Ubuntu 16.04LTS下LG超宽屏2560×1080分辨率设置失败求助

Hey there, let's work through this resolution problem together. I've run into similar quirks with older AMD GPUs and adapter setups on Ubuntu 16.04 before, so here's a structured approach to get your LG ultrawide running at the desired specs:

First, Rule Out Hardware Limitations #

• Check your DP-to-HDMI adapter: Not all adapters support 2560×1080@60Hz. Passive adapters often cap out at 1920×1080, while active adapters handle higher resolutions. If you're using a passive one, swapping to an active DP-to-HDMI adapter might fix the issue immediately.
• Verify your LG monitor's specs: Double-check that it actually supports 2560×1080@60Hz over HDMI (most modern ultrawides do, but it's worth confirming).

Step-by-Step: Manually Add the Resolution with xrandr #

If the adapter is compatible, the problem is likely that Ubuntu isn't detecting the monitor's full resolution capabilities. Here's how to manually add the mode correctly (avoiding the display glitches you encountered earlier):

1. Generate the correct display mode timing
   Open a terminal and run:

   cvt 2560 1080 60
   

   You'll get output like this (yours might be slightly different—copy the entire Modeline line starting from the quoted name):

   2560x1080 59.98 Hz (CVT) hsync: 67.17 kHz; pclk: 230.00 MHz #

   Modeline "2560x1080_60.00" 230.00 2560 2720 2992 3424 1080 1083 1093 1120 -hsync +vsync

2. Create the new mode in xrandr
   Paste the copied Modeline content after xrandr --newmode, like:

   xrandr --newmode "2560x1080_60.00"  230.00  2560 2720 2992 3424  1080 1083 1093 1120 -hsync +vsync
   

3. Identify your DisplayPort output name
   Run xrandr without arguments to list all outputs. Look for the one marked connected (e.g., DP-1, DisplayPort-0).

4. Add the mode to your DP output
   Replace DP-1 with your actual output name:

   xrandr --addmode DP-1 "2560x1080_60.00"
   

5. Apply the mode (safely)
   If you're worried about display issues, first switch to a TTY (press Ctrl+Alt+F1) to run the command. This way, if the monitor glitches, you can easily revert:

   xrandr --output DP-1 --mode "2560x1080_60.00"
   

   If it works, switch back to the GUI with Ctrl+Alt+F7. If not, revert with:

   xrandr --output DP-1 --mode 1920x1080
   

Troubleshooting If the Mode Causes Display Glitches #

If applying the mode leads to black screens or distortion, try these fixes:

• Use gtf instead of cvt for more precise timing tailored to your monitor:

  gtf 2560 1080 60
  

  Use the generated Modeline instead of the cvt one.
• Force the mode (with caution)
  Add the --force flag to bypass EDID checks (this can damage your monitor if the timing is wrong, so only try if you're sure):

  xrandr --output DP-1 --mode "2560x1080_60.00" --force
  

• Adjust AMD Radeon Driver Settings
  Ubuntu 16.04 uses the open-source radeon driver for RV620 cards. Try adding a kernel parameter to improve compatibility:
  1. Open /etc/default/grub in a text editor:

     sudo nano /etc/default/grub
     

  2. Find the line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" and modify it to:

     GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.modeset=1 radeon.dpm=1"
     

  3. Update grub and reboot:

     sudo update-grub
     sudo reboot
     

  After rebooting, retry adding the resolution with xrandr.

Make the Resolution Persistent #

Once you get it working, save the xrandr commands to a script and set it to run on startup:

1. Create a script file (e.g., set_resolution.sh):

   nano ~/set_resolution.sh
   

2. Paste your working xrandr commands (replace with your actual mode and output):

   #!/bin/bash
   xrandr --newmode "2560x1080_60.00"  230.00  2560 2720 2992 3424  1080 1083 1093 1120 -hsync +vsync
   xrandr --addmode DP-1 "2560x1080_60.00"
   xrandr --output DP-1 --mode "2560x1080_60.00"
   

3. Make it executable:

   chmod +x ~/set_resolution.sh
   

4. Add it to Startup Applications (search for "Startup Applications" in Ubuntu's menu, click "Add", and browse to your script).

内容的提问来源于stack exchange，提问作者Nimisha