Executing a python script including GPIO commands by cron in Raspberry Pi 2

Environment

• Raspberry Pi 2
• raspbian-jessie-lite
• Windows 8.1
• PuTTY 0.66 (SSH)

Issue

Can’t get cron to execute a python script with sudo. The script deals with GPIO input so it should be called with sudo. The program is supposed to save temperature and humidity to files but cat temp.txt and cat humid.txt gave me empty strings.

crontab

sudo crontab -e

* * * * * python /home/dixhom/Adafruit_Python_DHT/examples/temphumid.py 1>>/tmp/cronoutput.log 2>>/tmp/cronerror.log

python script

#!/usr/bin/python

import sys
import Adafruit_DHT
import datetime

# Adafruit_DHT.DHT22 : device name
# 4 : pin number
humidity, temperature = Adafruit_DHT.read_retry(Adafruit_DHT.DHT22, 4)


if humidity is not None:
        f = open("humid.txt","w")
        str = '{0}, {1}'.format(datetime.datetime.now().strftime("%Y/%m/%d %H:%M:%S"), humidity)
        f.write(str)

else:
        print 'Failed to get reading. Try again!'
        sys.exit(1)

if temperature is not None:
        f = open("temp.txt","w")
        str = '{0}, {1}'.format(datetime.datetime.now().strftime("%Y/%m/%d %H:%M:%S"), temperature)
        f.write(str)
else:
        print 'Failed to get reading. Try again!'
        sys.exit(1)

cronerror.log and cronoutput.log

(empty)

What I tried

• sudo crontab -e
• /usr/bin/python in cron
• chkconfig cron (cron on)
• sudo apt-get update sudo apt-get upgrade
• sudo reboot

Any help would be appreciated. Thanks.

Answer

Option 1: You can edit /etc/crontab. There you can specify which user shall execute the respective job in a column right after the schedule.

Option 2: Edit the crontab of root using

sudo su
crontab -e

I would go for the second option because this is what the docs suggest…

(Disclaimer: No warranties taken regarding the GPIO stuff. I just assume you are right with the “needs sudo”, because I never do GPIO on the raspi. So I referred to running a script as root only.)