Arch Linux

iscream

Member

Registered: 2010-03-26

Posts: 4

Access denied while undervolting

I try to undervolt my CPU. Therefor, I found out the possible VIDs I want to use through phc-tool. Now I want to store those values, but I'm not able to do so:

[jaguan@arch-laptop ~]$ echo 37 27 10 > /sys/devices/system/cpu/cpu0/cpufreq/phc_vids 
bash: /sys/devices/system/cpu/cpu0/cpufreq/phc_vids: Keine Berechtigung

I also tried the alternative from the german archwiki:

[jaguan@arch-laptop ~]$ echo "10:37 8:32 6:10" > /sys/devices/system/cpu/cpu0/cpufreq/phc_controls 
bash: /sys/devices/system/cpu/cpu0/cpufreq/phc_controls: Keine Berechtigung

So it returns that I have no permissions to execute these commands. But also with sudo it still does not work. What can I do?

Rorschach

Member

From: Ankh-Morpork

Registered: 2008-11-07

Posts: 143

Re: Access denied while undervolting

No, this doesn't work with sudo because just the echo and not the pipe will run with root-rights. But you can use tee for it e.g. :

$ echo "10:37 8:32 6:10" | sudo tee > /sys/devices/system/cpu/cpu0/cpufreq/phc_controls

or start a root-shell with

$ sudo su

then your command works too or you do it with bash:

$ sudo bash -c  "echo "10:37 8:32 6:10" > /sys/devices/system/cpu/cpu0/cpufreq/phc_controls"

or...

endless possibilities...

PS: This is not a Kernel & Hardware issue but a shell issue

Last edited by Rorschach (2010-03-26 14:52:36)

iscream

Member

Registered: 2010-03-26

Posts: 4

Re: Access denied while undervolting

Thank you!!!
That works well. But I got another problem. In phc-tool, I tried to get VIDs below 19 for some frequencies. I can adjust them in phc-tools but the analyze-tab tells me that the cpu only lowers the VIDs to 19. What is the problem in this case?