Crontab / Cron / Cron Job Usage

This page answers questions like these:

How run a cronjob every few hours?
How run a cronjob weekly?
How run a cronjob on the second Wednesday of every month?
How run a cronjob on the third Friday of every month?

Useful Comment Block for the Top of a Crontab File:

# The fields below can be a star (i.e. *) meaning any value, a single number # (e.g. 2), a range (e.g. 4-6), or a list of numbers and ranges (e.g. 1,3-5,7). # Comment lines must start with #. # #Minute (0 to 59). #| Hour (0 to 23: 0=Midnight, 12=Midday, 23=11pm). #| | Day of the month (1 to 31). #| | | Month of the year (1 to 12: 1=January, 12=December). #| | | | Day of the week (0 to 6: 0=Sunday, 6=Saturday). #| | | | | Shell command to be executed. #| | | | | |

Run a Cron Job every 6 hours:

00 0,6,12,18 * * * COMMAND

Run the command COMMAND every day at 0:00, 6:00, 12:00, and 18:00.
Caveats: For security reasons, you may want to include the full path for the COMMAND command.

Run a Cron Job every Saturday:

15 12 * * 6 COMMAND

Run the command COMMAND every Saturday(6) at 12:15.
Caveats: For security reasons, you may want to include the full path for the COMMAND command.

Run a Cron Job on the First Day of the Month and every Sunday:

30 10 1 * 0 COMMAND

Run the command COMMAND at 10:30 on the 1^st day of every month and on every Sunday(0) of every month.
Caveats: For security reasons, you may want to include the full path for the COMMAND command.

Run a Cron Job on the First Sunday of every Month:

45 12 1-7 * * test "`date +\%w`" -eq 0 && COMMAND

Run the command COMMAND on the first Sunday(0) at 12:45.
Explanation: The first Sunday of any month will occur sometime between the 1^st and the 7^th of that month. The cron job runs from the 1-7 of every month. The test command stops the COMMAND running except on Sunday(0).
Caveats: Any % appearing in COMMAND must be backslashed. For security reasons, you may want to include the full paths for the test, date, and COMMAND commands.

Run a Cron Job on the Fourth Friday of every month:

00 12 22-28 * * test "`date +\%w`" -eq 5 && COMMAND

Run the command COMMAND on the fourth Friday(5) at 12:00.
Explanation: The fourth Friday of any month will occur sometime between the 22^nd and 28^th of that month. The cron job runs from the 22-28 of every month. The test command stops the COMMAND running except on Friday(5).
Caveats: Any % appearing in COMMAND must be backslashed. For security reasons, you may want to include the full paths for the test, date, and COMMAND commands.

Related Links:
Yesterday's Date using Shell Script Commands
Tomorrow's Date using Shell Script Commands
What Day of the Week Was It?
Is this Year a Leap Year? (using Shell Script Commands)

Home > Linux / Unix > Crontab / Cron / Cron Job Usage

Tags: cron, crontab, cron job, cronjob, cron security, cronjob security, cron job security, linux, unix, solaris, bsd, aix

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