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diff --git a/man/bootup.xml b/man/bootup.xml new file mode 100644 index 0000000000..4cc4bafab7 --- /dev/null +++ b/man/bootup.xml @@ -0,0 +1,226 @@ +<?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"> + +<!-- + 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/>. +--> + +<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> + <refentrytitle>bootup</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>bootup</refname> + <refpurpose>System bootup process</refpurpose> + </refnamediv> + + <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 now (optionally) extracts and + executes an initial RAM disk image (initrd) such as + <citerefentry><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry> + which looks for the root file system. After the root + file system is found and mounted the initrd hands over + control to the 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>On shutdown the system manager stops all + services, unmounts all file systems (detaching the + storage technologies backing them), and then + (optionally) jumps back into the initrd code which + unmounts/detaches the root file system and the storage + it resides on. As last step the system is powered down.</para> + + <para>Additional information about the system boot + process may be found in + <citerefentry><refentrytitle>boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> + </refsect1> + + <refsect1> + <title>System Manager Bootup</title> + + <para>At boot, the system manager on the OS image is + responsible for initializing the required file + systems, services and drivers that are necessary for + operation of the system. On + <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> + systems this process is split up in various discrete + steps which are exposed as target units. (See + <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for detailed information about target units.) The + boot-up process is highly parallelized so that the + order in which specific target units are reached is not + deterministic, but still adheres to a limited amount + of ordering structure.</para> + + <para>When systemd starts up the system it will + activate all units that are dependencies of + <filename>default.target</filename> (as well as + recursively all dependencies of these + dependencies). Usually + <filename>default.target</filename> is simply an alias + of <filename>graphical.target</filename> or + <filename>multi-user.target</filename> depending on + whether the system is configured for a graphical UI or + only for a text console. To enforce minimal ordering + between the units pulled in a number of well-known + target units are available, as listed on + <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> + + <para>The following chart is a structural overview of + these well-known units and their position in the + boot-up logic. The arrows describe which units are + pulled in and ordered before which other units. Units + near the top are started before units nearer to the + bottom of the chart.</para> + +<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 + (various | rescue.service + sockets...) | | + | | v + v | <emphasis>rescue.target</emphasis> + sockets.target | + | | + \_________________ | + \| + 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> + + <para>Target units that are commonly used as boot + targets are <emphasis>emphasized</emphasis>. These + units are good choices as goal targets, for + example by passing them to the + <varname>systemd.unit=</varname> kernel command line + option (see + <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>) + or by symlinking <filename>default.target</filename> + to them.</para> + </refsect1> + + <refsect1> + <title>System Manager Shutdown</title> + + <para>System shutdown also consists of various target + units with some minimal ordering structure + applied:</para> + + + + +<programlisting> (conflicts with (conflicts with + all system all file system + services) mounts, swaps, + | cryptsetup + | devices, ...) + | | + v v + shutdown.target umount.target + | | + \_______ ______/ + \ / + v + (various low-level + services) + | + v + final.target + | + _____________________________________/ \_________________________________ + / | | \ + | | | | + v v v v +systemd-reboot.service systemd-poweroff.service systemd-halt.service systemd-kexec.service + | | | | + v v v v + <emphasis>reboot.target</emphasis> <emphasis>poweroff.target</emphasis> <emphasis>halt.target</emphasis> <emphasis>kexec.target</emphasis></programlisting> + + <para>Commonly used system shutdown targets are <emphasis>emphasized</emphasis>.</para> + </refsect1> + + <refsect1> + <title>See Also</title> + <para> + <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry> + </para> + </refsect1> + +</refentry> |