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<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 (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>
+ <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>
<programlisting>local-fs-pre.target
- |
- v
+ |
+ 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,
+ 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>
-
- <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>
-
- <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>
-
- <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
- <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>. 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>
-
-<programlisting> : (beginning identical to above)
- :
- v
- basic.target
- | emergency.service
- ______________________/| |
- / | v
- | sysroot.mount <emphasis>emergency.target</emphasis>
- | |
- | 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>
- </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>
-
-
-
-
-<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
+ | | | | |
+ \__________________|_________________ | ___________________|____________________/
+ \|/
+ 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>
+
+ <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>
+
+ <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>
+
+ <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
+ <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>.
+ 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>
+
+<programlisting> : (beginning identical to above)
+ :
+ v
+ basic.target
+ | emergency.service
+ ______________________/| |
+ / | v
+ | sysroot.mount <emphasis>emergency.target</emphasis>
+ | |
+ | 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>
+ </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>
+
+<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 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>,
- <citerefentry project='die-net'><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>
- </para>
- </refsect1>
+ | | | |
+ 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 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>,
+ <citerefentry project='die-net'><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ </para>
+ </refsect1>
</refentry>
~ianmdlvl / elogind.git / blobdiff