Linux – About using cron in Linux to schedule the python program

cronlinuxpython

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

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/script.sh 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.

Best Answer

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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