'echo DIS > /sys/kernel/debug/vgaswitcheroo/switch' does not work

Question

I can not use echo DIS > /sys/kernel/debug/vgaswitcheroo/switch to switch to discrete ATI card. After I run the command, cat /sys/kernel/debug/vgaswitcheroo/switch still gives:

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

I use Ubuntu 11.10 amd64 arch in Lenovo Thinkpad W500. What is the matter?

Answer 1

First, you need to run the command as root.

Second , you can not re-direct output when using sudo.

So ..

1)

sudo bash -c 'echo DIS > /sys/kernel/debug/vgaswitcheroo/switch'

2) Use tee

echo 'DIS' | sudo tee /sys/kernel/debug/vgaswitcheroo/switch

Answer 2

Your change works, but it is most likely a delayed one. To make the change you should logout and re-login. This is because the change is applied after you exit X.

When Ubuntu was using Gnome desktop manager there was the gnome-session-logout command, which would do that for you. I am uncertain how to logout and re-login with Unity, which you most likely have.