Cron, python and saving to a file
I’ve got a veeery simple script written in python that tests my internet connection na saves parsed data to a json file:
#!/usr/bin/python3
import subprocess, json, os
from datetime import datetime
# run the bash script and parse results
def speedtest():
result = subprocess.run(["/bin/speedtest-cli", "--simple"], stdout=subprocess.PIPE, encoding="UTF-8").stdout
# result = os.system("speedtest-cli --simple")
download_str = result.find("Download: ") + 10
download_speed = result[download_str:result.find(" Mbit/s", download_str)]
upload_str = result.find("Upload: ") + 8
upload_speed = result[upload_str:result.find(" Mbit/s", upload_str)]
ping_str = result.find("Ping: ") + 6
ping = result[ping_str:result.find(" ms", ping_str)]
return download_speed, upload_speed, ping
def save_to_json(data):
# load existing data to a dict
existing_data = []
with open("/home/trendkiller/development/python/py_speedtest/data.json") as fp:
existing_data = json.load(fp)
payload = {
"date": datetime.now().strftime("%d/%m/%Y"),
"time": datetime.now().strftime("%H:%M"),
"download": data[0] + " Mbps",
"upload": data[1] + " Mbps",
"ping": data[2] + " ms"
}
existing_data.append(payload)
# save to a json file
with open("/home/trendkiller/development/python/py_speedtest/data.json", "w") as f:
json.dump(existing_data, f, indent=4)
def main():
test_result = speedtest()
# save to a json_file
save_to_json(test_result)
return 0
if __name__ == "__main__":
main()
It runs smoothly when I call it from terminal.
I would like to automate it so it can test my connection hourly.
For this I’m trying to use CRON and it works when I schedule it to run every minute (data is saved to data.json).
But when I try to run it hourly, data isn’t passed to a json file.
Here’s my crontab file:
@hourly /bin/python3 /home/trendkiller/python/py_speedtest/main.py
While looking at the grep "CRON" /var/log/syslog
there’s nothing strange (to my knowledge):
Feb 5 08:00:01 home-lab CRON[119326]: (trendkiller) CMD (/bin/python3 /home/trendkiller/development/python/py_speedtest/main.py > /home/trendkiller/development/python/py_speedtest/log.txt)
Feb 5 08:00:04 home-lab CRON[119325]: (CRON) info (No MTA installed, discarding output)
Feb 5 08:17:01 home-lab CRON[119719]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Feb 5 09:00:01 home-lab CRON[120590]: (trendkiller) CMD (/bin/python3 /home/trendkiller/development/python/py_speedtest/main.py > /home/trendkiller/development/python/py_speedtest/log.txt)
Feb 5 09:00:02 home-lab CRON[120589]: (CRON) info (No MTA installed, discarding output)
Feb 5 09:17:01 home-lab CRON[120798]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Any help would be very useful,
thanks in advance (and don’t mind the clutterred code :P).
A quick answer:
Write a script in /etc/cron.hourly
.
runpy
script:
#!/bin/bash
/bin/python3 /home/trendkiller/python/py_speedtest/main.py
Then make it executable:
sudo chmod +x /etc/cron.hourly/runpy
Test with --report
or --test
:
run-parts --report /etc/cron.hourly
First of all, make the program executable (chmod u+x /home/trendkiller/python/py_speedtest/main.py
) and ensure it has a valid Python interpreter as its first line. The cron command would suggest #!/bin/python3
but you’ve written #!/usr/bin/python3
. Which is correct?
The CRON log output also suggests that the command you’ve shown us isn’t actually the command you’re running (one has a redirection of stdout to a log file, the other does not). Both are missing redirection of stderr.
You can either capture the output in the system logger:
-
Capture the output from your program, including errors written to stderr:
@hourly /home/trendkiller/python/py_speedtest/main.py 2>&1 | logger -t py_speedtest -p user.info
-
Read the logfile (probably
grep py_speedtest /var/log/user.log
)
Or if you’re not running a syslogger such as rsyslog
you may prefer to just write the output to a file. But remember to truncate the file every so often, or replace it (use >
instead of >>
) each time your program runs rather than append to it.
-
Capture the output from your program, including errors written to stderr:
@hourly ( date; /home/trendkiller/python/py_speedtest/main.py )>"$HOME/.py_speedtest.log" 2>&1
-
Read the logfile (for example
less "$HOME/.py_speedtest.log"
)
I would think it most likely that you’re not in the directory you think you’re in. If this is the case you can fix it by changing to your $HOME
directory. For example,
@hourly cd && ( date; /home/trendkiller/python/py_speedtest/main.py )>".py_speedtest.log" 2>&1
(If your home directory is /home/trendkiller
you can remove that from the command too: python/py_speedtest/main.py
)