[SOLVED] Sending command to /sys/... or /proc/acpi/...

Geriao · 03-15-2010, 08:47 AM

There were a couple occasions where I want to send commands to "files" in these locations:

To increase/decrease the brightness level on a Compaq Presario laptop, but issuing "echo 20 > /proc/acpi/video/.../brightness"
To make a Dell Inspiron 1525 laptop suspend to ram, by issuing "echo mem > /sys/power/state"

If I try one of these just like that, I get a "Permission denied". Yet, even if I use "sudo echo mem > /sys/power/state", I still get the same error.

But if I put this line of code in a bash script then run it with sudo, it works.

Is that a bug? Why can't I sudo it from the terminal?

neonsignal · 03-15-2010, 10:02 PM

The reason is that the redirection is being done on the output of 'sudo echo mem', at which point it only has user privileges (redirection is a shell function, not a function of the echo). If you need to do it from the command line, one way is to start a shell under sudo:

Code:

sudo bash -c 'echo mem >/sys/power/state'

Geriao · 03-16-2010, 06:37 AM

That explains it!
Thanks!!