Ubuntu – How to disable ATI discrete graphic GPU at startup in Ubuntu 14.04 without BIOS

this worked for me (hybrid with i915 - radeon redwood (5000), ubuntu 11.10 64, unity)

most laptop "hybrid equiped" boot with both gpu ON (could explain why batteries last so few with a fresh install of ubuntu and default GRUB settings), but with IGD (i915) connected (seems to be by default with no BIOS tweak)

Well, lets say your're allready logged in Unity (or Gnome):

Just want to power off DIS to save your batt (you'll probably gain about 30 to 40%+ time) ? issue that in a terminal

echo "OFF"|sudo tee /sys/kernel/debug/vgaswitcheroo/switch

But I can guess your're waiting for more than that... switch from IGD to DIS!

Ok, read : first logoff unity... yes, you need!

open another terminal with

CRTL-ALT-F1

login and stop lightdm (on which runs the Unity shell)

sudo service lightdm stop

connect discret gpu (right after pressing ENTER, your screen may flicker... that sounds good! or it may ... just freeze! depend your setup.

echo "DDIS"|sudo tee /sys/kernel/debug/vgaswitcheroo/switch

verify the status

sudo cat /sys/kernel/debug/vgaswitcheroo/switch

should get

0:IGD: :Off:0000:00:02.0
1:DIS:+:Pwr:0000:01:00.0

then what you need is start the lightdm-Unity GUI

sudo service lightdm start

At that point you should get a regular Ubuntu 11 login screen, if not, try pressing

CRTL-ALT-F7 and login running on the DIS GPU

if it don't work, your computer may have frozen. Try back

CRTL-ALT-F1

to get the terminal and restart.

If you succeed to connect and use your DIS GPU, you will switch back to default both gpu ON with IGD connected setting next time you'll restart...

That's a really poor hybrid GPU switch support... but it works. Should be possible to force your prefered GPU setting during boot, just after vgaswitcheroo is available and before lightdm starts.

Better could be with GRUB and menu choice... if anyone knows how to?

Greater could be a script to run inside Unity... I'm afraid it'll be hard to do, because lightdm must be restarted!

A simplistic way would be to add echo OFF > /sys/kernel/debug/vgaswitcheroo/switch to /etc/rc.local before the exit 0 so it looks like this:

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

echo OFF > /sys/kernel/debug/vgaswitcheroo/switch

exit 0