Aug 05









So you need to run some script that you’ve created at certain times on certain days and you don’t know anything about cron.  You’ve come to the right place.  I am about to show you the basics of the Unix/Linux crontab:

Below are some basic crontab commands:

export EDITOR=vi – This sets up a default editor for the crontab to use.

crontab -e     Edit your crontab file, or create one if it doesn’t already exist.

crontab -l      Display your crontab file.

crontab -r      Remove your crontab file.

crontab -v      Display the last time you edited your crontab file.

crontab syntax:

A crontab file has five fields for specifying day , date and time  followed by the command to be run at that interval.

*     *   *   *    *  command to be executed

-     -    -    -    -

|     |     |     |     |

|     |     |     |     +—– day of week (0 – 6) (Sunday=0)

|     |     |     +——- month (1 – 12)

|     |     +——— day of month (1 – 31)

|     +———– hour (0 – 23)

+————- min (0 – 59)

Sample crontab entry to run a the unix remove command to remove some temporary files:

30     *     *     *     *         rm /tmp/*.tmp

This runs a rm comand and removes all files that end in .tmp from the /tmp directory every 30 minutes.

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