More about systemd (ext. links)
Still under construction
These (still pending to read) links seem to point to good systemd descriptions.
systemd - System and service manager in Linux
Understanding and Using Systemd
RHEL7: How to get started with Systemd.
Systemd Essentials: Working with Services, Units, and the Journal
Understanding Systemd Units and Unit Files
systemd for administrators
http://0pointer.de/blog/projects/systemd-for-admins-1.html
http://0pointer.de/blog/projects/systemd-for-admins-2.html
http://0pointer.de/blog/projects/systemd-for-admins-3.html