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I want to use cron to hourly run a python program in Linux(ubuntu). I wrote a script called

cd Dropbox/NetworkProject/AMT_Crawler/
scrapy crawl AmtCrawler --set FEED_URI=data.json --set FEED_FORMAT=json

Then I used

crontab -e

and add a line like this

*/30 * * * * sh Dropbox/NetworkProject/AMT_Crawler/ 2>&1 >> /Dropbox/NetworkProject/AMT_Crawler/output.log

After this, I run

sudo /etc/init.d/cron start

in terminal. It said

Rather than invoking init scripts through /etc/init.d, use the service(8) utility, e.g. service cron start Since the script you are attempting to invoke has been converted to an Upstart job, you may also use the start(8) utility, e.g. start cron

So I run this

service cron start

Then there was an error:

start: Rejected send message, 1 matched rules; type="method_call", sender=":1.196" (uid=1000 pid=12574 comm="start cron ") interface="com.ubuntu.Upstart0_6.Job" member="Start" error name="(unset)" requested_reply="0" destination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init")

Now I'm stuck with this problem asking for some help.

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migrated from Nov 7 '11 at 23:57

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cron should be started, no need to start it. I think the error is because only root can manage cron, try using sudo – RC. Nov 7 '11 at 5:55
+RC Thanks. I used sudo and it worked. However, I didnt get the any result from the program. The output log file is that, but it's empty. – Archer Nov 7 '11 at 6:12
If has execute permission (chmod +x, then the sh should be unnecessary (but harmless). – Keith Thompson Nov 8 '11 at 0:10

4 Answers 4

*/30 * * * * sh Dropbox/NetworkProject/AMT_Crawler/ 2>&1 >> /Dropbox/NetworkProject/AMT_Crawler/output.log

You need the full path for your dropbox directory. It is not under /.

Try this (assuming the Dropbox directory is $HOME/Dropbox):

*/30 * * * * sh $HOME/Dropbox/NetworkProject/AMT_Crawler/ >> $HOME/Dropbox/NetworkProject/AMT_Crawler/output.log 2>&1

Note that this changes both references to the Dropbox directory. It also fixes the ordering of the redirection operators; see my (Keith Thompson's) answer.

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I don't know whether this is the whole problem, but your output redirections are reversed. Rather than:

command 2>&1 >> /path/to/output.log

(which redirects stderr to stdout and then redirects stdout, but not stderr to output.log), you need:

command >> /path/to/output.log 2>&1

As others have said, the service cron start command shouldn't be necessary; crond should already be running (as you've already confirmed by getting an empty log file).

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cron(8) is always running. You do not need to start or restart it when you make changes to your crontab(5) file using crontab -e:

   Additionally, cron checks each minute to see if its spool
   directory's modtime (or the modtime on /etc/crontab) has
   changed, and if it has, cron will then examine the modtime on
   all crontabs and reload those which have changed.  Thus cron
   need not be restarted whenever a crontab file is modified.
   Note that the crontab(1) command updates the modtime of the
   spool directory whenever it changes a crontab.

(The last sentence is the reason why it is always recommended to use the crontab(1) program when modifying your own crontab(5) file.)

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The problem is that I can't get result from the scheduled python program, while there was a output log file, but nothing in it. – Archer Nov 7 '11 at 6:22
Cool, that's a result. Is Dropbox/NetworkProject/AMT_Crawler/ in the PATH of your crontab(5) file? If not, either give the full path to the executable in the crontab(5), or add the path to the PATH variable. – sarnold Nov 7 '11 at 6:58
yes, I have changed to the full path, but still not working. – Archer Nov 7 '11 at 7:13
Are there any errors in /var/log/* that look related? – sarnold Nov 7 '11 at 8:46

Try sudo service cron start.

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Now the cron can start. However, I didn't get any result from the scheduled python program. (I have tested the python program.) The output log file is there but nothing in it. – Archer Nov 7 '11 at 6:08

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