SysV, SystemD and UpStArt

SysV is a framework for scheduling tasks to start at boot time. It is beeing successed by systemd and upstart. This affects how services are started and stopped. With systemd you start a service like

/etc/init.d/ntp start

With SystemD you do it with

systemctl start ntp

what you want to do	how you do it with SysV	how you do it with SystemD
start service foo	/etc/init.d/foo start	systemctl start foo
stop service foo	/etc/init.d/foo stop	systemctl stop foo
find out if service foo is running	/etc/init.d/foo status	systemctl status foo
schedule service foo to start on boot	chkconfig foo on	chkconfig foo on
change "runlevel" to multi-user	init 2	systemctl isolate multi-user.target

SystemD

SystemD cannot only manage services, but also targets. Targets are sets of services. They differ from runlevels in that multiple of them can be active:

# systemctl list-units --type target | cat
UNIT                 LOAD   ACTIVE SUB    JOB DESCRIPTION
basic.target         loaded active active     Basic System
cryptsetup.target    loaded active active     Encrypted Volumes
getty.target         loaded active active     Login Prompts