How to make my raspberry pi consume less when used both as desktop and idle server ???

2 minute read Published: 2025-04-02

Ok something that deserves a little post

My problem:

I'm sometimes using my raspberry pi 400 (equivalent to pi 4b) on a 2 monitors setup (CRT because I'm a cool kid) : one to watch movies / TV Shows, the other to write some shit, which requires a bit of performance because I like it to be responsive

And sometimes it needs to act as a low power server, then it's mostly idle at least doesn't require that much power, and since it's powered most of the time by a solar panel, I'd like it to be... as power saving as possible.

My idea:

Using keyboard shortcut to switch it to low power, or high power depending on what we need

On low power:

  • I want the frequency of the cpu to be as low as possible
  • I want the USB to autosuspend quickly
  • I want both my hdmi to be turned off
  • I don't want any graphical apps

On high power:

  • Frequency set to on demand
  • USB always on
  • Both HDMI must be on
  • I need graphical apps

I went with three scripts

One to turn everything off:

#!/bin/bash

systemctl stop lightdm # bye bye graphic apps
cpufreq-set -g powersave # low frequencies... everywhere ! (could be useless thanks to powertop)
systemctl start powertop 
powertop --auto-tune # will try to tune everything to low power
/usr/bin/vcgencmd display_power 0 2 #switch off HDMI 0
/usr/bin/vcgencmd display_power 0 7 #switch off HDMI 1

One to turn everything on:

/usr/bin/vcgencmd display_power 1 2 #switch on HDMI 0
/usr/bin/vcgencmd display_power 1 7 #switch on HDMI 1 
cpufreq-set -g performance # high frequencies !
systemctl stop powertop
systemctl start lightdm # back to UI
echo 'on' > '/sys/bus/usb/devices/1-1.3.1/power/control' # manually setting some usb devices to on
echo 'on' > '/sys/bus/usb/devices/1-1.2/power/control' # manually setting some usb devices to on
echo 'on' > '/sys/bus/usb/devices/1-1.1/power/control' # manually setting some usb devices to on
cpufreq-set -u 1.80GHz # need to reset max frequency to my max raspi freq, you can check yours with cpufreq-info

One to monitor keyboard inputs:

#!/bin/bash

# Path to your keyboard event device
KEYBOARD_DEVICE=$1 # mine was "/dev/input/event5"

# Path to the script you want to execute
ON_SCRIPT="/home/salcie/turn_on.sh"

OFF_SCRIPT="/home/salcie/turn_off.sh"
# Monitor key events and execute the script when f7 or f8 is pressed
sudo evemu-record "$KEYBOARD_DEVICE" | while read -r event; do
    echo "key "$event
    if [[ $event == *"EV_KEY"* && $event == *"KEY_F7"* && $event == *" 0000"* ]]; then
        echo "F7 key pressed. Turning on !"
        timeout 30 "$ON_SCRIPT" &
    fi
    if [[ $event == *"EV_KEY"* && $event == *"KEY_F8"* && $event == *" 0000"* ]]; then
        echo "F8 key pressed. Turning off..."
        timeout 30 "$OFF_SCRIPT" &
    fi
done

the script needs your input keyboard as argument for example

./monitor.sh /dev/input/event5

you can find it out with evtest

That's it... I guess

Will need to remember sources...

maybe those:

=> https://askubuntu.com/questions/185274/how-can-i-disable-usb-autosuspend-for-a-specific-device

=> https://www.reddit.com/r/raspberry_pi/comments/jyvj5q/comment/mfutkmo/