Can't run python script from cron

Question

Running latest version of Rasbian and want to execute /home/pi/temp.py from cron every 2 min. Have chmod 755 on the file

When I run the command from the prompt it executes fine and the script does what it supposed to: pi@raspberrypi ~ $ python temp.py

I have added it in cron like: */2 * * * * /usr/bin/python /home/pi/temp.py

I never get any output from the script. I have other scripts the run fine from cron. What do I miss?

This is what temp.py looks like

!/usr/bin/python import time # Create a unique timestamp for inclusion in the log... timestamp = time.strftime("Time: %H:%M, Date: %Y%m%d, ") # append the filename with the date (this will start a new log daily)... logname = time.strftime("") filename = "".join(["/home/pi/bredhult_temp.txt"]) # If already created, this will open the current log file, if not it will create a new on datafile = open(filename, "a") # open the sensor log file as seen in the tutuorial (replacing 28-000003f1cede with the n tfile = open("/sys/bus/w1/devices/28-000006879f89/w1_slave") # read the data and close the file... text = tfile.read() tfile.close() # Split the data and extract the temperature value... temperature_data = text.split()[-1] temperature = float(temperature_data[2:]) temperature = temperature / 1000 # write our newly formatted date, time and sensor value to our log file... datafile.write(timestamp + "Temp: " + str(temperature) + "\n") datafile.close() 

Answer 1

SUGGESTION:

First create a simple Python script - that just outputs something to a file.

with open("/tmp/hello.txt", "w") as outfile: outfile.write("hello") 

You don't need the hashbang (#!/usr/bin/python) here (although there is no harm in adding it if you want) : since you will be using the Python executable to call a script in your cron.

To simplify the cron (and you need to decide whether to use 'root' or 'pi' (or another) crontab here) : I assume you will be using the 'root' cron here - use the @reboot instead of a specific time.

$ sudo crontab -e 

Make the change, and save the crontab:

@reboot /usr/bin/python /home/pi/simple.py $ sudo reboot 

Now check that /tmp contains the 'hello.txt' file after the reboot. If this works: swap out the (crontab -e again) this simple script for your existing one , reboot ) - does this work ?

Note: you can also check your system logs for evidence that the cron is running your script or not:

See this other post for information.

Answer 2

Looking at your pasted example, the shebang is missing #; your first line should be:

#!/usr/bin/python 

Once that is fixed I would try to make your python script executable with the following line:

chmod +x /home/pi/temp.py 

And then simply call it with the following in your crontab:

*/2 * * * * /home/pi/temp.py 

Answer 3

This is how I run a python program as root every five minutes.

johnma@raspberrypi ~ $ sudo crontab -l # # For more information see the manual pages of crontab(5) and cron(8) # # m h dom mon dow command */5 * * * * /home/johnma/do-DHT-once 

Here is the source of do-DHT-once which automatically outputs sysout and syserr to temp files in /tmp and checks to see if a previous copy of the script is still running and tries to kill it if it is. The python program outputs its PID to file /tmp/DHT.pid. The script can also be disabled by creating a file called DHT.disabled in $DIR:

#!/bin/bash # Set home directory where script exists DIR=/home/johnma if [ -f $DIR/DHT.disabled ] then exit 1 fi if [ -f /tmp/DHT.pid ] then echo Attempting to kill process `cat /tmp/DHT.pid` >>/tmp/DHT.log 2>>/tmp/DHT.err.log kill -HUP `cat /tmp/DHT.pid` >>/tmp/DHT.log 2>>/tmp/DHT.err.log fi # change to home directory cd $DIR # run the program using the debug version of python python2.7-dbg $DIR/DHT_googledocs.twitter.once.py >>/tmp/DHT.log 2>>/tmp/DHT.err.log if [ -f /tmp/DHT.pid ] then echo Attempting to delete /tmp/DHT.pid >>/tmp/DHT.log 2>>/tmp/DHT.err.log rm /tmp/DHT.pid >>/tmp/DHT.log 2>>/tmp/DHT.err.log fi 

Finally, the file do-DHT-once has permissions 755 to allow it to be executed:

johnma@raspberrypi ~ $ ls -l do-DHT-once -rwxr--r-- 1 johnma johnma 703 May 12 2014 do-DHT-once 

Answer 4

I had problems with Python script as cronjob as well. I recommend to write a simple wrapper bash script which sets PYTHONPATH (or whatever) correctly, put it in $HOME/bin and run a script like the following example:

#!/bin/bash # Optionally set PYTHONPATH export PYTHONPATH=/path/to/python/libraries:$PYTHONPATH # Run your script with your preferred Python installation # in case you have more than one /path/to/your/python /path/to/yourscript.py