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Old 12-20-2005, 05:48 PM   #1
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ioctl as non-root user

I'm trying to get my keyboard leds (numlock, capslock, etc.) to blink and after some searching I found this can be done by using an ioctl function:

int fd = open( "/dev/console", O_RDWR | O_NOCTTY );
int led = LED_NUM;
ioctl( fd, KDSETLED, led );
At first it didn't work, but after a lot of time wasted, I found out it does work when run as root.

I tried changing permissions and ownership of /dev/console, but no luck.

I know there are some (X related) alternatives, and some ways to use fake keypresses, but I don't want that. I just want to know if there's any way to use the ioctl without being root. I even don't mind to patch my kernel if I knew where to change the code.

If anyone could help, I would be very grateful. Thanks in advance.
Old 12-20-2005, 09:13 PM   #2
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Try with /dev/tty
See the great article at
Old 12-20-2005, 09:53 PM   #3
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Easiest would be to create a helper program that just does the LED stuff and make it setuid.
Old 12-21-2005, 03:02 AM   #4
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Thanks, but I already found that page (I've searched for hours in Google). I tried all kinds of devices, all kinds of open flags and no luck. In fact, if you look closely, you'll see that in the SET example, the author uses /dev/console also.


Not very elegant, but a possibility.

What I still don't know, is if it's the kernel that denies the command from any program that isn't root (only solution is to patch), or if the problem lies soomewhere else.

Does anyone know something more about this?


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