cron jobs general

cron_jobs_general.txt

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tail -f /var/log/syslog
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#min hour day month weekday command

*/1   *    *    *    *     <your command>


#weekdays at 9am
0 9 * * 1-5 /home/user/hello_script.sh

crontab -e
 
*/1 * * * * echo "job every minute"

==================================================================

*/1 * * * * /usr/bin/wget -O /dev/null http://example.com/cron.php

Any difference between * and */1?

 	
CLI mode vs. calling http URLS

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1 * * * * /path/to/command


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You could tell wget to not download the contents in a couple of different ways:

wget --spider http://www.example.com/cronit.php

which will just perform a HEAD request but probably do what you want

wget -O /dev/null http://www.example.com/cronit.php

which will save the output to /dev/null (a black hole)

You might want to look at wget's -q switch too which prevents it from creating output

I think that the best option would probably be:

wget -q --spider http://www.example.com/cronit.php

that's unless you have some special logic checking the HTTP method used to request the page


Matt Cutts: Gadgets, Google, and SEO
How to fetch a url with curl or wget silently
Posted January 3, 2007 in How to, Linux/Ubuntu, Productivity

Cron jobs need quiet operation; if a command generates output, you’ll get an email from cron with the command output. So if you want to fetch a file silently with wget or curl, use a command like this:

curl –silent –output output_filename http://example.com/urltofetch.html

wget –quiet –output-document output_filename http://example.com/urltofetch.html

There are shorter versions of these options, but using the verbose options will make code or cron jobs easier to understand if you come back to them. Be aware that urls with “&” in them can confuse wget at least, so depending on your shell (bash, csh, tcsh), you may need to put single or double quotes around the url.

This would trigger the cron only when it's 1 minute after an hour. I.e. 1:01, 2:01 etc.