chiark / gitweb /
mount/service: drop FsckPassNo support
[elogind.git] / man / bootup.xml
index ae84cff..65c2cee 100644 (file)
 
         <refnamediv>
                 <refname>bootup</refname>
-                <refpurpose>The System Bootup Process</refpurpose>
+                <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 persistant
-                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
+                <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><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
+                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
+                <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 powered down.</para>
+                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
@@ -88,7 +91,7 @@
                 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
+                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
                 deterministic, but still adheres to a limited amount
                 of ordering structure.</para>
 
-                <para>When systemd starts up the system it will
+                <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
+                dependencies). Usually,
                 <filename>default.target</filename> is simply an alias
                 of <filename>graphical.target</filename> or
-                <filename>multi-user.target</filename> depending on
+                <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
+                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 follow chart is a structural overview of
+                <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
                                                v
                                         sysinit.target
                                                |
-                             _________________/|\___________________
-                            /                  |                    \
-                            |                  |                    |
-                            v                  |                    v
-                        (various               |              rescue.service
-                       sockets...)             |                    |
-                            |                  |                    v
-                            v                  |              <emphasis>rescue.target</emphasis>
-                     sockets.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
                                          basic.target
                                                |
-                             _________________/|                                 emergency.service
-                            /                  |                                         |
-                            |                  |                                         v
-                            v                  v                                 <emphasis>emergency.target</emphasis>
-                     (various system    (various system
                       services           services)
-                      required for             |
-                     graphical UIs)            v
-                            |           <emphasis>multi-user.target</emphasis>
-                            |                  |
-                            | _________________/
-                            |/
+          ____________________________________/|                                 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>
+                  <emphasis>graphical.target</emphasis></programlisting>
 
                 <para>Target units that are commonly used as boot
                 targets are <emphasis>emphasized</emphasis>. These
         </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 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
-reboot.service    poweroff.service   halt.service   kexec.service
-       |                  |                |              |
-       v                  v                v              v
-<emphasis>reboot.target</emphasis>     <emphasis>poweroff.target</emphasis>    <emphasis>halt.target</emphasis>    <emphasis>kexec.target</emphasis></programlisting>
+                <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>
@@ -219,7 +310,8 @@ reboot.service    poweroff.service   halt.service   kexec.service
                         <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>
+                        <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>dracut</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                 </para>
         </refsect1>