Halt, reboot, and power off the system

Just like their names imply, halt, reboot, and poweroff commands are used to halt, reboot, and power off the system. These commands behave differently on different Linux distributions, but the general behaviour is:

• halt – shuts down the system without powering it off.
• reboot – initiates a reboot sequence.
• poweroff – shuts down the system and turns of the power. This is roughly equivalent to pressing the power button on your computer.

Not that these commands are not widely used anymore. You should use the shutdown command instead because it supports a time-delayed shutdown and sending of a warning message. You can also use various options with the shutdown command to specify whether to halt, reboot, or power off the system.