Cron job to run a python script every 1 minute

Question

I know this question has been answered many time. I refereed heemayls answer in this post to set up the cron job. However, it is not working. Any idea on what is going wrong?

*/1 * * * * /usr/bin/env python3 /home/me/DownloadImages1.0.py

The following is the output of crontab -l

# 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
# 
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').# 
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
# 
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
# 
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
# 
# For more information see the manual pages of crontab(5) and cron(8)
# 
# m h  dom mon dow   command
*/1 * * * * /usr/bin/env python3 /home/me/DownloadImages1.0.py

Answer 1

You need to tell your script which display you wish the script to run, otherwise it won't run.

Use a command like this:

*/1 * * * * DISPLAY=:0.0 /usr/bin/env python3 /home/me/DownloadImages1.0.py

You can also use a global DISPLAY variable just placing this at the top of your cronjobs list

# m h  dom mon dow   command
DISPLAY=:0.0
*/1 * * * * /usr/bin/env python3 /home/me/DownloadImages1.0.py

And you can also invoke the DISPLAY by exporting the variable from a bash script via

#!/bin/bash
export DISPLAY=":0.0"
/usr/bin/env python3 /home/me/DownloadImages1.0.py

Answer 2

Nothing was working for me as well, because whatever I was doing, or the cron job you have written above is correct.

*/1 * * * * /usr/bin/env python3 /home/me/DownloadImages1.0.py

The problem was something else in my case which I never imagined, as when I execute the same python script on terminal, it would run fine.

python3 /home/me/DownloadImages1.0.py

Until I read somewhere that, the crontab version, runs as, when we run command via sudo su

When I ran, python3 /home/me/DownloadImages1.0.py in sudo su, it started giving me library not installed errors. After I did pip3 install xxx libraries install inside sudo su itself, the command ran successfully.

After that, crontab ran successfully as well.

In short try following out -

1- create hello.py

print('hello')

2- write a cron job to execute above python script and output to some log file, to verify whether your crontab is actually working without any python dependency.

sudo touch /home/me/out.txt
sudo crontab -e
1 (put next minute here) * * * * /usr/bin/env python3 /home/me/DownloadImages1.0.py > /home/me/out.txt

3- Check the logs of crontab

tail -f /var/log/syslog | grep cron -i

After your hello.py script is executed, check the out.txt file. If it has contents then everything is fine (this answer is only valid if there is output in out.txt).

4- sudo su 5- make following command run successfully.

tail -f /var/log/syslog | grep cron -i

6- Now, your cron job */1 * * * * /usr/bin/env python3 /home/me/DownloadImages1.0.py should run successfully.