You may be aware that Debian has switched from SysV to systemd as the init system. As a result systemd is the default init system for the recently released Debian 8.
This switch may have some users confused, and the aim of this article is to resolve some of those confusions.
Systemd is a System Management daemon. It is responsible for choosing the appropriate drivers upon system boot, enable network connection, start system services and bring the graphical interface upon login. On the other hand the old SysV init (which stands for ‘initialization”) just executed scripts located in the /etc/init.d directory.
There was a dire need for the successor of the aging init system. Multiple replacements were developed such as Upstart, Epoch and Mudar to tacle some of the challenges of modern systems.
The reason for the replacement is within the init daemon and the way it works. Upon system startup init is the first process started. It starts the other tasks, but one tasks starts only if the previous one has loaded successfully. As you can imagine this can cause huge delays during system boot. Systemd starts the daemons at the same time, which makes the boot process much faster.