How to save power consumption in Linux

Powertop is a great tool to save battery power and with the help of another tool, acpid, to observe the acpi event and configure it automatically.

Acpid comes with predefined actions for triggered events. By default, these actions are defined in /etc/acpi/handler.sh

The action “ac_adapter” has a default option

*)
                logger "ACPI action undefined: $2"

So, whether or not you are plugged in the ac, you can see the log with:

journalctl -f

ene 12 20:54:49 msi root[3888]: ACPI action undefined: ACPI0003:00

In this case you must to change the /etc/acpi/handler.sh with:

ac_adapter)
        case "$2" in
            ACPI0003:00)

Saving the changes and unplug the ac, the following appears in the log:

ene 12 21:00:31 msi root[6101]: AC unpluged

The change works. Now you can add the powertop commands. This is my handler.sh:

ac_adapter)
        case "$2" in
            ACPI0003:00)
                case "$4" in
                    00000000)
                        powertop --auto-tune
                        echo 'on' > '/sys/bus/usb/devices/3-2/power/control' # USB USB Receiver [Logitech]
                        echo 'enabled' > '/sys/class/net/wlo1/device/power/wakeup'
                        echo 'enabled' > '/sys/bus/usb/devices/usb1/power/wakeup'
                        echo 'enabled' > '/sys/bus/usb/devices/usb2/power/wakeup'
                        echo 'enabled' > '/sys/bus/usb/devices/usb3/power/wakeup'
                        echo 'enabled' > '/sys/bus/usb/devices/usb4/power/wakeup'
                        echo 'enabled' > '/sys/bus/usb/devices/3-2/power/wakeup'
                        echo 'enabled' > '/sys/bus/usb/devices/3-5/power/wakeup'
                        echo 'enabled' > '/sys/bus/usb/devices/3-10/power/wakeup'
                        logger 'AC unpluged'
                        ;;
                    00000001)
                        echo 'disabled' > '/sys/class/net/wlo1/device/power/wakeup'
                        echo 'disabled' > '/sys/bus/usb/devices/usb1/power/wakeup'
                        echo 'disabled' > '/sys/bus/usb/devices/usb2/power/wakeup'
                        echo 'disabled' > '/sys/bus/usb/devices/usb3/power/wakeup'
                        echo 'disabled' > '/sys/bus/usb/devices/usb4/power/wakeup'
                        echo 'disabled' > '/sys/bus/usb/devices/3-2/power/wakeup'
                        echo 'disabled' > '/sys/bus/usb/devices/3-5/power/wakeup'
                        echo 'disabled' > '/sys/bus/usb/devices/3-10/power/wakeup'
                        logger 'AC pluged'
                        ;;

Remember, this doesn’t work if you start the laptop without an ac. How do you solve it?
Inspired by the following post I created a new systemd unit:

/usr/lib/systemd/system/acpid-boot.service

[Unit]
Description=ACPI boot handle
Documentation=man:acpid(8)

[Service]
Type=oneshot
ExecStart=/usr/local/sbin/acpi-boot-handle.sh

[Install]
WantedBy=multi-user.target

And the script /usr/local/sbin/acpi-boot-handle.sh contains:

#!/usr/bin/env bash
set -euo pipefail

if [[ $(acpi -a | grep on) ]]
then
        onBit=1
else
        onBit=0
fi
/etc/acpi/handler.sh ac_adapter ACPI0003:00 foo 0000000$onBit

In this way you simulate the acpi action when the laptop starts.

In my case a MSI Modern 14 the battery has 3 hours more when all of the powertop options are enabled.