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I'm building a system, using buildroot, that will have a webpage to control a raspberry's GPIO pins, using php. To do so, I'm writing (and reading) the kernel files located in /sys/class/gpio/.. the problem is that apache doesn't have permission to write or read in such directories and files. I can make it work by changing all directories permissions to:

chmod a+rx dir_name

But this has to be executed everytime the system is turned on since that the /sys/... permissions are reset to default when the system is turned off.

So I would like to know what's the easiest way to solve this problem? Not forgetting that at some point I might write into /sys/class/gpio/export a GPIO number creating a new directory (/sys/class/gpio/gpioN/ where N is the pin number) with new files wich permissions need to be changed aswell.

I'm not very skilled in this kind of stuff but the only way I can think of making it work is to run a script at boot that would export all GPIO pins (write in /sys/class/gpio/export) and then change the permissions of all directories and files. The problem is that I have no clue how to do such scripts, besides that it needs to be in /etc/init.d directory. I've looked in some of the files in this directory but can't understand them, what language is it written?

EDIT 1

I found in a post that to find the apache user I can run the following command:

ps aux | egrep '(apache|httpd)'

Wich outputs the following:

135   root     /usr/bin/httpd -k start
138   daemon   /usr/bin/httpd -k start
139   daemon   /usr/bin/httpd -k start
140   daemon   /usr/bin/httpd -k start
1133  root     egrep (apache|http)
  • Related: How to set permissions in /sys/ permanenty – Mark Plotnick Dec 27 '17 at 23:19
  • @MarkPlotnick, thanks for answering but I saw that thread before but I can't see how it can help me. First of all what is the "ALL ALL = (ALL) NOPASSWD...." given in the solution is it a shell command? Because my system always gives a syntax error unexpected "(" and if I remove the parentheses it says "ALL: not found". In that thread it's also suggested to use a service in the systemd directory, the problem is that my system doesn't has a systemd directory. – Hello World Dec 28 '17 at 9:22
  • "ALL ALL = (ALL) NOPASSWD...." is an entry in the sudo config file. sudo is a program that lets you configure things so that sudo command, when run by an ordinary user, runs command as root. This question has more details; allowing writes to /sys by ordinary users is a common question. An init script would be easier, except that you said you'll need to chmod the files and directories at arbitrary times after booting. – Mark Plotnick Dec 28 '17 at 11:05
  • @MarkPlotnick but I don't have a sudo config file because this a very simple build and the only user is root. And even if I manage to insert that entry somewhere that will make it work, will this entry allow apache to read and write these files using fread and fwrite in php? And if I export the pins will the new directories and files writable and readable by the apache? – Hello World Dec 28 '17 at 11:11
  • From what I've read, if you cause the kernel to create new files and directories under /sys, there's no way to have the kernel automatically give them alternative owners or modes (unless they trigger an event that udev handles, but you might not have that); you'll need to run more chmod or chown commands. Hopefully someone familiar with your specific type of small system can offer a convenient way to do what you want. – Mark Plotnick Dec 28 '17 at 12:27

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