- <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>
+ <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 (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>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>