Prerequisites

Switch on a physical server or a virtual machine (in this case, type: # virsh start vm).
Connect to the console.

Basic Management

To reboot the system, choose one command among these:

# reboot
# systemctl reboot
# shutdown -r now
# init 6
# telinit 6

To shutdown the system, choose one command among these:

# halt
# systemctl halt
# shutdown -h now
# init 0
# telinit 0

To switch off the system, choose one command among these:

# poweroff
# systemctl poweroff

Advanced Management

To suspend the system, type:

# systemctl suspend

To put the system into hibernation, type:

# systemctl hibernate

To put the system into hibernation and suspend it, type:

# systemctl hybrid-sleep

Additional Resources

Bob Cromwell provides some very interesting pages about Linux kernel details and the Linux boot process.