Basically, Linux used to have a bunch of random programs made by random people that did random things that Linux users needed their computers to use.
-need to synchronize network time?
-need to get an IP address?
-need to schedule a program to execute once a week?
-need to write system logs somewhere?
There are random programs written by random people to do all of that, and they were called by shell scripts that executed them in the original Linux init daemons.
What systemd did is, it made a very excellent init daemon that used this trick with sockets that allowed it to start all services at once, making the computer boot really fast.
If it had stopped at that, people would have loved it.Post too long. Click here to view the full text.