Author: Surendra Anne

The crontab is the default scheduling Application/program in most of the Linux/Nix boxes. Crontab is a scheduling tool for programs/scripts/applications to run at defined intervals without administrator interventions. Crontab = (Cron)oligical+(tab)le is nothing but time-table for executing some scripts at a given point of time So where we require crontab? Where there is no need for admin intervention such as taking daily backups, sending mails to particular user, monitoring network etc. Coming to scheduling task, crontab uses clock daemon (/usr/sbin/cron or /usr/sbin/crond) that executes commands at specific times. The corn table for each user is located in /var/spool/cron/ with their names suppose if you want to see cron table for root then the file you have to look for cron job for root is /var/spool/cron/root. Crontab file content The content of the file can be divided in to 6 fields(first 5 for specifying time and last one for executing scripts/app etc) The first five fields are separated by either a space or a tab and represent the following unit’s, respectively: * minutes (0-59) * hour (0-23) * day of the month (1-31) * month of the year (1-12) * day of the week (0-6, 0=Sunday) Configuration of crontab for user Example 1: Creating crontab for a user #crontab -e -u username -e is for specifying editing and -u for specifying user name when you are scheduling crontabs for other users if users want to...