Anyone know how to access RasPi GPIO without sudo?

I think the proper way is to use a somewhat standard DAQ system like Comedi for most applications that don't need realtime response. I'm working on a GPIO/Gertboard kernel module the uses the Comedi library for DIO, analog and PWM. I hope to have it in the 3.7ish kernel release but it works with the current RPi debian 3.2 release with some easy changes.

The code is still pretty alpha but the basic DIO code framwork is done.

daq-gert https://github.com/nsaspook/daq_gert.git

http://www.comedi.org/

Here is a HOWTO to test the daq_gert module. It's still in development but most of the DIO function code is in place with fake analog devices as placeholders for now.

https://github.com/nsaspook/daq_gert/blob/master/RPi_Comedi_HOWTO.txt

Roger Wolff wrote:

 

Now back to your problem...
If you make a little program that allows you to manipulate just the GPIO outputs, that won't allow you to cause all the other mischief you'd be able to make with "/dev/mem" access, then you can install that program with superuser permissions (setuid) and then you can use that program as a normal user.

 

I have written such a program. IIRC, it is contained in this package:

http://www.bitwizard.nl/software/gpio_spi_i2c_20120419.tgz

 

The program can be made setuid by doing:

  sudo chown root <program name>

  sudo chmod 4755 <program name>

jopaji wrote:

 

Keith Chiem wrote:

 

$ sudo chown pi /dev/mem

That will not work.  As well as any access controls imposed by the filesystem, you also need to have capability CAP_SYS_RAWIO to open the /dev/mem device.  So you do need to be setuid root (or setcap).

 

Note that you do not need any special permissions for any of the later steps, however.  So you can start as root, open /dev/mem, drop privileges with set(res)uid, mmap just the registers you need, close the device to make it impossible to map any more, and then continue with the rest of your code safely.

Well, I finally got around to testing these suggestions.  I got CAP_SYS_RAWIO to work (mostly), but decided that it was too dangerous.  So I went with a combination of Roger's suggestion to use chown and chmod so that my programs starts as root, and jopaji's suggestion to call setuid(getuid()) to drop superuser access after using mmap() so as to become a normal user.

This scheme is also described by nroff-man at the Raspberry Pi Forum: http://www.raspberrypi.org/forums/viewtopic.php?f=29&t=22515

I also learned that you should close /dev/mem once you have done the mmap() so that you don't have a dangerous file descriptor lying around.  Here's my final code, which sets global pointer RasPiGPIO to the virtual address of the GPIO registers or NULL on failure:

// Attempt to map RasPi GPIO registers to a virtual address.

// Set RasPiGPIO to that address, or NULL if unable to map (print warning).

static void AccessRasPiGPIO(void)

{

    int fd = open("/dev/mem", O_RDWR);

    if (fd < 0)

    {

        fprintf(stderr, "Cannot access Raspberry Pi GPIOs: you probably need sudo.\n");

        return;

    };

    // 0x20200000 is the Debian base for mapping RasPi GPIOs using /dev/mem.

    RasPiGPIO = mmap(NULL, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0x20200000);

    if (RasPiGPIO == MAP_FAILED)

    {

        fprintf(stderr, "Cannot access Raspberry Pi GPIOs: mmap() failed.\n");

        RasPiGPIO = NULL;

    } else printf("XXICC can access Raspberry Pi GPIOs.\n");

    close(fd);    // No longer need /dev/map once we have the virtual address.

}

After I call this function, I set the user ID back to the original user with the code: setuid(getuid());

Thank you to everyone for their suggestions!

If you are the only one with access it is no real problem. I don't particularly wish to give sudo access to the kids.