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man: introduce bootup(7)
2012-06-23 05:14:19 +08:00
<?xml version='1.0'?> <!--*-nxml-*-->
man: use same header for all files The "include" files had type "book" for some raeason. I don't think this is meaningful. Let's just use the same everywhere. $ perl -i -0pe 's^..DOCTYPE (book|refentry) PUBLIC "-//OASIS//DTD DocBook XML V4.[25]//EN"\s+"http^<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"\n "http^gms' man/*.xml
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
man: revert dynamic paths for split-usr setups This did not really work out as we had hoped. Trying to do this upstream introduced several problems that probably makes it better suited as a downstream patch after all. At any rate, it is not releaseable in the current state, so we at least need to revert this before the release. * by adjusting the path to binaries, but not do the same thing to the search path we end up with inconsistent man-pages. Adjusting the search path too would be quite messy, and it is not at all obvious that this is worth the effort, but at any rate it would have to be done before we could ship this. * this means that distributed man-pages does not make sense as they depend on config options, and for better or worse we are still distributing man pages, so that is something that definitely needs sorting out before we could ship with this patch. * we have long held that split-usr is only minimally supported in order to boot, and something we hope will eventually go away. So before we start adding even more magic/effort in order to make this work nicely, we should probably question if it makes sense at all.
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
man: standarize on one-line license header No need to waste space, and uniformity is good. $ perl -i -0pe 's|\n+<!--\s*SPDX-License-Identifier: LGPL-2.1..\s*-->|\n<!-- SPDX-License-Identifier: LGPL-2.1+ -->|gms' man/*.xml
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
man: introduce bootup(7)
2012-06-23 05:14:19 +08:00
<refentry id="bootup">
Reindent man pages to 2ch
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<refentryinfo>
<title>bootup</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>bootup</refentrytitle>
<manvolnum>7</manvolnum>
</refmeta>
<refnamediv>
<refname>bootup</refname>
<refpurpose>System bootup process</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
man: update description of initrd in bootup(7) Mention that initramfs is used, not initrd, even though we still call it that. Also add links and clarify who loads the initramfs.
2019-03-22 20:10:39 +08:00
<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
Reindent man pages to 2ch
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<citerefentry project='die-net'><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
man: update description of initrd in bootup(7) Mention that initramfs is used, not initrd, even though we still call it that. Also add links and clarify who loads the initramfs.
2019-03-22 20:10:39 +08:00
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>
Reindent man pages to 2ch
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<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 a last step, the system is powered down.</para>
<para>Additional information about the system boot process may be
found in
<citerefentry project='man-pages'><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>
man: introduce bootup(7)
2012-06-23 05:14:19 +08:00
man: use unicode ellipsis in one more place (#8496) Also add note where it should *not* be used. https://github.com/systemd/systemd/pull/8408#discussion_r175606771
2018-03-20 16:54:01 +08:00
<!-- note: do not use unicode ellipsis here, because docbook will replace that
with three dots anyway, messing up alignment -->
man: add remote-*.targets to the bootup sequence I think this makes it easier to see the difference between local and remote mounts. Make the graph a bit narrower while at it.
2019-12-18 17:32:03 +08:00
<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>
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<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>)
man: fix diagrams in bootup(7) Fallout from 798d3a524e.
2015-02-04 22:35:37 +08:00
or by symlinking <filename>default.target</filename> to them.
</para>
Reindent man pages to 2ch
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<para><filename>timers.target</filename> is pulled-in by
<filename>basic.target</filename> asynchronously. This allows
timers units to depend on services which become only available
later in boot.</para>
</refsect1>
man: add section about user manager units
2019-12-18 18:23:30 +08:00
<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
tree-wide: fix spelling errors Based on a report from Fossies.org using Codespell. Followup to #15436
2020-04-22 02:46:53 +08:00
graphical session. A number of targets (shown on the right side) are started when specific hardware is
man: add section about user manager units
2019-12-18 18:23:30 +08:00
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 sesion) v
| | printer.target
v v
<emphasis>default.target</emphasis> graphical-session.target</programlisting>
</refsect1>
Reindent man pages to 2ch
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<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>
Document /etc/initrd-release When systemd is started, it detects initrd by checking for that file The usage of that file is not documented anywhere, so mention it early in the most relevant man-page I could find.
2019-04-26 06:49:57 +08:00
<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
Reindent man pages to 2ch
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<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
approaches the special target <filename>initrd.target</filename>.
Document an edge-case with resume and mounting (#4581) When trying to read keyfiles from an encrypted partition to unlock the swap, a cyclic dependency is generated because systemd can not mount the filesystem before it has checked if there is a swap to resume from. Closes #3940
2016-11-23 12:19:56 +08:00
Before any file systems are mounted, it must be determined whether
the system will resume from hibernation or proceed with normal boot.
This is accomplished by <filename>systemd-hibernate-resume@.service</filename>
which must be finished before <filename>local-fs-pre.target</filename>,
so no filesystems can be mounted before the check is complete.
Create initrd-root-device.target synchronization point (#3239) Add a synchronization point so that custom initramfs units can run after the root device becomes available, before it is fsck'd and mounted. This is useful for custom initramfs units that may modify the root disk partition table, where the root device is not known in advance (it's dynamically selected by the generators).
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When the root device becomes available,
Fix typo on initrd-root-device.target
2020-03-06 20:51:28 +08:00
<filename>initrd-root-device.target</filename> is reached.
Reindent man pages to 2ch
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If the root device can be mounted at
<filename>/sysroot</filename>, the
<filename>sysroot.mount</filename> unit becomes active and
<filename>initrd-root-fs.target</filename> is reached. The service
<filename>initrd-parse-etc.service</filename> scans
<filename>/sysroot/etc/fstab</filename> for a possible
<filename>/usr</filename> mount point and additional entries
marked with the <emphasis>x-initrd.mount</emphasis> option. All
entries found are mounted below <filename>/sysroot</filename>, and
<filename>initrd-fs.target</filename> is reached. The service
<filename>initrd-cleanup.service</filename> isolates to the
<filename>initrd-switch-root.target</filename>, where cleanup
services can run. As the very last step, the
<filename>initrd-switch-root.service</filename> is activated,
which will cause the system to switch its root to
<filename>/sysroot</filename>.
</para>
man: fix diagrams in bootup(7) Fallout from 798d3a524e.
2015-02-04 22:35:37 +08:00
<programlisting> : (beginning identical to above)
:
v
basic.target
| emergency.service
______________________/| |
/ | v
Create initrd-root-device.target synchronization point (#3239) Add a synchronization point so that custom initramfs units can run after the root device becomes available, before it is fsck'd and mounted. This is useful for custom initramfs units that may modify the root disk partition table, where the root device is not known in advance (it's dynamically selected by the generators).
2016-05-13 00:42:39 +08:00
| initrd-root-device.target <emphasis>emergency.target</emphasis>
| |
| v
| sysroot.mount
man: fix diagrams in bootup(7) Fallout from 798d3a524e.
2015-02-04 22:35:37 +08:00
| |
| v
| initrd-root-fs.target
| |
| v
v initrd-parse-etc.service
(custom initrd |
services...) v
| (sysroot-usr.mount and
| various mounts marked
| with fstab option
| x-initrd.mount...)
| |
| v
| initrd-fs.target
\______________________ |
\|
v
initrd.target
|
v
initrd-cleanup.service
isolates to
initrd-switch-root.target
|
v
______________________/|
/ v
| initrd-udevadm-cleanup-db.service
v |
(custom initrd |
services...) |
\______________________ |
\|
v
initrd-switch-root.target
|
v
initrd-switch-root.service
|
v
Transition to Host OS</programlisting>
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</refsect1>
<refsect1>
<title>System Manager Shutdown</title>
<para>System shutdown with systemd also consists of various target
units with some minimal ordering structure applied:</para>
man: fix diagrams in bootup(7) Fallout from 798d3a524e.
2015-02-04 22:35:37 +08:00
<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
units: rename halt/hibernate/kexec/poweroff/reboot/suspend to systed-xxx These service units also execute our own code, hence rename the accordingly and prefix them with systemd-
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systemd-reboot.service systemd-poweroff.service systemd-halt.service systemd-kexec.service
man: fix diagrams in bootup(7) Fallout from 798d3a524e.
2015-02-04 22:35:37 +08:00
| | | |
v v v v
<emphasis>reboot.target</emphasis> <emphasis>poweroff.target</emphasis> <emphasis>halt.target</emphasis> <emphasis>kexec.target</emphasis></programlisting>
Reindent man pages to 2ch
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man: document that there's a second phase of shutdown in bootup(7)
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<para>Commonly used system shutdown targets are <emphasis>emphasized</emphasis>.</para>
<para>Note that
man: remove spurious 'system'
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<citerefentry><refentrytitle>systemd-halt.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
man: document that there's a second phase of shutdown in bootup(7)
2018-03-22 03:57:06 +08:00
<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
remaining file systems, kill any remaining processes and release any other remaining resources, in a simple and
robust fashion, without taking any service or unit concept into account anymore. At that point, regular
applications and resources are generally terminated and released already, the second phase hence operates only as
safety net for everything that couldn't be stopped or released for some reason during the primary, unit-based
shutdown phase described above.</para>
Reindent man pages to 2ch
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</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry project='man-pages'><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>,
man: document that there's a second phase of shutdown in bootup(7)
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<citerefentry><refentrytitle>systemd-halt.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
Reindent man pages to 2ch
2015-02-04 10:14:13 +08:00
<citerefentry project='die-net'><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
man: introduce bootup(7)
2012-06-23 05:14:19 +08:00
</refentry>
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