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使用 Ubuntu 18.04 降低屏幕最大亮度

tag-icon • tag-icon 18.04 laptop screen brightness backlight
使用 Ubuntu 18.04 降低屏幕最大亮度

我正在尝试为运行 Ubuntu 18.04 的 Thinkpad X250 设置最大屏幕亮度限制。

一些背景信息： 我把原来的屏幕换成了新的（在安装 Ubuntu 之前），亮度控制工作正常，但我注意到，亮度超过 55-60% 时，人眼几乎察觉不到变化，但它会消耗更多电池，并且开始变得非常热。我打算把这台电脑送给家里的年轻和没有经验的用户，所以我想设置一个限制，不需要用户在每次启动时采取行动，并且可以适用于所有用户，而不必担心通过软件管理器进行更新会删除设置。

我尝试过： 我尝试直接编辑/sys/class/背光/intel_backlight/max_brightness但它拒绝编辑（即使使用 chmod 更改权限）。我看到一些答案告诉我要添加如下命令“回显 MAX_VALUE > /sys/class/backlight/intel_backlight/max_brightness”在/etc/rc.local，但我没有这个文件。请注意，我没有 *acpi_** 文件或文件夹/sys/class/背光/。

设置所有用户永久亮度限制的正确方法是什么？

答案1

我编写了一个脚本来监视/sys/class/backlight/*/brightness并重定向它：如何在 `/sys/class/backlight` 中切换选项来解决亮度问题？。

只需添加三行即可快速修改以满足您的需要：

    # Modification for: https://askubuntu.com/questions/1051171/lowering-screen-max-brightness-with-ubuntu-18-04
    # If brightness > 50, set to 50
    [[ WatchPer -gt 50 ]] && WatchPer=50

修改后的redirected-brightness脚本

#!/bin/bash

# NAME: redirect-brightness
# PATH: /usr/local/bin
# DESC: Redirect to correct driver when Ubuntu is adjusting the wrong
#       /sys/class/DRIVER_NAME/brightness

# DATE: June 13, 2018. Modified June 14, 2018.

# NOTE: Written for Ubuntu question:
#       https://askubuntu.com/q/1045624/307523

WatchDriver="/sys/class/backlight/intel_backlight"
PatchDriver="/sys/class/backlight/intel_backlight"

# Must be running as sudo
if [[ $(id -u) != 0 ]]; then
    echo >&2 "Root access required. Use: 'sudo redirect-brightness'"
    exit 1
fi

# inotifywait required
type inotifywait >/dev/null 2>&1 || \
    { echo >&2 "'inotifywait' required but it's not installed.  Aborting."; \
      echo >&2 "Use 'sudo apt install inotify-tools' to install it.'"; \
      exit 1; }

# Was right watch driver directory name setup correctly?
if [[ ! -d $WatchDriver ]]; then
    echo >&2 "Watch directory: '$WatchDriver'"; \
    echo >&2 "does not exist. Did you spell it correctly? Aborting.'"; \
    exit 1;
fi

# Was right patch driver directory name setup correctly?
if [[ ! -d $PatchDriver ]]; then
    echo >&2 "Redirect to directory: '$PatchDriver'"; \
    echo >&2 "does not exist. Did you spell it correctly? Aborting.'"; \
    exit 1;
fi

# Get maximum brightness values
WatchMax=$(cat $WatchDriver/max_brightness)
PatchMax=$(cat $PatchDriver/max_brightness)

# PARM: 1="-l" or "--log-file" then write each step to log file.
fLogFile=false
if [[ $1 == "-l" ]] || [[ $1 == "--log-file" ]]; then
    fLogFile=true
    LogFile=/tmp/redirect-brightness.log
    echo redirect-brightness LOG FILE > $LogFile
    echo WatchMax: $WatchMax PatchMax: $PatchMax >> $LogFile
fi

SetBrightness () {
    # Calculate watch current percentage
    WatchAct=$(cat $WatchDriver/actual_brightness)
    WatchPer=$(( WatchAct * 100 / WatchMax ))
    [[ $fLogFile == true ]] && echo WatchAct: $WatchAct WatchPer: $WatchPer >> $LogFile
    # Reverse engineer patch brightness to set
    # Modification for: https://askubuntu.com/questions/1051171/lowering-screen-max-brightness-with-ubuntu-18-04
    # If brightness > 50, set to 50
    [[ WatchPer -gt 50 ]] && WatchPer=50
    PatchAct=$(( PatchMax * WatchPer / 100 ))
    echo $PatchAct | sudo tee $PatchDriver/brightness
    [[ $fLogFile == true ]] && echo PatchAct: $PatchAct >> $LogFile
}

# When machine boots, set brightness to last saved value
SetBrightness

# Wait forever for user to press Fn keys adjusting brightness up/down.
while (true); do
    inotifywait --event modify $WatchDriver/actual_brightness
    [[ $fLogFile == true ]] && \
        echo "Processing modify event in $WatchDriver/actual_brightness" >> $LogFile
    SetBrightness
done

答案2

由于这是一个 Linux 内核只读值，因此无法按照您想要的方式完成此操作：

没有代码可以读取该值max_brightness并对其采取行动：内核只是发布硬件的最大值。

如果您尝试强制内核仍然接受写入，它将抛出一个Input/output error。

也许有一种方法可以：

  • 拦截单独的按键，然后拒绝更高，但这意味着发布新问题并在这里再次说明为什么要这么做。
  • 要求 Linus Torvalds 本人处理你的错误，但他近期解决这个问题的可能性很小......;-)

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