Introduction to crontab
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In this tutorial, Jeff shows you the basics of crontab. Learn what they are, how to set one up, and even how to have it email you!

By : Jeff Johnson

The tutorial is about using crontab.Q: What is crontab?A: crontab is a program that runs commands at specified timesQ: So what do i need?A: You need a connection to a *nix box that has crontab installed

More things to read: FreeBSD Man page, 2

Starting off

In this tutorial we will be using `ee` to edit are files. If you want the change the editor crontab uses type:

`EDITOR=[some editor]`

Now lets make our first crontab entry:

$ crontab -e 30 4 13 12 * /root/databasebackup

Enter in that then save and exit (ee users: exc then enter). You should see:

crontab: installing new crontab

Now you may wounder what you just did?Line 1: Your ran the crontab program and told it you wanted to edit your crontab file.Line 2: You entered a string to tell crontab when to run the program.

Here's what the numbers and stars ment:

|- Run the 30'th minite  |   |- Run on the 4th hour  |   |   |- Run on the 13th day  |   |   |    |-Run on the 12th month  |   |   |    |   |-Run on any day of the month  |   |   |    |   |  |-Run this command 30   4   13   12  *  /root/databasebackup

This will run on: 4:30am December 13th once a year on any day of the week.

Now you probably will not want to run something once a year, most likely once a day/week/month. If you want to run something the 4th hour of every day and the 30th minute you would put:

30 4 * * * <command>

If you want to run a command on the 30th minnte of every hour, but only on Sunday you would put:

30 * * * 0 <command>

Another thing is to make it run at a certain interval by putting a *[number]/ in place of the number. To run a command every 10 minutes you would put:

*10/ * * * * <command>

Next: Sending the output >>
 

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