How to Create a Cron Job and Execute at a Given Time in Linux


In this article, we will teach you on – how to schedule a corn job to execute at a specific time.

General Syntax of a Cron Job

MIN       HOUR    Day of month    Month     Day of Week    Command
0-59       0-23       1-31        1-12           0-6     linux command or script

To see a list of Cron Jobs which exists on the machine, run the below command –

# crontab -l
no crontab for root

To add the new cron job, run the below command –

#crontab -e
no crontab for root - using an empty one
Select an editor. To change later, run 'select-editor'.
 1. /bin/ed
 2. /bin/nano <---- easiest
 3. /usr/bin/vim.basic
 4. /usr/bin/vim.tiny
Choose 1-4 [2]:2
# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
#
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
#
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
#
# For more information see the manual pages of crontab(5) and cron(8)
#
# m h dom mon dow command

Scheduling a Job For a Specific Time

The basic usage of Cron is to execute a job in a specific time as shown below. This will execute the full backup shell script (full-backup) on 20th April 06:40 PM.

40 18 20 04 * /home/backups/full-backup

Explanation

40 – 40th Minute
18 – 06 PM
20 – 20th Day
04 – 4th Month (April)
* – Every day of the week

 At the end of the configuration you will be able to run a script or command at a specific time every day, like this we can specify the time for multiple executions with comma separeted values.

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