Every minute cron goes through all the crontabs and looks for the jobs that should be executed. The exact time of the execution can be specified using the cron syntax. Whenever the parameter matches the current date and time cron job is executed.
# Example of job definition:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23)
# | | .---------- day of month (1 - 31)
# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...
# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# | | | | |
# * * * * * command to be executed
* * * * * echo 'Hello world!'
You can use certain operators to specify the time:
*is used as any value-is used to state the range of values (e.g.1 - 5),is used to specify multiple values/is used to specify step values that can be used in conjunction with ranges (e.g.1-10/2is the same as1,3,5,7,9)
Every 5 minutes
*/5 * * * * echo 'Hello world!'
Every 10 minutes
*/10 * * * * echo 'Hello world!'
Every 15 minutes
*/15 * * * * echo 'Hello world!'
Every 30 minutes
*/30 * * * * echo 'Hello world!'
Using the */n you can specify the time of the jobs that will be executed every
n minutes.
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How to run cron jobs every 5, 10, or 30 seconds?
By default, cron checks crontabs for cronjobs every minute. If you want to run a job every n seconds you need to use a simple workaround.
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Cron can generate logs, which are very useful in troubleshooting your cron jobs. In this quick tutorial, we will take a look at cron logs – how to find them and how to read them.
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