• Power On - BIOS - MBR (First Sector of the Hard Disk) - Boot Loader - Kernel - initramfs - /sbin/init - Shell by getty - (X Windows System) GUI
• /sbin/init:
  • Traditionally, /sbin/init is serial processes SysVinit, did not easily take advantage of the parallel processing. Some modern methods, such as the use of containers, can require almost instantaneous startup times. Thus, systems now require methods with faster and enhanced capabilities
  • Upstart Developed by Ubuntu and first included in 2006; Adopted in Fedora 9 (in 2008) and in RHEL 6 and its clones.
  • systemd Adopted by Fedora first (in 2011); Adopted by RHEL 7 and SUSE; Replaced Upstart in Ubuntu 16.04; Replaced Upstart in Ubuntu 16.04. It has been adopted by the major distributions
  • /sbin/init now just points to /lib/systemd/systemd;

# start|stop|restart|enable|disablesudo
systemctl start|stop|restart nfs.servicesudo
systemctl enable|disable nfs.service

# Confirm
sudo ss -antlp | grep [service]
# List all available services
systemctl list-unit-files
lsof -i -P -n