I'm new to RPI and to Python 3 and I have a problem running this code on a RPI 2.

import RPi.GPIO as GPIO
import time
redled = 4
greenled = 26
GPIO.setup(redled, GPIO.OUT)
GPIO.setup(greenled, GPIO.OUT)
count = 1
while count < 100000:
    GPIO.output(redled, 1)
    GPIO.output(greenled, 1)
    GPIO.output(redled, 0)
    GPIO.output(greenled, 0)
    count = count + 1


I get this error.

Traceback (most recent call last): File "/home/pi/testreactionrepeat.py", line 7, in GPIO.setup(redled, GPIO.OUT) RuntimeError: No access to /dev/mem. Try running as root!

I was using this code with no problems a couple of days ago and can't figure out what I'm doing wrong now. I found a similar problem and the answer was to run "sudo su" but I get a syntax error when I try that.

  • Please edit your question and add the specific error sudo su is returning. Commented Aug 20, 2015 at 23:32

1 Answer 1


Let's assume that your program is called


Open terminal and type

sudo python program.py 

This will run your python program as root giving it the necessary permissions to access/modify the GPIO pins.

  • I get this when I type sudo python reactionrepeat.py into terminal. Traceback (most recent call last): File "reactionrepeat.py", line 3, in <module> GPIO.setmode(GPIO.BCM) AttributeError: 'module' object has no attribute 'setmode' Commented Aug 21, 2015 at 11:07
  • can you run "sudo apt-get update && sudo apt-get upgrade" in terminal, this will update your system with the latest software and hopefully with the latest RPi.GPIO modules and thuis fix this issue. Commented Aug 21, 2015 at 11:33
  • I did the update/upgrade, and it appeared to go well. However, my code still won't run, even though it ran just fine a couple of days before I had the problem. I still get the same messages as before when I run the program and when I type in sudo python reactionrepeat.py. Could this be a hardware problem? Commented Aug 21, 2015 at 21:53
  • @nashville_bill no this is definitely a software problem. Are you on the latest raspbian OS? Commented Aug 22, 2015 at 3:22
  • I'm getting this experience with Ubuntu Mate 15.10 when trying to use dot3k.
    – user43492
    Commented Mar 20, 2016 at 17:10

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