Make initrd.target the default target in the initrd

First, rename root-fs.target to initrd-root-fs.target to clarify its usage.

Mount units with "x-initrd-rootfs.mount" are now ordered before
initrd-root-fs.target. As we sometimes construct /sysroot mounts in
/etc/fstab in the initrd, we want these to be mounted before the
initrd-root-fs.target is active.

initrd.target can be the default target in the initrd.

                             (normal startup)
                                    :
                                    :
                                    v
                              basic.target
                                    |
             ______________________/|
            /                       |
            |                  sysroot.mount
            |                       |
            |                       v
            |             initrd-root-fs.target
            |                       |
            |                       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
             ______________________/|
            /                       |
            |        initrd-udevadm-cleanup-db.service
            |                       |
(custom initrd services)            |
            |                       |
            \______________________ |
                                   \|
                                    v
                        initrd-switch-root.target
                                    |
                                    v
                        initrd-switch-root.service
                                    |
                                    v
                               switch-root

1 files changed, 73 insertions, 0 deletions

diff --git a/man/bootup.xml b/man/bootup.xml
index f65abf5452..6bd22ef476 100644
--- a/man/bootup.xml
+++ b/man/bootup.xml
@@ -174,6 +174,79 @@
         </refsect1>
 
         <refsect1>
+                <title>Systemd in the Initrd</title>
+                <para>If the initrd creation tool used the services provided
+                by systemd, the default target in the initrd is the
+                initrd-fs.target. The process is the same as above until the basic.target is reached.
+                Systemd now continues to the initrd.target. If the root device could be mounted
+                on /sysroot, the sysroot.mount unit is active and the initrd-root-fs.target is reached.
+                initrd-parse-etc.service scans /sysroot/etc/fstab for the /usr mountpoint and for entries
+                marked with the <emphasis>x-initrd.mount</emphasis> option set. If these mountpoint are
+                mounted in /sysroot, the initrd-fs.target is reached.
+                The initrd-cleanup.service isolates to the initrd-switch-root.target,
+                where cleanup services can run. At the very last end
+                initrd-switch-root.service is activated, which will cause
+                the system to switch root to /sysroot.
+                </para>
+
+<programlisting>
+                                        (same as above)
+                                               :
+                                               :
+                                               v
+                                         basic.target
+                                               |                                 emergency.service
+                        ______________________/|                                         |
+                       /                       |                                         v
+                       |                  sysroot.mount                          <emphasis>emergency.target</emphasis>
+                       |                       |
+                       |                       v
+                       |             initrd-root-fs.target
+                       |                       |
+                       |                       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
+                        ______________________/|
+                       /                       |
+                       |        initrd-udevadm-cleanup-db.service
+                       |                       |
+           (custom initrd services)            |
+                       |                       |
+                       \______________________ |
+                                              \|
+                                               v
+                                   initrd-switch-root.target
+                                               |
+                                               v
+                                   initrd-switch-root.service
+                                               |
+                                               v
+                                          switch-root
+</programlisting>
+        </refsect1>
+
+
+        <refsect1>
                 <title>System Manager Shutdown</title>
 
                 <para>System shutdown also consists of various target