[Linux] Crontab every 5 minutes

Well, if you are searching How to set a cron job? or want to schedules to run a cron job every 5 minutes. Then proceed reading.
Here, I will show how to schedule a cron and run that every five minutes to execute some desired results.

To edit the crontab i use the following command:

$ crontab -e

To list my currnet crontab

$ crontab -l

The following is the format entries in a crontab must be. Note all lines starting with # are ignored, comments.

So in terminal print ‘Hello’ every 5 minutes..

# MIN   HOUR   MDAY  MON  DOW   COMMAND 
   */5     *      *     *    *    echo 'Hello' 

MIN Minute 0-60
HOUR Hour [24-hour clock] 0-23
MDAY Day of Month 1-31
MON Month 1-12 OR jan,feb,mar,apr …
DOW Day of Week 0-6 OR
sun,mon,tue,wed,thu,fri,sat
COMMAND Command to be run Any valid command-line

Examples

Here are a few examples, to see what some entries look like.

#Run command at 7:00am each weekday [mon-fri]
00 07 * * 1-5 mail_pager.script ‘Wake Up’

#Run command on 1st of each month, at 5:30pm
30 17 1 * * pay_rent.script

#Run command at 8:00am,10:00am and 2:00pm every day
00 8,10,14 * * * do_something.script

#Run command every 5 minutes during market hours
*/5 6-13 * * mon-fri get_stock_quote.script

#Run command every 3-hours while awake
0 7-23/3 * * * drink_water.script

Special Characters in Crontab

You can use an

asterisk

in any category to mean for every item, such as every day or every month.

You can use commas in any category to specify multiple values. For example: mon,wed,fri

You can use dashes to specify ranges. For example: mon-fri, or 9-17

You can use forward slash to specify a repeating range. For example: */5 for every five minutes, hours, days
Special Entries

There are several special entries, some which are just shortcuts, that you can use instead of specifying the full cron entry.

The most useful of these is probably @reboot which allows you to run a command each time the computer gets reboot. This could be useful if you want to start up a server or daemon under a particular user, or if you do not have access to the rc.d/init.d files.

Example Usage:

# restart freevo servers
@reboot freevo webserver start
@reboot freevo recordserver start

The complete list:

Entry	Description	Equivalent To
@reboot	Run once, at startup.	None
@yearly	Run once a year	0 0 1 1 *
@annually	(same as @yearly)	0 0 1 1 *
@monthly	Run once a month	0 0 1 * *
@weekly	Run once a week	0 0 * * 0
@daily	Run once a day	0 0 * * *
@midnight	(same as @daily)	0 0 * * *
@hourly	Run once an hour	0 * * * *

Miscelleanous Issues

Script Output
If there is any output from your script or command it will be sent to that user’s e-mail account, on that box. Using the default mailer which must be setup properly.

You can set the variable MAILTO in the crontab to specify a separate e-mail address to use. For example:
MAILTO=”admin@mydomain.com”

Redirect Output to /dev/null
You can redirect the output from a cron script to /dev/null which just throws it away. By redirecting to /dev/null you will not receive anything from the script, even if it is throwing errors.
* * * * * /script/every_minute.pl > /dev/null 2>&1

Missed Schedule Time
Cron does not run a command if it was missed. Your computer must be running for cron to run the job at the time it is scheduled. For example, if you have a 1:00am scheduled job and your computer was off at that time, it will not run the missed job in the morning when you turn it on.

Related Links
[mkaz.com] At Command Mac OS X and eBay – at is similar to cron but for one time jobs, not reoccuring

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