GPIO access from user space

Mabzy · August 22, 2016

Hi

Can any one tell me how to access the GPIO from user space, I have tried this:

sudo echo 203 > /sys/class/gpio/export

But get this result

-bash: /sys/class/gpio/export: Permission denied

It's of course some thing really simple, but I haven't been able to find any thing which can lead in the right direction.

I have tried adding user account to the /etc/sudoers

By inserting this:

# See sudoers(5) for more information on "#include" directives:

#includedir /etc/sudoers.d

mabzy ALL=(ALL) NOPASSWD: ALL

martinayotte · August 22, 2016

This is because the "sudo" command apply only to the "echo", not to the redirection of the output.

Try the following instead :

sudo su - -c "echo 203 > /sys/class/gpio/export"

tkaiser · August 22, 2016

Please compare with http://forum.armbian.com/index.php/topic/1851-rfc-make-armbian-more-iot-friendly/

Might be worth a try adding a group gpio, adding your user to this group and putting

chown -R root:gpio /sys/class/gpio && chmod -R 770 /sys/class/gpio

into /etc/rc.local prior to "exit 0". Adding group gpio and a user to it should be possible this way:

sudo su -
addgroup gpio
usermod -aG gpio ${SUDO_USER}

(log out and in afterwards)

Mabzy · August 22, 2016

Thanks it works , but is there away to grant user space access so that I can access the gpio's like this from user space:

echo 203 > /sys/class/gpio/export

Mabzy · August 22, 2016

Thanks tkasier

Your answer was crossing with my reply to martinayotte

But also thanks to martinayotte

Last one - where can I find UART -> ttyXX mappings ?

martinayotte · August 22, 2016

What do you mean by ttyXX mappings ?

The port numbers such /dev/ttyS0 are corresponding to uart0 defined in FEX for Legacy or DTS for Mainline.

Mabzy · August 23, 2016

Thanks - I was referring to what device the uart0 was assigned to.

Will Allen · May 17, 2017

On 8/22/2016 at 1:20 PM, tkaiser said:
Please compare with http://forum.armbian.com/index.php/topic/1851-rfc-make-armbian-more-iot-friendly/

Might be worth a try adding a group gpio, adding your user to this group and putting
chown -R root:gpio /sys/class/gpio && chmod -R 770 /sys/class/gpio
into /etc/rc.local prior to "exit 0". Adding group gpio and a user to it should be possible this way:
sudo su -
addgroup gpio
usermod -aG gpio ${SUDO_USER}
(log out and in afterwards)