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Raspberry Pi and /dev/mem access

Former Member

Question(s) regarding Raspberry Pi and GPIO.

 

Been working with RPi.GPIO for several weeks trying to get the following script to run: (from Third Eye Visions, using the GPIO Python library that they suggest to use)

 

import RPi.GPIO as GPIO

GPIO.setmode (GPIO,BOARD)

GPIO.setup (7, GPIO.OUT)

GPIO.output (7, True)

 

When running from the Lynux command line, an error is posted “no access to /dev/mem.  Try running as root”

 

I go to command line and run sudo/home/pi/file name and another error is returned “command not found”.

 

Doing a brief search on line, I don’t seem to be the only person having this problem.  I simply don’t understand the solutions that are presented and it is not clear that the solutions solve the problem.

 

When using RPi.GPIO 0.5.4 revision of the Python Package Index, isn’t this problem resolved?

 

I am using the Debian Wheezy Rasbiabn 2012.12.img 192, Debian GNU/Linux 7 raspberry pi tty1

 

I have Python 2.7, 3.2 and 3 on the SD and Python IDE.

 

I want to program the raspberry pi using GPIO functions with Python not C or any other script.

 

Why won’t the current upgrade of Raspberry Pi from Third Eye Visions work with the above script?  This is not the only GPIO program (from other sources) that I have tried and receive the same result.  I can control the pins in the command line of Linux from the keyboard using set mode, etc and read the status of the pins using readall.

 

I have used Pygame with this distribution of Debian and it works perfectly.

 

Can anyone supply a simple fix for this problem?  Can it be solved with a new SD loaded with a raspberry pi compatible program set-up with Python?  If so. where can I find one.? Or can I simply add one or two lines to the script that will allow access into

/dev/mem and then reinstate root privileges to /dev/mem at the point of exit from the program?

 

Help!

morgsterdad

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    Bill,

    A Linux system has some protections: "normal" users cannot access things that could damage possible other users on the system or the system itself. A command "delete-all-files" would also delete the operating system, but protections are in place that should prevent this.

     

    Now, when you try to access the GPIO pins, the way that "import RPi.GPIO as GPIO" works is that it accesses  the hardware of the CPU directly. This is something that the operating system cannot allow to normal users. So... if you're logged in as "pi" the system will not allow you access to the hardware in "/dev/mem". The system tells the program "permission denied", the program catches this error and prints a message that explains what you can do (run as root).

     

    Now, when you DO run it as root, you seem to be getting a different problem. somehow, a file is not being found.

     

    Again a simple problem if you know how to solve it. But things like "switch to a different operating system" will not automagically solve these problems. All Linux operation systems will protect the hardware by preventing access to "/dev/mem" for normal users. All Linux systems will report an error if you mistype a command.

     

    If you ask us to spot-the-typo in your commands and then make typo's in the post about it, that makes things a lot harder to help you in "one go".

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  • 0

    Bill,

    A Linux system has some protections: "normal" users cannot access things that could damage possible other users on the system or the system itself. A command "delete-all-files" would also delete the operating system, but protections are in place that should prevent this.

     

    Now, when you try to access the GPIO pins, the way that "import RPi.GPIO as GPIO" works is that it accesses  the hardware of the CPU directly. This is something that the operating system cannot allow to normal users. So... if you're logged in as "pi" the system will not allow you access to the hardware in "/dev/mem". The system tells the program "permission denied", the program catches this error and prints a message that explains what you can do (run as root).

     

    Now, when you DO run it as root, you seem to be getting a different problem. somehow, a file is not being found.

     

    Again a simple problem if you know how to solve it. But things like "switch to a different operating system" will not automagically solve these problems. All Linux operation systems will protect the hardware by preventing access to "/dev/mem" for normal users. All Linux systems will report an error if you mistype a command.

     

    If you ask us to spot-the-typo in your commands and then make typo's in the post about it, that makes things a lot harder to help you in "one go".

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