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Chapter 15. Shutting down, suspending, and hibernating the system

As a system administrator, you can use different power management options to manage power consumption, perform a proper shutdown to ensure that all data is saved, or restart the system to apply changes and updates.

15.1. System shutdown

To shut down the system, you can either use the systemctl utility directly, or call this utility through the shutdown command.

Using the shutdown has the following advantages:

  • You can schedule a shutdown by using the time argument. This also gives users warning that a system shutdown has been scheduled.
  • You can cancel the shutdown.

Additional resources

15.2. Scheduling a system shutdown

As a system administrator, you can schedule a delayed shutdown to give users time to save their work and log off the system. Use the shutdown command to perform the following operations:

  • Shut down the system and power off the machine at a certain time
  • Shut down and halt the system without powering off the machine
  • Cancel a pending shutdown

Prerequisites

  • Root access

Procedure

Use the shutdown command to perform any of the following tasks:

  • Specify the time at which you want to shut down the system and power off the machine: 

    # shutdown --poweroff hh:mm

    Where hh:mm is the time in the 24-hour time notation. To prevent new logins, the /run/nologin file is created 5 minutes before system shutdown.

    When you use the time argument, you can notify users logged in to the system of the planned shutdown by specifying an optional wall message, for example shutdown --poweroff 13:59 "Attention. The system will shut down at 13:59".

  • Shut down and halt the system after a delay, without powering off the machine: 

    # shutdown --halt +m

    Where +m is the delay time in minutes. You can use the now keyword as an alias for +0.

  • Cancel a pending shutdown: 

    # shutdown -c

Additional resources

15.3. Shutting down the system using the systemctl command

As a system administrator, you can shut down the system and power off the machine or shut down and halt the system without powering off the machine by using the systemctl command.

Prerequisites

  • Root access

Procedure

Use the systemctl command to perform any of the following tasks:

  • Shut down the system and power off the machine: 

    # systemctl poweroff

  • Shut down and halt the system without powering off the machine: 

    # systemctl halt
Note

By default, running either of these commands causes systemd to send an informative message to all users that are currently logged into the system. To prevent systemd from sending this message, run the selected command with the --no-wall command line option.

15.4. Restarting the system

When you restart the system, systemd stops all running programs and services, the system shuts down, and then immediately starts again. Restarting the system can be helpful in the following situations:

  • After installing new software or updates
  • After making changes to system settings
  • When troubleshooting system issues

Prerequisites

  • Root access

Procedure

  • Restart the system: 

    # systemctl reboot
Note

By default, when you use this command, systemd sends an informative message to all users that are currently logged into the system. To prevent systemd from sending this message, run this command with the --no-wall option.

15.5. Optimizing power consumption by suspending and hibernating the system

As a system administrator, you can manage power consumption, save energy on your systems, and preserve the current state of your system. To do so, apply one of the following modes:

Suspend
Suspending saves the system state in RAM and with the exception of the RAM module, powers off most of the devices in the machine. When you turn the machine back on, the system then restores its state from RAM without having to boot again. Because the system state is saved in RAM and not on the hard disk, restoring the system from suspend mode is significantly faster than from hibernation. However, the suspended system state is also vulnerable to power outages.
Hibernate
Hibernating saves the system state on the hard disk drive and powers off the machine. When you turn the machine back on, the system then restores its state from the saved data without having to boot again. Because the system state is saved on the hard disk and not in RAM, the machine does not have to maintain electrical power to the RAM module. However, as a consequence, restoring the system from hibernation is significantly slower than restoring it from suspend mode.
Hybrid sleep
This combines elements of both hibernation and suspending. The system first saves the current state on the the hard disk drive, and enters a low-power state similar to suspending, which allows the system to resume more quickly. The benefit of hybrid sleep is that if the system loses power during the sleep state, it can still recover the previous state from the saved image on the hard disk, similar to hibernation.
Suspend-then-hibernate
This mode first suspends the system, which results in saving the current system state to RAM and putting the system in a low-power mode. The system hibernates if it remains suspended for a specific period of time that you can define in the HibernateDelaySec parameter. Hibernation saves the system state to the hard disk drive and shuts down the system completely. The suspend-then-hibernate mode provides the benefit of conserving battery power while you are still able to quickly resume work. Additionally, this mode ensures that your data is saved in case of a power failure.

Prerequisites

  • Root access

Procedure

Choose the appropriate method for power saving:

  • Suspend the system: 

    # systemctl suspend

  • Hibernate the system: 

    # systemctl hibernate

  • Hibernate and suspend the system: 

    # systemctl hybrid-sleep

  • Suspend and then hibernate the system: 

    # systemctl suspend-then-hibernate

15.6. Overview of the power management commands with systemctl

You can use the following list of the systemctl commands to control the power management of your system.

Table 15.1. Overview of the systemctl power management commands

systemctl commandDescription

systemctl halt

Halts the system.

systemctl poweroff

Powers off the system.

systemctl reboot

Restarts the system.

systemctl suspend

Suspends the system.

systemctl hibernate

Hibernates the system.

systemctl hybrid-sleep

Hibernates and suspends the system.