Executing a Python program from crontab

Question

I have created a Python 2.7.3 program on my Raspberry Pi that writes an XML file. When I run this program using IDLE's F5 key, it runs and outputs the XML file. When I run the same program using an LXDE terminal at the pi@raspberry-pi ~ $ prompt by typing python program_name.py, it also works as intended and outputs the XML file.

Now I want to refresh the XML file every 15 minutes, and it sounds like I should be able to do this using crontab.

So I started with the command crontab -e which opens up the editor (nano, in my case). I entered as the last line the following:

*/15**** python /home/pi/program_name.py

I also tried various variants as follows:

*/15**** sudo python /home/pi/program_name.py

and:

*/15**** python program_name.py

When I exit the program I get the error message:

"/tmp/crontab.nyQZsu/crontab":23: bad command
errors in crontab file, can't install.

Any ideas on what I am doing wrong?

Kevin J. Chase · Accepted Answer · 2016-03-29 06:00:03Z

3

The hour, minute, month, and other fields in a crontab file are whitespace-separated. Unless you've got a cron variant I haven't seen before, cramming all your fields together into a single blob like "****" is a syntax error.

From the POSIX Programmer's Manual:

[...] a crontab entry is a text file consisting of lines of six fields each. The fields shall be separated by <blank>s.

That's what the "bad command errors in crontab file" message is telling you: The file you fed crontab is invalid, so the program refuses to "install" (accept) it.

For comparison, here's the error I got when trying to install a file that included a deliberately bogus line, ***** /bin/echo:

$ crontab -e
crontab: installing new crontab
"/tmp/crontab.XXXXe2lUUa":5: bad hour
errors in crontab file, can't install.
Do you want to retry the same edit? n
crontab: edits left in /tmp/crontab.XXXXe2lUUa
$

edited Mar 29, 2016 at 6:00

answered Mar 29, 2016 at 5:50

Kevin J. Chase

3,9764 gold badges25 silver badges43 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Gary Over a year ago

Thank you. That works. From any of the examples I saw, I did not pick up on the fact that each of the 6 fields were separated by a blank space. (just realized that I'm not supposed to say "thanks" in these comments!!)

aroy · Accepted Answer · 2016-03-29 04:27:24Z

-1

Try to use 15 instead of /15

Also, if you want a crontab entry to run as root, it's better to put it in a /etc/cron.d/ file than in root's own user-level crontab.

answered Mar 29, 2016 at 4:27

aroy

4823 silver badges11 bronze badges

2 Comments

Gary Over a year ago

What is the benefit of having the crontab entry to run a root?

Kevin J. Chase Over a year ago

A lone 15 in the minutes column would run the script at 15 minutes past each hour, not every 15 minutes.

Collectives™ on Stack Overflow

Executing a Python program from crontab

2 Answers 2

1 Comment

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related