Crontab

Crontab is the equivelant of the scheduler in Windows.

Crontab Commands

Command	Description
crontab -e	Edit your crontab file, or create one if it doesn't already exist.
crontab -l	List your crontab file.
crontab -r	Remove your crontab file.
crontab -v	Display the last time you edited your crontab file

Crontab File

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)

Example

of Specific Minutes

3,5,10-15,30,55-60 * * * * /command/to/run.sh

of every 4 hours

0 */4 * * * /command/to/run.sh

at boot

@reboot /command/to/run.sh

Disable Email Notifications

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 .

>/dev/null 2>&1

>	is for redirect
/dev/null	is a black hole where any data sent, will be discarded
2	is the file descriptor for Standard Error
&	is the symbol for file descriptor (without it, the following 1 would be considered a filename)
1	is the file descriptor for Standard Out

Therefore >/dev/null 2>&1 is redirect the output of your program to /dev/null. Include both the Standard Error and Standard Out.