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Old 02-22-2011, 11:58 AM   #1
littlebigman
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Question [cron] Adding job through script?


Hello,

I need to add a job to contrab from a script. Appending the following line to /etc/crontab doesn't do anything:

Code:
# cat /etc/crontab
...
*/1 * * * * root /tmp/myscript.sh

# crontab -l
no crontab for root
Is there a way to automate adding jobs to cron?

Thank you.
 
Old 02-22-2011, 12:20 PM   #2
d072330
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Easiest way is to just type crontab -e as the user you want the cron job to run as and then enter your script and then save it. Then your crontab -l should list your job.

Last edited by d072330; 02-22-2011 at 12:23 PM.
 
Old 02-22-2011, 12:27 PM   #3
Dark_Helmet
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Two things:

1. Your use of "*/1" is unnecessary. Unless I'm mistaken, all you need is the asterisk.

2. /etc/crontab is not root's crontab. The root user has a user-based crontab just like any other user. The /etc/crontab file and the files in /etc/cron.d are system-wide crontab files that are not associated with a specific user--they are generic "system" crontabs. They do not require use of the crontab command to install or modify.

So, appending a line to /etc/crontab, such as:
Code:
* * * * * root /tmp/myscript.sh
should work to run /tmp/myscript.sh as root once every minute.

Note, you will not be able to see the job listed under root or any other user's crontab by using "crontab -l"

EDIT:
If you do not believe the script is running, then check that your script uses absolute paths to programs and/or have the script write information to a log file to verify it is working.

EDIT2:
You can read more by using man 5 crontab -- the comments in the example crontab files explain that /etc/crontab is a "system" crontab file.

Last edited by Dark_Helmet; 02-22-2011 at 12:36 PM.
 
Old 02-22-2011, 12:34 PM   #4
colucix
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In alternative, if you want to update the user's crontab through script you can simply do:
Code:
#!/bin/bash
(crontab -l 2>/dev/null; echo "* * * * * /tmp/myscript.sh") | crontab -
where redirection of standard error to /dev/null prevents the printing out of "no crontab for root" message if it is initially empty.
 
Old 02-22-2011, 03:05 PM   #5
benq70
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Proceed with adding your cron entry: * * * * * /tmp/myscript.sh

Then just modify /tmp/myscript.sh to do your bidding. That way you don't need to touch your cron afterwards.

If you need to verify that your script was executed look in /var/log/cron(or equivalent) or execute "touch /tmp/myscript.`date +%m-%d-%y-%H-%M-%S`" within /tmp/myscript.sh or something similar.

Long term I usually have my scripts send output to a log file for troubleshooting purposes like "echo blah blah >>/home/me/logs/logfile.log"

Hope this helps.
 
Old 02-28-2011, 07:31 AM   #6
littlebigman
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Thanks for the help.
 
  


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