A Linux system can run hundreds of tasks at a time. Most of these are part of the operating system environment, but you might discover you're running a daemon or two you don't need.
Linux distributions support one of the three utilities that start daemons and services. The traditional SysV system uses scripts in /etc/init.d. The newer systemd daemon uses the same /etc/init.d scripts and also uses a systemctl call. Some distributions use Upstart, which stores configuration scripts in /etc/init.
The SysV init system is being phased out in favor of the systemd suite. The upstart utility was developed and used by Ubuntu, but discarded in favor of systemd with the 14.04 release. This chapter will focus on systemd, since that's the system used by most distributions.
