如何在LINUX上使用cron运行python脚本

Question

I'm trying to run a python script on my raspberrypi using cron .

I did the following:

crontab -e # To edit a crontab job

After the cron file opened, I added the following line:

@reboot /usr/bin/python /home/pi/path/to/file/example.py > /home/pi/cronlogs/mylog.log # JOB_ID_!

If I understand the documentation correctly, this cron job should be executed every time after the system booted up. However in my case, when I reboot the computer, the script will not be executed.

What's strange:

• I checked the log file and it's empty, so it seems like everything goes fine
• If I run the given command manually (so basically write the following code to the terminal) it executes and works correctly: /usr/bin/python /home/pi/path/to/file/example.py > /home/pi/cronlogs/mylog.log

I guess I missed something really obvious but I can't see it. Please can I ask for any advise how to debug this. Thanks!

Answer 1

The cron definition looks correct; I just checked this on my Pi running Debian stretch and it works OK:

@reboot /usr/bin/python /home/pi/example.py > /home/pi/mylog.log

Some other possible reasons it might not work:

• working directory issue (if you're using relative paths)
• a long running script (being a scraping script it might take a while to complete) - you can check if it's still running using ps aux | grep python ps aux | grep python
• the script does not output anything (would need some more details about the script)

Just to be sure you catch any errors from the script, redirect stderr to stdout by using 2>&1