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Scheduling the future linux tasks through Crontab

 



Scheduling the future linux tasks through Crontab:



export EDITOR=vi to specify a editor to open crontab file.


crontab -e: Edit crontab file, or create one if it doesn't already exist.


crontab -l : crontab list of cronjobs, display crontab file contents.


crontab -r :Remove your crontab file.


crontab -v :Display the last time you edited your crontab file. (This option is only available on a few systems.)


.................................................... 


Syntax of the Cron jobs:


* * * * *script/command


first *: minute (0-59)


second*: hour (0-23)


third *:day of the month (1-31)


fourth *: Month of the year (1-12)


fifth* : day of the week (0-6): 0 represents sunday.




.........,.............................. 


A line in crontab file like below removes the tmp files from /home/someuser/tmp each day at 6:30 PM.

30 18 * * * rm /home/someuser/tmp/*


Cronjob runnig everyhour:

00 * * * *  rm/home/someuser/tmp/



cron every hour to run at 15 minute of an hour..

15 * * * * rm /home/someuser/tmp/*



cron every minute:

* * * * * rm /home/someuser/tmp/*



If you want to run a script every minute at specific hour, change the value of hour field to specific value such as 11th hour.

* 11 * * *  rm /home/someuser/tmp/*



To collect the cron execution log in a file:

30 18 * * * rm /home/someuser/tmp/* >

/home/someuser/cronlogs/clean_tmp_dir.log


Crontab file location for redhat.centos.fedora: /var/spool/cron/

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