Overview of Power Management in Linux

How to perform various power management related tasks in a Linux system such as:- 

1.  halt
2. power-off
3. shutdown
4. reboot 
5.  sleep (suspend)
6.  hibernate
7. hibernate-sleep 

Essential power management options:

Comparing Halt, power-off, Shutdown, and Reboot:

Mode/State	What does it do?	What does it not do?
Halt	Terminate all processes and services and shutdown CPU but leaves the system in a powered-on state.	Does not power-off the system.
Power-off	Turn off all services and process then send an ACPI command to the motherboard and then to the PSU to terminate the power supply of the system.	Does not execute any command or script before turning off the system.
Shutdown	Execute configured commands and scripts and then shuts down the system by following the same process which the power-off mode uses.	Does not keep the system in a powered-on state.
Reboot	First shutdown the system by following the same process which the shutdown mode uses then sends a reboot ACPI command to the motherboard and PSU to start the system again.	Does not keep the system in a powered-off state.

Key Points, Need to Know:

• In modern Linux, the systemd utility is used to manage all services and processes of the system.

• In systemd, the halt, poweroff, and reboot commands have been replaced with the systemctl halt, systemctl poweroff, and systemctl reboot commands respectively.

• For compatibility reasons the halt, poweroff, and reboot commands still exist but they are linked with their newer versions.

• For example, if you run the halt command, the systemd will execute the systemctl halt command.

You can try these commands 

•command halts the system.

•#shutdown -H now

•command powers off the system.

•#shutdown -P now

•command shuts down the system.

•#shutdown

•command reboots the system.

•#shutdown -r now

•command shuts down and powers off the system at 03:44 AM.

•#shutdown -P 03:44

•command halt the system after 10 minutes.

•#shutdown -H 10

•command reboots the system after 15 minutes.

•#shutdown -r 15

Advanced Power Management options:

                                                                                                                                                               

 Thanks By Harihar Mishra

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