The cron daemon is a long running process that executes commands at specific dates and times. To schedule one-time only tasks with cron, use at or batch. For commands that need to be executed repeatedly (e.g. hourly, daily or weekly), use crontab, which has the following options:

The crontab command creates a crontab file containing commands and how often cron should execute them. Each entry in a crontab file consists of six fields, specified in the following order:

minute(s) hour(s) day(s) month(s) weekday(s) command(s)

The fields are separated by spaces or tabs. The first five are integer patterns and the sixth is the command to be executed. The following table briefly describes each of the fields:

Each of the patterns from the first five fields may either be an asterisk (*) (meaning all legal values) or a list of elements separated by commas. An element is either a number or two numbers separated by a minus sign (meaning an inclusive range). Note that the specification of days may be made by two fields (day of the month and day of the week). If both are specified as a list of elements, both are followed. For example:

MAILTO=user@domain.com
0 0 1,15 * 1 /big/dom/xdomain/cgi-bin/scriptname.cgi

The cron daemon would run the program scriptname.cgi in the cgi-bin directory on the first and fifteenth of each month, as well as on every Monday. To specify days by only one field, the other field should be set to *. For example:

MAILTO=user@domain.com
0 0 * * 1 /big/dom/xdomain/cgi-bin/scriptname.cgi

The program would then only run on Mondays.

If a cron job specified in your crontab entry produces any error messages when it runs, they will be reported to you via email.

You may create crontab files in notepad (being sure to upload them in ASCII) or you may create them from the command line (via SSH) by simply typing:

mcedit cronfile.txt

For more information, consult the man pages. man pages are the directions and tutorials available to you right at the command line. Type any of the following lines to open the relevant tutorials ([Enter] means to hit the Enter (return) key):

man 5 crontab [Enter]
man 1 crontab [Enter]
man cron [Enter]
man at [Enter]
man batch [Enter]
man 1 cron [Enter]

Note:Your crontab file must end with a line feed - in other words, make sure to press [Enter] after the last line in the file.

Try It!

Step 1: Create a simple text file using Notepad or any simple text editor that contains the following text:

MAILTO=yourusername@yourdomain.com [Enter]
58 23 * * * /big/dom/xdomain/cgi-bin/yourscript.pl
[Enter]

Notes for Step 1

1. You may create this file using your CNC File Manager by navigating to the /big/dom/xdomain/ directory and clicking 'Create New File' or any other simple text editor such as Notepad.
   
   
2. [Enter] should not actually be typed. [Enter] means hit the "Enter" (return) key to begin the next line and to add a blank line feed at the end of the last line of your cron file. It is important to always remember to do this.
   
   
3. MAILTO: Replace the email address with a valid email address of your own. This will ensure that when your cron runs, any output from the script, such as an error message, will be emailed to you.
   
   
4. The second line tells your server when to run this script. In this example, the script will be run at 11:58 PM Eastern Time every day of the year.
   
   
5. It is very important that you double-check the script path to ensure it is correct and remember the file names are CaSe-SeNsiTive.

Step 3: Upload the file in ASCII.
Any standard FTP client or your account's CNC upload feature will work for this. The file must be uploaded in ASCII mode and it is recommended that it be placed in your /big/dom/xdomain/ directory. It may be placed anywhere in your account but to prevent browser access (security risks) it is strongly recommended to place it above your /www directory.

crontab /big/dom/xdomain/cronfile.txt

The above tells the server's crontab where the file is located and that you wish to make it active. Make sure the path to the file is the actual path to where the file was placed. If successful, you will be returned to the command bash line. If not, an error will be displayed.

IMPORTANT NOTES

Removing/Stopping the Cron: Deleting the cronfile.txt file from your account will not stop the cron. You may remove this file at any time, however since the server's crontab already has the contents, the cron will still run once it has been made active.

crontab -r

The crontab -r will deactivate the cronjob and remove the file contents from the server.

Security Note: If the script the cron is set up to run is in the /cgi-bin/ or /www/ directory, it may be run at any time by anyone with browser access. If the crontab is all that should run the script and you do not want the public to be able to run the script, then you will need to place the script in a directory above the /cgi-bin/ and /www/ directories such as: /big/dom/xdom/user/cronscripts/scriptname