What is wrong with my cron job?

Question

I'm new to linux, and was told I could use a feature called cron job to run a python script I made execute every 10 minutes. Problem is the the python script isn't running. There doesn't seem to be a clear cut way to know if I've formatted the job correctly, but in any case I've tried a number of paths to no avail.

Because I'm so new I'll show you the steps I took. On my RasPi, I first typed "crontab -e" and get a field like this:

# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task

Skipping more help text

# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/

# m h  dom mon dow   command

and I add my line at the bottom, without removing the text above.

*/10 * * * * ~/WeatherProject/HOURLY/windDirExtract.py

The above didn't work, and someone else did something similar to this but still no luck.

*/10 * * * * /home/MyName/WeatherProject/HOURLY/windDirExtract.py

and then I tried different permutations but I've got nothing.

*/10 * * * * /home/MyName/WeatherProject/HOURLY python windDirExtract.py
*/10 * * * * /home/MyName/WeatherProject/HOURLY windDirExtract.py

I'll make any edits if I haven't been clear, but first big question is can I even run short little python scripts with Cron Job, or did I just get bad advice?

Solution 1

Make sure your command works from the command line first

/usr/bin/python /home/MyName/WeatherProject/HOURLY/windDirExtract.py

Then try the same in the crontab

*/10 * * * * /usr/bin/python /home/MyName/WeatherProject/HOURLY/windDirExtract.py

Solution 2

Your script seems to work fine, running this from cron though will not work as expected. For example:

$ ./windDirExtract.py 

START
2013-09-23 22:32:39.376584
283

Running this script produces the output above. But with cron the output needs to go somewhere. I would suggest writing it out to a file to start, like so via cron:

*/10 * * * * /home/MyName/WeatherProject/HOURLY/windDirExtract.py >> /home/MyName/weather.log

This will capture the output to the log file, weather.log where you can review it to see if the cron is running correctly. Doing the above will continuously append the output every 10 minutes from your script to the log file like this:

START
2013-09-23 22:32:39.376584
283
START
2013-09-23 22:42:39.376584
283
...

Comments

[phemmer]

Is your script marked executable (chmod +x), and does it begin with #!/usr/bin/python?

[slm]

Check the logs, Redhat:sudo grep CRON /var/log/messages or Debian/Ubuntu: sudo grep CRON /var/log/syslog

[Monte Carlo]

If my understanding of what a distro is happens to be correct, I'm running Raspbian.

[slm]

Do a ps -eaf|grep cron do you get any processes running?

[Monte Carlo]

slm for sudo grep CRON I get a log Sep 24 01:30:01 raspberrypi /USR/SBIN/CRON[13386]: (Oscar) CMD (~/WeatherProject/HOURLY/windDirExtract.py) Sep 24 01:30:01 raspberrypi /USR/SBIN/CRON[13385]: (CRON) info (No MTA installed, discarding output)

[Monte Carlo]

Meanwhile ps -eaf|grep cron gives me this output root 1953 1 0 Sep06 ? 00:00:06 /usr/sbin/cron Bob 13422 13219 0 01:37 pts/0 00:00:00 grep --color=auto cron

[slm]

OK, good so you have cron and it's running. The MTA is mail transfer agent, cron tries to send an email with the results of what ran in it, this says it wasn't able to do that.

[slm]

Perfect so we have a functioning cron, that's 1/2 the battle.

[slm]

Your script is likely not running for something in the script itself then. Can you share that? You can use pastebin.com to share large files. Post link here.

[slm]

When ready please prefix the comment with @slm - so I know you've replied to me, otherwise I will lose sight of your Q, I'm bouncing to other ones as well.

[slm]

See my answer, let me know if that helps?