Power and Sleep

• The process of shutting down the system involves the orderly termination of all the processes on the system, as well as performing some vital housekeeping chores (such as syncing all of the mounted filesystems) before the system powers off

Power off

• Performs full orderly shutdown and completely cuts physical electricity to the machine

sudo poweroff
 
# modern equivalent in systemd
sudo systemctl poweroff

Halt

• Legacy concept, used to suspend CPU but leave motherboard powered on
• Note: The old shortcut sudo halt defaults to a full power off on modern systems, but systemctl halt will execute a true software-only freeze

sudo halt
 
# modern equivalent in systemd
sudo systemctl halt

Reboot

• Performs full orderly shutdown and instantly restarts the computer hardware

sudo reboot
 
# modern equivalent in systemd
sudo systemctl reboot

Shutdown

• Legacy Command Wrapper

# Shuts down and powers off immediately (-h is treated as poweroff)
sudo shutdown -h now
 
# reboot
sudo shutdown -r now
 
# Schedule a power off in 10 minutes with a message
sudo shutdown +10 "Maintenance time!"

Suspend

• aka Sleep mode
• computer enters a low-power state and system state stay entirely inside your physical RAM
• System turns off the screen, hard drives, and CPU, but must keep a tiny stream of electrical power running to your RAM chips

sudo systemctl suspend

Hibernate

• aka Deep Sleep mode
• saves entire system state on HDD/SSD (swap space)
• No power needed

sudo systemctl hibernate

Uptime

• how long system has been running since last boot

uptime