bce3-e8cd-4db1-96e7-fbcaf984b709</entry>
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<entry><filename>Root Partition (x86-64)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>On 64-bit 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>
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</row>
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<row>
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<entry>69dad710-2ce4-4e3c-b16c-21a1d49abed3</entry>
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<entry><filename>Root Partition (32-bit ARM)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>On 32-bit ARM systems, the first ARM root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
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</row>
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<row>
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<entry>b921b045-1df0-41c3-af44-4c6f280d3fae</entry>
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<entry><filename>Root Partition (64-bit ARM)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>On 64-bit ARM systems, the first ARM root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
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</row>
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<row>
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<entry>993d8d3d-f80e-4225-855a-9daf8ed7ea97</entry>
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<entry><filename>Root Partition (Itanium/IA-64)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>On Itanium systems, the first Itanium root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
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</row>
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<row>
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<entry>77055800-792c-4f94-b39a-98c91b762bb6</entry>
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<entry><filename>Root Partition (LoongArch 64)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>On LoongArch 64-bit systems, the first LoongArch 64-bit root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
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</row>
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<row>
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<entry>60d5a7fe-8e7d-435c-b714-3dd8162144e1</entry>
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<entry><filename>Root Partition (RISCV-V 32)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>On RISC-V 32-bit systems, the first RISCV-V 32-bit root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
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</row>
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<row>
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<entry>72ec70a6-cf74-40e6-bd49-4bda08e8f224</entry>
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<entry><filename>Root Partition (RISCV-V 64)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>On RISC-V 64-bit systems, the first RISCV-V 64-bit root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
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</row>
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<row>
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<entry>933ac7e1-2eb4-4f13-b844-0e14e2aef915</entry>
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<entry>Home Partition</entry>
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<entry><filename>/home/</filename></entry>
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<entry>The first home partition on the disk the root partition is located on is mounted to <filename>/home/</filename>.</entry>
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</row>
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<row>
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<entry>3b8f8425-20e0-4f3b-907f-1a25a76f98e8</entry>
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<entry>Server Data Partition</entry>
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<entry><filename>/srv/</filename></entry>
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<entry>The first server data partition on the disk the root partition is located on is mounted to <filename>/srv/</filename>.</entry>
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</row>
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<row>
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<entry>4d21b016-b534-45c2-a9fb-5c16e091fd2d</entry>
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<entry>Variable Data Partition</entry>
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<entry><filename>/var/</filename></entry>
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<entry>The first variable data partition on the disk the root partition is located on is mounted to <filename>/var/</filename> — under the condition its partition UUID matches the first 128 bit of the HMAC-SHA256 of the GPT type uuid of this partition keyed by the machine ID of the installation stored in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</entry>
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</row>
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<row>
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<entry>7ec6f557-3bc5-4aca-b293-16ef5df639d1</entry>
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<entry>Temporary Data Partition</entry>
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<entry><filename>/var/tmp/</filename></entry>
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<entry>The first temporary data partition on the disk the root partition is located on is mounted to <filename>/var/tmp/</filename>.</entry>
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</row>
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<row>
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<entry>0657fd6d-a4ab-43c4-84e5-0933c84b4f4f</entry>
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<entry>Swap</entry>
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<entry>n/a</entry>
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<entry>All swap partitions located on the disk the root partition is located on are enabled.</entry>
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</row>
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<row>
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<entry>c12a7328-f81f-11d2-ba4b-00a0c93ec93b</entry>
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<entry>EFI System Partition (ESP)</entry>
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<entry><filename>/efi/</filename> or <filename>/boot/</filename></entry>
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<entry>The first ESP located on the disk the root partition is located on is mounted to <filename>/boot/</filename> or <filename>/efi/</filename>, see below.</entry>
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</row>
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<row>
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<entry>bc13c2ff-59e6-4262-a352-b275fd6f7172</entry>
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<entry>Extended Boot Loader Partition</entry>
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<entry><filename>/boot/</filename></entry>
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<entry>The first Extended Boot Loader Partition is mounted to <filename>/boot/</filename>, see below.</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 generator understands the following attribute flags for partitions:</para>
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<table>
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<title>Partition Attributes</title>
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<tgroup cols='4' align='left' colsep='1' rowsep='1'>
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<colspec colname="attribute" />
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<colspec colname="value" />
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<colspec colname="where" />
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<colspec colname="explanation" />
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<thead>
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<row>
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<entry>Name</entry>
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<entry>Value</entry>
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<entry>Applicable to</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>GPT_FLAG_READ_ONLY</constant></entry>
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<entry>0x1000000000000000</entry>
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<entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
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<entry>Partition is mounted read-only</entry>
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</row>
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<row>
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<entry><constant>GPT_FLAG_NO_AUTO</constant></entry>
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<entry>0x8000000000000000</entry>
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<entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
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<entry>Partition is not mounted automatically</entry>
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</row>
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<row>
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<entry><constant>GPT_FLAG_NO_BLOCK_IO_PROTOCOL</constant></entry>
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<entry>0x0000000000000002</entry>
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<entry>EFI System Partition (ESP)</entry>
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<entry>Partition is not mounted automatically</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>The <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename> and
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<filename>/var/tmp/</filename> partitions may be encrypted in LUKS format. In this case, a device mapper
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device is set up under the names <filename>/dev/mapper/home</filename>,
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<filename>/dev/mapper/srv</filename>, <filename>/dev/mapper/var</filename> and
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<filename>/dev/mapper/tmp</filename>. Note that this might create conflicts if the same partition is
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listed in <filename>/etc/crypttab</filename> with a different device mapper device name.</para>
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<para>When systemd is running in the initrd the <filename>/</filename> partition may be encrypted in LUKS
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format as well. In this case, a device mapper device is set up under the name <filename>/dev/mapper/root</filename>,
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and a <filename>sysroot.mount</filename> is set up that mounts the device under <filename>/sysroot</filename>.
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For more information, see <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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</para>
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<para>The root partition can be specified by symlinking <filename>/run/systemd/volatile-root</filename>
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to <filename>/dev/block/$major:$minor</filename>. This is especially useful if the root mount has been
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replaced by some form of volatile file system (overlayfs).
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</para>
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<para>Mount and automount units for the EFI System Partition (ESP) are generated on EFI systems. The ESP
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is mounted to <filename>/boot/</filename> (except if an Extended Boot Loader partition exists, see
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below), unless a mount point directory <filename>/efi/</filename> exists, in which case it is mounted
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there. Since this generator creates an automount unit, the mount will only be activated on-demand, when
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accessed. On systems where <filename>/boot/</filename> (or <filename>/efi/</filename> if it exists) is an
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explicitly configured mount (for example, listed in <citerefentry
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project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>) or where
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the <filename>/boot/</filename> (or <filename>/efi/</filename>) mount point is non-empty, no mount units
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are generated.</para>
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<para>If the disk contains an Extended Boot Loader partition, as defined in the <ulink
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url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, it is made
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available at <filename>/boot/</filename> (by means of an automount point, similar to the ESP, see
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above). If both an EFI System Partition and an Extended Boot Loader partition exist the latter is
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preferably mounted to <filename>/boot/</filename>. Make sure to create both <filename>/efi/</filename>
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and <filename>/boot/</filename> to ensure both partitions are mounted.</para>
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<para>When using this generator in conjunction with btrfs file
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systems, make sure to set the correct default subvolumes on them,
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using <command>btrfs subvolume set-default</command>.</para>
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<para><filename>systemd-gpt-auto-generator</filename> implements
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<citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
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</refsect1>
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<refsect1>
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<title>Kernel Command Line</title>
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<para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
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parameters:</para>
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<variablelist class='kernel-commandline-options'>
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<varlistentry>
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<term><varname>systemd.gpt_auto</varname></term>
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<term><varname>rd.systemd.gpt_auto</varname></term>
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<listitem><para>Those options take an optional boolean argument, and default to yes.
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The generator is enabled by default, and a negative value may be used to disable it.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>root=</varname></term>
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<listitem><para>When used with the special value <literal>gpt-auto</literal>, automatic discovery of
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the root partition based on the GPT partition type is enabled. Any other value disables this
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generator.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>rw</varname></term>
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<term><varname>ro</varname></term>
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<listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
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<para>Note that unlike most kernel command line options these settings do not override configuration
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in the file system, and the file system may be remounted later. See
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<citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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</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>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.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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