# CronJob Scheduler #

A cron job is a Linux command for scheduling script on your server to complete repetitive tasks automatically. Scripts executed as a cron job are typically used to modify files, databases and manage caching.

Cron is controlled by "crontabs". There is the master file in /etc/crontab. Each user's cronjob is stored in /var/spool/cron/username directory.


Benefits of Cron

·                     Cron already built, and works, very reliable

·                     You more easily have control over when it runs. You control the minute, hour, day, month and weekday  etc.

·                     You can run many cron with difference of 15 seconds

·                     You can manage cronjob from admin panel

·                     Need not run manually, Schedule once will execute manually.

Install crontab

crontab -a filename

Edit the crontab

$ crontab -e

Display crontab

crontab -l

Display the last edit the crontab file

crontab -v

Remove crontab

crontab -r

Following are the syntax for cron
minute(s) hour(s) day(s) month(s) weekday(s) command(s) "Argument1" "Argument2"

1 * 3 4 5 /path/to/command arg1 arg2

If you don't have parameter put star (*)


Description of Cron fields

Field        Description

minute(0-59) The exact minute that the command sequence executes
hour (0-23) The hour of the day that the command sequence executes
day(1-31)   The day of the month that the command sequence executes
month(1-12) The month of the year that the command sequence executes
weekday(0-6)         The day of the week that the command sequence executes (Sunday = 0, Monday = 1, Tuesday = 2, and so forth)
command(s) File Path    Absolute path CronFile
Argument               Argument (IF you want to pass an argument)