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Accepted
Chris Carter
Asked: 2012-10-28 05:56:21 +0800 CST

What does `nomodeset` do

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Since installing Ubuntu 12.10 I have been playing around trying to get my Radeon HD 5450 gpu to work with the proprietary driver, as from the start installing the driver meant losing unity.

I won't list the steps I took as it is not a requirement to answering this question.

After taking one measure and then installing fglrx-updates, upon reboot the system hung at the purple screen. So I decided to boot using nomodeset

I edited

quiet splash $vt_handoff

to look like this

quiet splash nomodeset

Making this change I am then able to log in with Unity and the proprietary driver installed and performing well. I would go as far as to say it performs better than it did in 12.04

fglrxinfo reads

display: :0  screen: 0
OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: ATI Mobility Radeon HD 5000 Series
OpenGL version string: 4.2.11903 Compatibility Profile Context

Please note the way I have added nomodeset It had been a while since I have had to do this so it was done from memory. When looking for an answer to this question I came across this and discovered that my edit was supposed to go from

quiet splash $vt_handoff

to

nomodeset $vt_handoff

What has my nomodeset edit done? The only thing wrong that I have noticed is that I don't get the plymouth Ubuntu logo screen when booting.

If that is the only trade-off I am happy to make the edit permanant.

nomodeset

2 Answers

  1. Best Answer

    The answer can be found here : http://ubuntuforums.org/showthread.php?t=1613132

    nomodeset

    The newest kernels have moved the video mode setting into the kernel. So all the programming of the hardware specific clock rates and registers on the video card happen in the kernel rather than in the X driver when the X server starts.. This makes it possible to have high resolution nice looking splash (boot) screens and flicker free transitions from boot splash to login screen. Unfortunately, on some cards this doesnt work properly and you end up with a black screen. Adding the nomodeset parameter instructs the kernel to not load video drivers and use BIOS modes instead until X is loaded.

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  2. Many open source drivers have removed support for non-kernel mode setting, so in those cases when you use nomodeset you will end up falling back to the very basic VESA un-accelerated driver. This is very much a performance and feature hit.

    nomodeset should not have any effect on the proprietary (fglrx/nvidia) drivers. They don't have this kind of kernel mode setting.

    Removing "splash" is what got rid of the Plymouth boot*splash*.

    Radeon just finished removing support for "User Mode Setting" (what nomodeset forces the computer to use) relatively recently, but with Intel graphics it has been the case for a while. http://lists.x.org/archives/xorg-announce/2012-November/002093.html

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