Access GPIO (/sys/class/gpio) as non-root

bash raspberry-pi chmod chown raspberry-pi2
TiMESPLiNTER picture TiMESPLiNTER · Jun 19, 2015 · Viewed 12.5k times · Source

The /sys/class/gpio can only be access as root by default. So I like that a new group gpio can use the files and directories under /sys/class/gpio. To achieve that I added the following lines to /etc/rc.local (I'm on Debian):

sudo chown root:gpio /sys/class/gpio/unexport /sys/class/gpio/export
sudo chmod 220 /sys/class/gpio/unexport /sys/class/gpio/export

So this gives write permissions to all the gpio group members. So they can now export and unexport pins fine.

The problem is they can't read/write the specific pin files after export (e.x. /sys/class/gpio/gpio17) beacause those are owned by root:root again.

How can I change that they are created by default as root:gpio too? I mean I can do that manually each time I export a pin. But that's a bit uncomfy.

UPDATE

According to larsks' answer I created the missing rule file. Now it partially works:

-rwxrwx---  1 root gpio 4096 Jun 19 16:48 export
lrwxrwxrwx  1 root gpio    0 Jun 19 16:51 gpio17 -> ../../devices/soc/3f200000.gpio/gpio/gpio17
lrwxrwxrwx  1 root gpio    0 Jun 19 16:45 gpiochip0 -> ../../devices/soc/3f200000.gpio/gpio/gpiochip0
-rwxrwx---  1 root gpio 4096 Jun 19 16:45 unexport

But for the ./gpio17/ I still get root:root:

-rw-r--r-- 1 root root 4096 Jun 19 16:52 active_low
lrwxrwxrwx 1 root root    0 Jun 19 16:52 device -> ../../../3f200000.gpio
-rw-r--r-- 1 root root 4096 Jun 19 16:52 direction
-rw-r--r-- 1 root root 4096 Jun 19 16:52 edge
drwxr-xr-x 2 root root    0 Jun 19 16:52 power
lrwxrwxrwx 1 root root    0 Jun 19 16:52 subsystem -> ../../../../../class/gpio
-rw-r--r-- 1 root root 4096 Jun 19 16:52 uevent
-rw-r--r-- 1 root root 4096 Jun 19 16:52 value

UPDATE 2

Okay I solved the problem. Because I installed Raspbian over the RaspbianInstaller I never went through the raspi-config tool. This seems to be a problem. Because I was also missing the /sys/device/virtual/gpio/ folder.

I followed this guide here: http://www.element14.com/community/message/139528/l/re-piface-digital-2--setup-and-use#139528

And afterwards the permissions were correct (even for the pin-folders and their files value, direction, ...).

Answer

Roman Savrulin picture Roman Savrulin · Jun 1, 2018

More common rule for 4.x kernels will be the following

SUBSYSTEM=="gpio*", PROGRAM="/bin/sh -c 'find -L /sys/class/gpio/ -maxdepth 2 -exec chown root:gpio {} \; -exec chmod 770 {} \; || true'"

The rule in the initial answer will fail to chown the exported gpio if there's a symbolic link in the path

UPD please beg in mind that when you export some GPIO via sysfs, you should wait for udev rule to fire and complete before you get desired access rights. The thing that worked for me was sleep about 100ms before trying to access GPIO files.

Related questions

How to concatenate string variables in Bash

In PHP, strings are concatenated together as follows: $foo = "Hello"; $foo .= " World"; Here, $foo becomes "Hello World". How is this accomplished in Bash?

Read More
How can I check if a directory exists in a Bash shell script?

What command can be used to check if a directory exists or not, within a Bash shell script?

Read More
How do I tell if a regular file does not exist in Bash?

I've used the following script to see if a file exists: #!/bin/bash FILE=$1 if [ -f $FILE ]; then echo "File $FILE exists." else echo "File $FILE does not exist." fi What's the correct syntax to use if I only want …

Read More