<?xml version='1.0'?> <!--*-nxml-*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
-
-<!--
- SPDX-License-Identifier: LGPL-2.1+
-
- This file is part of systemd.
-
- Copyright 2012 Lennart Poettering
-
- systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 2.1 of the License, or
- (at your option) any later version.
-
- systemd is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with systemd; If not, see <http://www.gnu.org/licenses/>.
--->
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="bootup">
<refentryinfo>
<title>bootup</title>
<productname>systemd</productname>
-
- <authorgroup>
- <author>
- <contrib>Developer</contrib>
- <firstname>Lennart</firstname>
- <surname>Poettering</surname>
- <email>lennart@poettering.net</email>
- </author>
- </authorgroup>
</refentryinfo>
<refmeta>
<refsect1>
<title>Description</title>
- <para>A number of different components are involved in the system
- boot. Immediately after power-up, the system BIOS will do minimal
- hardware initialization, and hand control over to a boot loader
- stored on a persistent storage device. This boot loader will then
- invoke an OS kernel from disk (or the network). In the Linux case,
- this kernel (optionally) extracts and executes an initial RAM disk
- image (initrd), such as generated by
- <citerefentry project='die-net'><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
- which looks for the root file system (possibly using
- <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- for this). After the root file system is found and mounted, the
- initrd hands over control to the host's system manager (such as
- <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>)
- stored on the OS image, which is then responsible for probing all
- remaining hardware, mounting all necessary file systems and
- spawning all configured services.</para>
+ <para>A number of different components are involved in the boot of a Linux system. Immediately after
+ power-up, the system firmware will do minimal hardware initialization, and hand control over to a boot
+ loader (e.g.
+ <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> or
+ <ulink url="https://www.gnu.org/software/grub/">GRUB</ulink>) stored on a persistent storage device. This
+ boot loader will then invoke an OS kernel from disk (or the network). On systems using EFI or other types
+ of firmware, this firmware may also load the kernel directly.</para>
+
+ <para>The kernel (optionally) mounts an in-memory file system, often generated by
+ <citerefentry project='man-pages'><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ which looks for the root file system. Nowadays this is usually implemented as an initramfs — a compressed
+ archive which is extracted when the kernel boots up into a lightweight in-memory file system based on
+ tmpfs, but in the past normal file systems using an in-memory block device (ramdisk) were used, and the
+ name "initrd" is still used to describe both concepts. It's the boot loader or the firmware that loads
+ both the kernel and initrd/initramfs images into memory, but the kernel which interprets it as a file
+ system. <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> may
+ be used to manage services in the initrd, similarly to the real system.</para>
+
+ <para>After the root file system is found and mounted, the initrd hands over control to the host's system
+ manager (such as
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>) stored in
+ the root file system, which is then responsible for probing all remaining hardware, mounting all
+ necessary file systems and spawning all configured services.</para>
<para>On shutdown, the system manager stops all services, unmounts
all file systems (detaching the storage technologies backing
<!-- note: do not use unicode ellipsis here, because docbook will replace that
with three dots anyway, messing up alignment -->
-<programlisting>local-fs-pre.target
- |
- v
-(various mounts and (various swap (various cryptsetup
- fsck services...) devices...) devices...) (various low-level (various low-level
- | | | services: udevd, API VFS mounts:
- v v v tmpfiles, random mqueue, configfs,
- local-fs.target swap.target cryptsetup.target seed, sysctl, ...) debugfs, ...)
- | | | | |
- \__________________|_________________ | ___________________|____________________/
- \|/
- v
- sysinit.target
- |
- ____________________________________/|\________________________________________
- / | | | \
- | | | | |
- v v | v v
- (various (various | (various rescue.service
- timers...) paths...) | sockets...) |
- | | | | v
- v v | v <emphasis>rescue.target</emphasis>
- timers.target paths.target | sockets.target
- | | | |
- v \_________________ | ___________________/
- \|/
- v
- basic.target
- |
- ____________________________________/| emergency.service
- / | | |
- | | | v
- v v v <emphasis>emergency.target</emphasis>
- display- (various system (various system
- manager.service services services)
- | required for |
- | graphical UIs) v
- | | <emphasis>multi-user.target</emphasis>
- | | |
- \_________________ | _________________/
- \|/
- v
- <emphasis>graphical.target</emphasis></programlisting>
+<programlisting> cryptsetup-pre.target
+ |
+(various low-level v
+ API VFS mounts: (various cryptsetup devices...)
+ mqueue, configfs, | |
+ debugfs, ...) v |
+ | cryptsetup.target |
+ | (various swap | | remote-fs-pre.target
+ | devices...) | | | |
+ | | | | | v
+ | v local-fs-pre.target | | | (network file systems)
+ | swap.target | | v v |
+ | | v | remote-cryptsetup.target |
+ | | (various low-level (various mounts and | | |
+ | | services: udevd, fsck services...) | | remote-fs.target
+ | | tmpfiles, random | | | /
+ | | seed, sysctl, ...) v | | /
+ | | | local-fs.target | | /
+ | | | | | | /
+ \____|______|_______________ ______|___________/ | /
+ \ / | /
+ v | /
+ sysinit.target | /
+ | | /
+ ______________________/|\_____________________ | /
+ / | | | \ | /
+ | | | | | | /
+ v v | v | | /
+ (various (various | (various | |/
+ timers...) paths...) | sockets...) | |
+ | | | | | |
+ v v | v | |
+timers.target paths.target | sockets.target | |
+ | | | | v |
+ v \_______ | _____/ rescue.service |
+ \|/ | |
+ v v |
+ basic.target <emphasis>rescue.target</emphasis> |
+ | |
+ ________v____________________ |
+ / | \ |
+ | | | |
+ v v v |
+ display- (various system (various system |
+ manager.service services services) |
+ | required for | |
+ | graphical UIs) v v
+ | | <emphasis>multi-user.target</emphasis>
+emergency.service | | |
+ | \_____________ | _____________/
+ v \|/
+<emphasis>emergency.target</emphasis> v
+ <emphasis>graphical.target</emphasis></programlisting>
<para>Target units that are commonly used as boot targets are
<emphasis>emphasized</emphasis>. These units are good choices as
later in boot.</para>
</refsect1>
+ <refsect1>
+ <title>User manager startup</title>
+
+ <para>The system manager starts the <filename>user@<replaceable>uid</replaceable>.service</filename> unit
+ for each user, which launches a separate unprivileged instance of <command>systemd</command> for each
+ user — the user manager. Similarly to the system manager, the user manager starts units which are pulled
+ in by <filename>default.target</filename>. The following chart is a structural overview of the well-known
+ user units. For non-graphical sessions, <filename>default.target</filename> is used. Whenever the user
+ logs into a graphical session, the login manager will start the
+ <filename>graphical-session.target</filename> target that is used to pull in units required for the
+ graphical session. A number of targets (shown on the right side) are started when specific hardware is
+ available to the user.</para>
+
+<programlisting>
+ (various (various (various
+ timers...) paths...) sockets...) (sound devices)
+ | | | |
+ v v v v
+ timers.target paths.target sockets.target sound.target
+ | | |
+ \______________ _|_________________/ (bluetooth devices)
+ \ / |
+ V v
+ basic.target bluetooth.target
+ |
+ __________/ \_______ (smartcard devices)
+ / \ |
+ | | v
+ | v smartcard.target
+ v graphical-session-pre.target
+ (various user services) | (printers)
+ | v |
+ | (services for the graphical session) v
+ | | printer.target
+ v v
+ <emphasis>default.target</emphasis> graphical-session.target</programlisting>
+
+ </refsect1>
+
<refsect1>
<title>Bootup in the Initial RAM Disk (initrd)</title>
<para>The initial RAM disk implementation (initrd) can be set up
using systemd as well. In this case, boot up inside the initrd
follows the following structure.</para>
- <para>The default target in the initrd is
+ <para>systemd detects that it is run within an initrd by checking
+ for the file <filename>/etc/initrd-release</filename>.
+ The default target in the initrd is
<filename>initrd.target</filename>. The bootup process begins
identical to the system manager bootup (see above) until it
reaches <filename>basic.target</filename>. From there, systemd
so no filesystems can be mounted before the check is complete.
When the root device becomes available,
- <filename>initd-root-device.target</filename> is reached.
+ <filename>initrd-root-device.target</filename> is reached.
If the root device can be mounted at
<filename>/sysroot</filename>, the
<filename>sysroot.mount</filename> unit becomes active and
<para>Commonly used system shutdown targets are <emphasis>emphasized</emphasis>.</para>
<para>Note that
- <citerefentry>system<refentrytitle>systemd-halt.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-halt.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<filename>systemd-reboot.service</filename>, <filename>systemd-poweroff.service</filename> and
<filename>systemd-kexec.service</filename> will transition the system and server manager (PID 1) into the second
phase of system shutdown (implemented in the <filename>systemd-shutdown</filename> binary), which will unmount any
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-halt.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
- <citerefentry project='die-net'><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ <citerefentry project='man-pages'><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
projects / thirdparty / systemd.git / blobdiff