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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 # 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
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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