Help with crontab and py script

[some_evil]

Hi guys,

I am trying to automate my first script on my py to run at a specific time, and in my attached example it is trying to run at 8.37pm every day of the year, but the output file of my python script seems to be empty after its scheduled start time.

2015-03-11 21_18_35-BVK - RaspberryPi - WinSCP.jpg (23.41 KiB) Viewed 797 times

I can manually start this script by typing:

Code: Select all

sudo python /BVK/ds18.py

When i run the code it outputs the temperature to a text file, but its not producing anything, and im unsure how to look for errors.... any tips on what I can do to find my problem?

Thanks

[RaTTuS]

1) dont use sudo in cron
if you need to run it as root use the roots cronttab
i.e.
sudo contab -e
2) always use full paths to everything
.... /full/path/to/command/processor /full/path/to/script
or
... /full/path/to/script
as you will have
#!/full/path/to/processor
in the first line of your script anyway
and the output
as you are not showing on the command line this must be in your script
again have the full path to the output file in there
and I would use a RAM disk location i.e.
/tmp
3) cron will report errors to the syslog
i.e.
grep CRON /var/log/syslog

[some_evil]

1) dont use sudo in cron
if you need to run it as root use the roots cronttab
i.e.
sudo contrab -e

So i should edit it to look like...
37 20 * * * python /BVK/ds18.py ???

Also I am a n00b, but i assume you meant 'sudo crontab -e' ???

2) always use full paths to everything
.... /full/path/to/command/processor /full/path/to/script
or
... /full/path/to/script
as you will have
#!/full/path/to/processor
in the first line of your script anyway

ok this is good, I have seen this line in scripts from time to time but never knew what it did or how to apply it. Is the "#!/full/path/to/processor" going to be the same for eveyone on a Pi? I dont quite get what this is doing?

I have never used this first line before, but my basic scripts have run (up until this one).

as you are not showing on the command line this must be in your script
again have the full path to the output file in there

this is the one thing I was able to check without further clarification, i went through my script and realized that I had only put output = 'outputFile.txt', i just changed it to output = '/BVK/outputFile.txt' and it has just run successfully and automatically.

and I would use a RAM disk location i.e.
/tmp

What would you use this for??


Thanks for your help!

[RaTTuS]

Also I am a n00b, but i assume you meant 'sudo crontab -e' ???

yes and I've edited the original post

ok this is good, I have seen this line in scripts from time to time but never knew what it did or how to apply it. Is the "#!/full/path/to/processor" going to be the same for eveyone on a Pi? I dont quite get what this is doing?

yes in general -
if people have installed via apt-get then they all should be in the same place, though if it fails you'll get an error

well as you have not posted your script I cannot comment on it as to where you store things

but if you type
mount
then if it shows
something similar to
tmpfs on /tmp type tempfs ( ....)
then that device is a ramdisk
this will save on writes to the SD card [though once a day is nothing] but it also means that it will be cleared on reboots so do don't have random stuff left on the Sdcard

[Joe Schmoe]

Two things (related):

1. Check in your syslog, searching for the string "mta" (in any case, not sure which spelling [case] it is in there with). You should see a message like (paraphrasing) "MTA not configured". This message is telling you that your cron job generated something on standard output and/or standard error, and the cron system tried to email that output to you, but couldn't, because you haven't setup your MTA (mail transfer agent).
2. Fix the above problem, so that the cron system can send you the output of your command; once you do this, it should be obvious what the problem is and thus easy to fix it. There are two ways of fixing the MTA problem - an easy way and a hard way:
   1. Easy way: add a line like: MAILTO=you@yourprovider.com
   2. Hard way: Install/configure/debug something like sendmail/postfix/exim
   If you follow the first method, then whatever output the cron job generates will be mailed to your outside email account (yahoo, gmail, whatever).

Note finally that you can, in theory sort of, solve this problem by doing the usual "exec 2>&1 >> /tmp/logfile.log" hack, but it is better, at this stage of the game, to let the cron system do its thing in emailing you.