Systemd journald logging before /sbin/init?

Question

dear arch experts---I understand that I have an initrd stage that eventually invokes /sbin/init (which is systemd) on a switch_root.  the initrd stage can echo various log information, too.  so, now I am curious: how can the pre-systemd process log output be logged to journald?  can the pre-systemd initrd write to an area of RAM that survives the switch_root and will then be picked up by journald as soon as journald becomes available? 
sincerely,  /iaw

Answer 1

Probably this:
In this page we attempt to roughly describe the interfaces that exist between the initrd and systemd. These interfaces are currently used by dracut and the ?ArchLinux initrds.
- The initrd should mount /run as a tmpfs and pass it pre-mounted when jumping into the main system when executing systemd. The mount options should be mode=755,nodev
http://www.freedesktop.org/wiki/Softwar … Interface/
Would have to re-check the mkinitcpio sources (bash scripts) to see how it "passes over".
There's even more information logged, before systemd actually starts, e.g. from Kernel. (http://0pointer.de/blog/projects/journalctl.html)
You can see that in your log, there's alot of information before:
[...] systemd[1]: systemd 217 running in system mode. (+PAM -AUDIT -SELINUX -IMA -APPARMOR [...]