There are a couple ways to set up a cron job. If you have a script that you want to run ever so often, you could drop it in one of the cron directories, like cron.daily, or cron.weekly. These are located in /etc. Another way to do it is to use crontab.
To setup a cron job in crontab type
*/30 * * * * /path/to/yourscript.sh
The “*/30” makes the script run every 30 minutes. Below gives you a better idea of how the line works. The asterisk (*) specifies all possible values for a field, but can/should be replaced with the time you want the script to execute.
* * * * * command to be executed *(min) *(hr) *(DoM) *(month) *(week) /path/to/command_or_script.sh
- min= Minute 0 – 50
- hr = Hour 0-59
- DoM = Day of month 0-31
- month = Month 1-12
- week = Day of Week 0-7, Sunday is 0 or 7
Below are a couple of examples of how to run a script or command.
* * * * * /path/to/script.sh
Every day 10 minutes after 1 in the morning,
10 1 * * * /path/to/command
Also, if you don’t want to be emailed the output of the command, you can simple append “>/dev/null 2>&1” to the end of the crontab line.
0 * 1 * * /path/to/command/ >/dev/null 2>&1