What is Cron?
Cron is the name of program that enables unix users to execute commands or
scripts (groups of commands) automatically at a specified time/date. This is enabled for all users on cias.rit.edu
To use cron for tasks meant to run only for your user profile, add entries to your own user’s crontab file. Start the crontab editor from a terminal window:
Edit the crontab using the format described in the next sections. Save your changes. (Exiting without saving will leave your crontab unchanged.)
Each of the sections is separated by a space, with the final section having one or more spaces in it. No spaces are allowed within Sections 1-5, only between them. Sections 1-5 are used to indicate when and how often you want the task to be executed. This is how a cron job is laid out:
minute (0-59), hour (0-23, 0 = midnight), day (1-31), month (1-12), weekday (0-6, 0 = Sunday), command
01 04 1 1 1 /usr/bin/somedirectory/somecommand
If you would like to say run a command every 10 minutes the format would be:
*/10 * * * * /usr/bin/somecommand
By default cron jobs sends a email to the user account executing the cronjob. If this is not needed put the following command At the end of the cron job line .
Generate log file
To collect the cron execution execution log in a file :
30 18 * * * rm /home/someuser/tmp/* > /home/someuser/cronlogs/clean_tmp_dir.log