about systemd: how to change default runlevel (previously using inittab)

systemd does not use /etc/inittab file to change the default runlevel.

systemd uses symlinks to point to the default runlevel. You have to delete the existing symlink first before creating a new one.

# rm /etc/systemd/system/default.target

example to switch to runlevel 3 :

# ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target

next example if you want to switch to run level 5 :

# ln -sf /lib/systemd/system/graphical.target /etc/systemd/system/default.target

another options that may apply :
poweroff.target --> runlevel 0
rescue.target    --> runlevel 1
multi.user.target --> runlevel 2,3,4
graphical.target --> runlevel 5
reboot.target --> runlevel 6

source:
http://fedoraproject.org/wiki/Systemd