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How to set Cron/At Access Control

Cron stores it's enteries in the crontab (cron table) file. This is generally located in your /etc directory. As well, each user on your system can have their own crontab which would be stored in /var/spool/cron/. To edit a users crontab entry, simply log into your system for that particular user and type crontab -e. The default editor for the 'crontab -e' command is vi. Below is the simple example of crontab entry

0 12  *  *  *  root  php /srv/www/mysar/dump.php >> /dev/null 2>&1

1Minute (0-59)
2Hour (2-24)
3Day of month (1-31)
4Month (1-12, Jan, Feb, etc)
5Day of week (0-6) 0 = Sunday, 1 = Monday etc or Sun, Mon, etc)
6Run the command as following user
7Command to execute

Now to control the access to crontab for particular user you need to edit the required configuration file depending upon your requirement, which are mentioned below.

1.  /etc/cron.allow
      If it exists, a user must be listed in this file in order to use crontab.

2. /etc/cron.deny
      If it exists, a user must not be listed in this file in order to user crontab.

Similary for "at" access control, you can edit the following files depending upon your requirement

1. /etc/at.allow
      Same as cron.allow, only for "at".

2. /etc/at.deny
      Same as cron.deny, only for "at".


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