Cron.txt

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Creation-Date: 2017-01-14T02:47:43+01:00

====== Cron ======
Created Saturday 14 January 2017

**By default, Arch doesn't come with a Cron implementation. We'll be using **//cronie//** which handles scheduled jobs, even if the computer was shut down when the job was supposed to run.**

== Installation ==
$ pacman -S cronie

**# And enable its service file**
$ systemctl enable cronie.service

**# In order to use Cron, a user needs to be a member of the **//users//** group (not default)**
$ gpasswd --add stick users


===== Usage =====
**# If you installed **//SSMTP//** in the previous step, you will be notified when a job has been run**
**# Cron can be used in two ways - place executable Shell scripts in one of the job folders.**
**# This will execute the file in the appropriate time according to which folder the script is located**
**# Places for Shell executable **
	** # **///etc/cron.hourly//
	** # **///etc/cron.daily//
	** # **///etc/cron.weekly 		//

**# Or, you place a Cron command inside the crontab file, which is provided for each user.**
**# The basic format for Cron is; (separated with a space)**
	//<MINUTE>  <HOUR>  <DAY_OF_MONTH>  <MONTH>  <DAY_OF_WEEK>  <COMMAND>//
		**#** //<MINUTE> //**: from 0 to 59**
		**#** //<HOUR> //**: from 0 to 23**
		**#** //<DAY_OF_MONTH> //**: from 1 to 31**
		**#** //<MONTH> //**: from 1 to 12**
		**#** //<DAY_OF_WEEK> //**: 0 to 6  where 0 is Sunday**
		**#** //<COMMAND> //**: The command to run**
	
**# Cron also has some basic keywords;**
	//@reboot //**: at startup**
	//@yearly//** : once a year**
	//@annually //**: same as yearly**
	//@monthly //**: once a month**
	//@weekly //**: once a week**
	//@daily //**: once a day**
	//@midnight //**: same as daily**
	//@hourly //**: once an hour**
	
**# Ex;  **//@reboot ~/bin/i_love_cron.sh  //**will execute the script at startup**

== Basic Commands ==
**# To view Crontabs (tasks)**
$ contab -l

**# To edit Crontabs**
$ crontab -e

**# Or edit root jobs (system based) with sudo**
$ sudo crontab -e

**# To remove all Crontabs**
$ crontab -r

== Examples and further Syntax explained ==
**# Using the crontab/cron syntax**

**# * (star) is used as wildcard - ex, every hour, every day, every month (15min. past)**
15 * * * * someCommand

**# , (comman) is used to specify multiple time - ex, at 12 and 16 o'clock **
00 12,16 * * * someCommand

**# / (slash) to specify a interval - ex to run something every 10min.**
*/10 * * * * someCommand

**# - (subtract) is to specify a range - ex, 1215 daily, except the summer months (June, July & August)**
15 12 * 1-5,9-12 * someCommand