Prevent brightness (both for screen and keyboard backlight) to be reset to maximum on every restart (Ubuntu on a MacBook only)

readme.md

Install

1. Copy the script to the file /usr/local/bin/save-and-restore-brightness.sh
2. Run the following command: sudo chmod a+x /usr/local/bin/save-and-restore-brightness.sh
3. Append the following line to the file /etc/pam.d/lightdm: session optional pam_exec.so /usr/local/bin/save-and-restore-brightness.sh

Note

This script can be adapted to any laptop by adjusting the variables SCREEN_BRIGHTNESS_FILE and KEYBOARD_BRIGHTNESS_FILE.

save-and-restore-brightness.sh

#!/bin/bash

SCREEN_BRIGHTNESS_FILE="/sys/class/backlight/acpi_video0/brightness"
KEYBOARD_BRIGHTNESS_FILE="/sys/class/leds/smc::kbd_backlight/brightness"

eval PAM_USER_HOME="~$PAM_USER"
CONFIG_FILE="$PAM_USER_HOME/.brightness.cfg"

case "$PAM_TYPE" in
    close_session)
        # Save
        su "$PAM_USER" -c "touch '$CONFIG_FILE'"
        echo 'SCREEN_BRIGHTNESS='$(   cat "$SCREEN_BRIGHTNESS_FILE"   )  > "$CONFIG_FILE"
        echo 'KEYBOARD_BRIGHTNESS='$( cat "$KEYBOARD_BRIGHTNESS_FILE" ) >> "$CONFIG_FILE"
        ;;
    open_session)
        # Restore
        if [ -f "$CONFIG_FILE" ]; then
            source "$CONFIG_FILE"
            if [ -n "$SCREEN_BRIGHTNESS" ]; then
                echo "$SCREEN_BRIGHTNESS"   > "$SCREEN_BRIGHTNESS_FILE"
            fi
            if [ -n "$KEYBOARD_BRIGHTNESS" ]; then
                echo "$KEYBOARD_BRIGHTNESS" > "$KEYBOARD_BRIGHTNESS_FILE"
            fi
        fi
        ;;
    *)
        if [ -z "$PAM_TYPE" ]; then
            echo "ERROR: Do not call this script directly on a shell. The script is designed to run automatically (with pam_exec)."
        fi
        ;;
esac