升级Ubuntu17.10后xrandr提示‘output eDP-1 not found’亮度无法调节

Let's break down why you're hitting this problem and walk through practical fixes step by step:

Root Cause #

Ubuntu 17.10 switched to Wayland as the default display server (replacing Xorg). The xrandr tool is built for Xorg, so when you try using it with Wayland (where your display shows up as XWAYLAND0), it won't actually communicate with the hardware to adjust brightness—hence the "no error but no change" behavior. Also, while your brightness keys update the sysfs value, Wayland's compositor might not sync that change to the display hardware.

Solution 1: Switch Back to Xorg (Quickest Fix) #

Wayland has better security but still has compatibility gaps with some ThinkPad hardware. Here's how to revert to Xorg:

1. At the Ubuntu login screen, click the gear icon in the bottom-right corner.
2. Select Ubuntu on Xorg from the dropdown menu.
3. Log in as usual.
4. Run xrandr --listmonitors—you should see eDP-1 listed again.
5. Test your original brightness command:

   xrandr --output eDP-1 --brightness 0.7
   

Your brightness should adjust normally now, and the hardware keys should work as expected too.

Solution 2: Fix Brightness Control in Wayland #

If you want to stick with Wayland, try these steps to get brightness working:

1. First, confirm the correct backlight device path. Run:

   ls /sys/class/backlight/
   

   You'll likely see intel_backlight (common for ThinkPads).
2. Check the maximum brightness value:

   cat /sys/class/backlight/intel_backlight/max_brightness
   

   Let's say this returns 1000—use a value between 1 and this number for adjustment.
3. Adjust brightness with sudo (sysfs files require root access):

   sudo echo 500 > /sys/class/backlight/intel_backlight/brightness
   

   Note: If your brightness keys update this file but the screen doesn't change, reload the backlight kernel module:

   sudo rmmod intel_backlight && sudo modprobe intel_backlight
   

Solution 3: Update GRUB Kernel Parameters (Persistent Hardware Compatibility Fix) #

Some ThinkPads need specific kernel flags to handle brightness correctly. Here's how to set them:

1. Open the GRUB configuration file:

   sudo nano /etc/default/grub
   

2. Find the line starting with GRUB_CMDLINE_LINUX_DEFAULT and add one of these flags inside the quotes:
   • For most ThinkPads: acpi_backlight=vendor
   • If that fails, try: acpi_backlight=native
     Example modified line:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
   

3. Save the file (Ctrl+O, then Enter) and exit nano (Ctrl+X).
4. Update GRUB to apply changes:

   sudo update-grub
   

5. Reboot your system and test brightness control again.

If none of these steps work, make sure your system is fully updated (run sudo apt update && sudo apt upgrade)—sometimes a kernel or display server patch fixes these compatibility quirks.

内容的提问来源于stack exchange，提问作者Jorvis