bootup.xml revision 013d8a39a6178179080bcfee9122b29cf9d29259
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3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek This file is part of systemd.
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek Copyright 2012 Lennart Poettering
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek systemd is free software; you can redistribute it and/or modify it
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek under the terms of the GNU Lesser General Public License as published by
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek the Free Software Foundation; either version 2.1 of the License, or
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek (at your option) any later version.
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek systemd is distributed in the hope that it will be useful, but
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek WITHOUT ANY WARRANTY; without even the implied warranty of
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek Lesser General Public License for more details.
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek You should have received a copy of the GNU Lesser General Public License
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek along with systemd; If not, see <http://www.gnu.org/licenses/>.
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <productname>systemd</productname>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <email>lennart@poettering.net</email>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <refentrytitle>bootup</refentrytitle>
301af7e4853ad0281402f8d86f5a77c6cb7ce9f4Josh Triplett <refpurpose>The System Bootup Process</refpurpose>
301af7e4853ad0281402f8d86f5a77c6cb7ce9f4Josh Triplett </refnamediv>
301af7e4853ad0281402f8d86f5a77c6cb7ce9f4Josh Triplett <para>A number of different components are involved in the
301af7e4853ad0281402f8d86f5a77c6cb7ce9f4Josh Triplett system boot. Immediately after power-up, the system
301af7e4853ad0281402f8d86f5a77c6cb7ce9f4Josh Triplett BIOS will do minimal hardware initialization, and hand
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek control over to a boot loader stored on a persistant
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek storage device. This boot loader will then invoke an
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek OS kernel from disk (or the network). In the Linux
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek case this kernel now (optionally) extracts and
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek executes an initial RAM disk image (initrd) such as
18ead1b00dff180a97507d014325cb46198e6657Chris Mayo <citerefentry><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>
18ead1b00dff180a97507d014325cb46198e6657Chris Mayo which looks for the root file system. After the root
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek file system is found and mounted the initrd hands over
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek control to the system manager (such as
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>)
e93549ef29c4123d9ee45acb5815048390201e49Zbigniew Jędrzejewski-Szmek stored on the OS image which is then responsible for
301af7e4853ad0281402f8d86f5a77c6cb7ce9f4Josh Triplett probing all remaining hardware, mounting all necessary
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek file systems and spawning all configured
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek services.</para>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <para>On shutdown the system manager stops all
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek services, unmounts all file systems (detaching the
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek storage technologies backing them), and then
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek (optionally) jumps back into the initrd code which
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek unmounts/detaches the root file system and the storage
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek it resides on. As last step the system powered down.</para>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <para>Additional information about the system boot
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek process may be found in
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <citerefentry><refentrytitle>boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <title>System Manager Bootup</title>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <para>At boot, the system manager on the OS image is
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek responsible for initializing the required file
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek systems, services and drivers that are necessary for
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek operation of the system. On
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek systems this process is split up in various discrete
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek steps which are exposed as target units. (See
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek for detailed information about target units.) The
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek boot-up process is highly parallelized so that the
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek order in which specific target units are reached is not
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek deterministic, but still adheres to a limited amount
8c9571d0ae50656f730a5e37378d5c3dcf3b9789Lennart Poettering of ordering structure.</para>
442f7f155358a7396a350d3c47ea42e86bee4024Chris Atkinson <para>When systemd starts up the system it will
8c9571d0ae50656f730a5e37378d5c3dcf3b9789Lennart Poettering activate all units that are dependencies of
8c9571d0ae50656f730a5e37378d5c3dcf3b9789Lennart Poettering <filename>default.target</filename> (as well as
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek recursively all dependencies of these
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek dependencies). Usually
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <filename>default.target</filename> is simply an alias
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek of <filename>graphical.target</filename> or
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <filename>multi-user.target</filename> depending on
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek whether the system is configured for a graphical UI or
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek only for a text console. To enforce minimal ordering
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek between the units pulled in a number of well-known
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek target units are available, as listed on
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek <para>The follow chart is a structural overview of
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek these well-known units and their position in the
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek boot-up logic. The arrows describe which units are
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek pulled in and ordered before which other units. Units
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek near the top are started before units nearer to the
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek bottom of the chart.</para>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek<programlisting>local-fs-pre.target
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering(various mounts and (various swap (various cryptsetup
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering fsck services...) devices...) devices...) (various low-level (various low-level
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering | | | services: udevd, API VFS mounts:
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering v v v tmpfiles, random mqueue, configfs,
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering local-fs.target swap.target cryptsetup.target seed, sysctl, ...) debugfs, ...)
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering \__________________|_________________ | ___________________|____________________/
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering _________________/|\___________________
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering sockets...) | |
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek v | <emphasis>rescue.target</emphasis>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek \_________________ |
0dc5d23c85db85f96b141d4d32deee8018e56a6aLennart Poettering _________________/| emergency.service
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek v v <emphasis>emergency.target</emphasis>
3cc765d2718ac9b4ff978044ceabf5ad59d73edfZbigniew Jędrzejewski-Szmek (various system (various system
<emphasis>reboot.target</emphasis> <emphasis>poweroff.target</emphasis> <emphasis>halt.target</emphasis> <emphasis>kexec.target</emphasis></programlisting>
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,