Linux – Unable to Adjust Laptop Screen Brightness

You might want to give this a try:

$ sudo echo 5 > /sys/class/backlight/acpi_video0/brightness

Change the value between 0-15 I believe to make it brighter or dimmer.

You might need to change these as well:

$ sudo echo 950 > /sys/class/backlight/intel_backlight/brightness
$ sudo echo 5 > /sys/class/backlight/acpi_video0/brightness
$ sudo echo 5 > /sys/class/backlight/acpi_video1/brightness

Changing brightness as a regular user

@JosephR. asked this folow-up in the comments and I thought it important enough to incorporate into my answer. If you want to expose this capbility to change brightness from the command line to regular users (the above echo ... > /sys/... is only accessible to root).

There is a package you can install called xbacklight which will allow user's to also change the brightness from the command line.

The package is available on Fedora and Ubuntu via repositories so just do either of these commands to install it:

# Ubuntu/Debian
$ sudo apt-get install xbacklight

# Fedora/CentOS
$ sudo yum install xbacklight

To use it:

# backlight 50%
$ xbacklight -set 50

# backlight 100%
$ xbacklight -set 100

xbacklight usage

$ xbacklight --help
usage: xbacklight [options]
  where options are:
  -display <display> or -d <display>
  -help
  -set <percentage> or = <percentage>
  -inc <percentage> or + <percentage>
  -dec <percentage> or - <percentage>
  -get
  -time <fade time in milliseconds>
  -steps <number of steps in fade>

How does user get elevated privileges to do this?

Again more follow-up to @JosephR. asking about this in a comment. It may seem like you as the user have elevated privileges to change the /sys/class/backlight/... when you use your laptops function keys (on my Thinkpad I use Fn+Home and Fn+End to change brightness). But you aren't really ever directly interacting with the /sys/class/backlight/... in the way that you think.

You're manipulating it indirectly through D-Bus. D-Bus is allowing you to manipulate this structure, org.freedesktop.Hal.Device.KeyboardBacklight, and HAL is allowing the privilege to do so. You can see this on my Fedora 14 system like this:

$ grep -i backlight /etc/dbus-1/system.d/*
/etc/dbus-1/system.d/hal.conf:         send_interface="org.freedesktop.Hal.Device.KeyboardBacklight"/>
/etc/dbus-1/system.d/hal.conf:         send_interface="org.freedesktop.Hal.Device.KeyboardBacklight"/>

In the file hal.conf:

  <!-- Only allow users at the local console to manipulate devices -->
  <policy at_console="true">
  ...
      <allow send_destination="org.freedesktop.Hal"
           send_interface="org.freedesktop.Hal.Device.KeyboardBacklight"/>

You can even mess with it from the command line via D-Bus like this. You can query the current value:

$ dbus-send \
     --print-reply \
     --system \
     --dest=org.freedesktop.Hal  \
     /org/freedesktop/Hal/devices/computer_backlight \
     org.freedesktop.Hal.Device.LaptopPanel.GetBrightness | \
     tail -1 | \
     awk '{print $2}'

Which returns the value:

15

Even cooler, you can mess with it like this (the bit int32:10 below is setting brightness to "10"):

$ dbus-send \
     --print-reply \
     --system \
     --dest=org.freedesktop.Hal  \
     /org/freedesktop/Hal/devices/computer_backlight \
     org.freedesktop.Hal.Device.LaptopPanel.SetBrightness \
     int32:10 #2&>1 > /dev/null

You can see that we changed the brightness:

$ cat /sys/class/backlight/acpi_video0/brightness
10

References

• Save brightness setting on reboot in Debian Squeeze / Wheezy
• DBUS Backlight Brightness

I struggled with a similar issue in Debian 9, installed on a Lenovo G40-30 Laptop. I went into Hibernate/Sleep and trying to initiate again the screen didn't show up although everything seemed working.

The solution is actually quite simple. It seems Linux OSs, in particular Debian and Ubuntu need at least a 4+GB swap partition for Hibernate/Sleep to work properly. If you installed with "default" configuration it will create a Swap the same size of your actual RAM (in practice a little less). So if you have a laptop with less or equal to 4 Gb RAM and installed "default" configuration, you are probably trying to solve this issue.

Swap allocation in Linux work in two ways:

1. in the form of a SWAP PARTITION in your hardrive.

2. in the form of a SWAP FILE.

YOU CAN CREATE THE SWAP FILE AS FOLLOWS:

sudo swapon --show 

shows if you have enabled the swap option. If not look up how to do this.

sudo fallocate -l 1G /swapfile

sets the size of the swap you add to 1Gb, change to the value you need.

sudo chmod 600 /swapfile        # sets the file to be owned by root     
sudo mkswap /swapfile           # mkswap tool to allocate swap in the file
sudo swapon /swapfile           # activate the swap 
sudo nano /etc/fstab            # open the file to make changes permanent

Add the line /swapfile swap swap defaults 0 0 to the file /etc/fstab:

sudo swapon --show              # show if its working
sudo free -h                    # show Memory and Swap 

IF YOU WANT TO UNDO CHANGES JUST:

sudo swapoff -v /swapfile

remove the line from /etc/fstab file: /swapfile swap swap defaults 0 0

sudo rm /swapfile         # remove the swap file

SWAP SIZES ACCORDING TO RAM:

I can indicate the following table with some recommended SWAP sizes according to your RAM. Last 3 columns are SWAP spaces:

    RAM       No hibernation    With Hibernation   Maximum

    1GB              1GB                 2GB        2GB
    2GB              1GB                 3GB        4GB
    3GB              2GB                 5GB        6GB
    4GB              2GB                 6GB        8GB
    5GB              2GB                 7GB       10GB
    6GB              2GB                 8GB       12GB
    8GB              3GB                11GB       16GB
   12GB              3GB                15GB       24GB
   16GB              4GB                20GB       32GB
   24GB              5GB                29GB       48GB
   32GB              6GB                38GB       64GB
   64GB              8GB                72GB      128GB
  128GB             11GB               139GB      256GB
  256GB             16GB               272GB      512GB
  512GB             23GB               535GB        1TB
    1TB             32GB              1056GB        2TB
    2TB             46GB              2094GB        4TB
    4TB             64GB              4160GB        8TB
    8TB             91GB              8283GB       16TB

MORE INFORMATION:

you can find thorough information on recommended SWAP sizes according to your RAM in the following link:

How much swap should I take for 1GB to 8TB of RAM on 14.04 or higher?

Credit is due for the table I added here.