1

I got a Raspberry PI and, even with the root user, I got some "permission denied" using commands like when I want to access the gpio. I tried with and without sudo. sample :

# cd /sys/class/gpio/

# ls

# sudo echo 24 > export (Permission denied)

But I can create users and add them to the sudo list. I don't understand, how can it be possible ?

Thanks to answer me.

  • "sudo echo" won't work, because "echo" is internal bash command and not a program or an executable script. – lenik Oct 1 '13 at 23:44
  • @lenik : Incorrect! Sort of. echo is a built-in, but there's also an executable (try whereis echo). However, /bin/echo foo > bar still won't work. The problem is the output redirection (>) which is done by your current non-sudo shell, to a file you don't have permissions on. – goldilocks Oct 2 '13 at 9:15
3

As lenik sayed, echo is a built-in and thus cannot be used with sudo like that.

But in your case, it's the redirection (>) which cause problem (thanks goldilocks). Indeed, the redirection is also made by the shell and thus have the same restriction than the built-ins.

Instead, you should switch to root first:

$ sudo su
# echo 24 > export

Or if you don't want to switch:

$ sudo su -c 'echo 24 > export'

Or, only for writing in a file:

$ echo 24 | sudo dd of=/sys/class/gpio

You can have a list of shell built-ins with the following command:

$ man builtins
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    +1 Except lenik is sort-of wrong (see my comment to the OP). There are some other ways around the problem, e.g. echo 24 | sudo dd of=/sys/class/gpio. – goldilocks Oct 2 '13 at 9:16
  • Thanks for the clarification. I indeed didn't think about the redirection. – Gagaro Oct 2 '13 at 9:31

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