dracut.asc: document debugging dracut on shutdown

dracut.asc

@@ -744,6 +744,23 @@ the dracut shell
 ==== Additional dracut boot parameters
 For more debugging options, see <<dracutkerneldebug>> in <<dracutcmdline7>>.
 
+
+[[debugging-dracut-on-shutdown]]
+==== Debugging dracut on shutdown
+
+To debug the shutdown sequence on systemd systems, you can _rd.break_
+on _pre-shutdown_ or _shutdown_.
+
+To do this from an already booted system:
+----
+# mkdir -p /run/initramfs/etc/cmdline.d
+# echo "rd.break=pre-shutdown" > /run/initramfs/etc/cmdline.d/debug.conf
+# touch /run/initramfs/.need_shutdown
+----
+
+This will give you a dracut shell after the system pivot'ed back in the initramfs.
+
+
 = Developer Manual
 
 == dracut Components