Using cron to start a python script at every boot

Question

I tried using cron to start python script , at boot (as mentioned in the link).Running a python script At Boot using cron

I made a python script "hello.py":

#!usr/bin/env python 
import time
print "Hello World!"
time.sleep(10)

Then chmod +x hello.py. I checked,if it running or not,it is giving me output. I used crontab -e command and added the line @reboot python /home/pi/hello.py &. Reboot using sudo reboot , but nothing happened! I am newbie .Although I read many discussions but I am not able to fix that!

how are you checking if your hello.py ran? because you won't see the printed "Hello World!". Try writing your "Hello World!" to a file and check if it's in the file ;-) — cptPH
– cptPH, Commented Dec 3, 2013 at 14:30
@Patrick I mean that if I ran that program on terminal using python hello.py it is running! and giving me output. — Maham
– Maham, Commented Dec 3, 2013 at 14:34
well the next thing i see is that the shebang is wrong: it is missing a / after !. other than that it's not really clear to me what you want :O — cptPH
– cptPH, Commented Dec 3, 2013 at 14:36
@Patrick is right, the problem seems like that you don't know the difference between foreground process and background process. In your case, running "python hello.py" in terminal is running a foreground process, and you can see the output directly from terminal. The cron version is a background process, the output can not be seen directly(that's why it is "background"), you can modify(crontab -e) your job as: python hello.py > /tmp/result.txt, the output will be "redirect" to /tmp/result.txt, and it'll prove that your script ran. — waterlee23
– waterlee23, Commented Dec 3, 2013 at 14:43

Paul · Accepted Answer · 2013-12-03 14:39:02Z

1

Generally when I want to verify whether a cronjob ran or not, I redirect all output to a log file like so:

12 0 * * * python /Path/To/File.py  > /Path/ToLog/log 2>&1

Then you can check this log timestamp and for its contents

answered Dec 3, 2013 at 14:39

Paul

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2 Comments

Maham Over a year ago

Yes! as @wentao explained, I verified this! :)

Paul Over a year ago

Ahh I hadn't seen @wentao 's explanation. It is spot on. Notice that I also redirect stderr with the 2>&1 This will put all stderr and stdout into the same file, which might or might not be what you want

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