Problem with crontab

[hmojal]

Hi all,

I have a script which takes a picture with the raspberry cam and then upload it to a dropbox.
The script is running succesfully when i just tip

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./testcam.sh

The thing is I need this script to run every 2 minutes.
So I looked and find that linux as the crontab function which is made for that.
I tip "sudo crontab -e" and updated this file this way :

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# Edit this file to introduce tasks to be run by cron.
*/2 * * * * pi /home/pi/testcam.sh
#
# 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

and so on..

And... nothing happen every two minutes....
On the link of the dropbox uploader script (https://github.com/andreafabrizi/Dropbox-Uploader) there are things sayed about the use with a cron job but I don't get it..

Any one for a big help ?

Thank's !

Hugo

[Joe Schmoe]

The thing is I need this script to run every 2 minutes.
So I looked and find that linux has the crontab function which isn't made for that.

Here we go again.

Read my comments in the other "crontab" thread.

[hmojal]

You posts telling not to use crontab ?

[DirkS]

Here we go again.

Read my comments in the other "crontab" thread.

You meant this one http://www.raspberrypi.org/forums/viewt ... 08#p602708 where you say

This thread bears out well my constant assertion that cron is complex and weird and not the right tool for most things on the Pi. The fact that "mail" doesn't work (even locally) is a joke and renders most cron debugging jobs into the "what should be a 5 minute debugging job becomes a 6 month one" category. (Credit marty@winbatch.com for this last nice turn of phrase…)

It is especially not the right tool for running something "every minute", for reasons I've detailed at length in other posts - there are clearly better ways to "run something every minute".

So we have to look somewhere else again (after googling for it?) what these better ways, according to you, are?

[tberry]

I have precisely the same problem as the OP and saw Joe Schmoe's comments in the thread linked earlier. I searched for his comments on how to run a script every minute without using a cron job but could not find them. @Joe Schmoe, could you link me to them , please?

As I mentioned, I have the exact same problem. I am taking a picture from a webcam every minute. I need to ftp it to a server every minute. I have written a very simple script using wput which does this when I run ./simple.sh in the terminal. It will not run when I try to schedule it as a cron job, even though the system log shows that is is running each minute. It simply fails to run.

I don't want to hijack this thread with my details but let's just say I've tried a LOT of things including using cron.d. I suspect my solution is the same as the OP's and if Joe Schmoe has suggestions that work, I'm all ears.

[tberry]

I may have an answer and a solution. I Googled why it was a bad idea to run a cron job every minute and it appears that if your job doesn't finish in the one minute you allow, it will run the job again on top of itself. Cron apparently does not keep this from happening.

Suggested solutions were to simply code an infinite loop script with the command, tell it to sleep a few seconds after running, then loop. I am using wput to upload the image webcam.jpg from a folder on the desktop called webcam via ftp and will try a script that looks like this:

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#!/bin/bash
while true
do
wput --binary --user=your_ftp_username --password='your_ftp_password' ftp://ftp.your_ftp_location_.com /home/pi/Desktop/webcam/webcam.jpg
sleep 60
done

To ensure this file runs on reboot (say, from a power outage), follow the instructions here: http://www.raspberrypi.org/documentatio ... c-local.md Pay close attention to the advice to include an ampersand (&) at the end of the command or the script will never finish and prevent full boot of the device.

I'll try this and report back.

[DougieLawson]

cron doesn't run with your regular environment, it has a restricted PATH. So the usual solution to "I run foobar with cron and it doesn't work" is to ensure that you run /home/pi/foobar (fully qualified name) and every file it reads or writes is referenced as /home/pi/filetoread or /home/pi/filetowrite rather than ~/filetoread or ~/filetowrite or even filetoread or filetowrite.

You can also stick a bunch of echo or print statements in your script and when it's run by cron that stuff written to stdout gets sent to your id by email (assuming you have something like exim4 configured as a MTA).

[rpdom]

Going back to the original issue

The thing is I need this script to run every 2 minutes.
So I looked and find that linux as the crontab function which is made for that.
I tip "sudo crontab -e" and updated this file this way :

Code: Select all

# Edit this file to introduce tasks to be run by cron.
*/2 * * * * pi /home/pi/testcam.sh
#
# 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

Apart from the fact that you should add new lines after all those messages (that won't stop it working, it just looks silly), you've used the wrong crontab format.
The /etc/crontab file uses the fields:

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Minute Hour DayOfMonth Month DayOfWeek Userid Command

whilst the user crontabs (that you get with the crontab command) use

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Minute Hour DayOfMonth Month DayOfWeek Command

Note the lack of Userid?

Your crontab entry is trying to run the command "pi" every two minutes, with the parameter "/home/pi/testcam.sh".

What's more, by using "sudo" you are editing the root crontab, not the pi crontab.

What you should do is use sudo crontab -e again and delete that line, then use crontab -e (without sudo) and add the following line to the end of the file

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*/2 * * * * /home/pi/testcam.sh

[socialdefect]

To prevent multiple instances from being started you can add something like this to your script:

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Pid=`ps aux | grep $0 | awk '{ print $2 }'`

YourScript(){
  -- paste the script here ----
}

if [ -x $Pid ] ; then
    YourScript
else
   while kill -0 "$Pid"; do
            sleep 0.5
   done
    YourScript
fi

This is more failproof than running sleep. This won't prevent multiple instances from being started if the sync task takes more than 2 minutes but it will prevent multiple sync instances from running at the same time.

[tberry]

The script solution I posted above worked.

Thanks to rpdom for explaining the userid in cron issue. I had not noticed the difference and that is likely what was wrong with my job.

I will also include socialdefect's code to check and kill the process rather than sleep.

I have a different issue now with wput uploading only part of the jpg but will post in a separate thread on that issue if I can't find a solution.

Thanks for the help!