Automating tasks with Cron jobs

Hello, everyone we are back again and this time with a handy tutorial on how to schedule tasks with Cron jobs

What are Cron jobs?

Cron is utility software used for automating tasks on a server system.  “Cron” stands for chronological, jobs which are supposed to run at a particular time. So using a Cron job you could specify to run a script or a command at a specific time on a specific day, week and month.

Syntax to specify a Cron job:

To specify a Cron job, you have to specify the exact time at which you want the command to run. Here is the syntax you need to use to specify a job.

  1. The number of minutes after the hour (0 – 59)
  2. The hour in military time (0 – 23)
  3. The day of the month (1 – 31)
  4. The month (1 – 12)
  5. The day of the week (0 – 7)

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The Asterisk (*) Symbol:

As can be seen in the image above each asterisk symbol is a field and has a meaning, like the first “asterisk” is for the time in minutes. If you don’t want to specify a value for a field you can leave the Asterisk symbol there (*).

Example: If you want to specify a job that needs to run every month, then leave * in the fourth position that is the month field.

Here are a few examples with description to specify a job:

  1. 00  16  *  *  5  date

        The “date” command will run at 4:00 PM in the afternoon every “Friday” of every “Month”

     2. 30  16  *  12  5  date

        The “date” command will run at 4:30 PM in the afternoon every “Friday” in December

     3. 00  16  10  12  *  date

        The “date” command will run at 4:00 PM in the afternoon on the 10th of December.

     4. 00  16  10  12  5  date

         The “date” command will run at 4:00 PM in the afternoon if the 10th day was a Friday in       December.

With that cleared out, we can move on to the next segment of the article.

How to specify a Cron job?

  1. Open the crontab file using the command: sudo env EDITOR=nano crontab –e. (If you are comfortable using the vim editor, you can instead type the command crontab -e).
  2. If you want to schedule a single command to run periodically, you can specify that like this: 00  16  *  *  5  date. (This is an example job, you can change the fields according to your needs).

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    3. But if you want to schedule a particular script to run periodically you can do that in the      following steps:

  • Note down the path of the script you want to schedule.
  • Open the crontab file and write down the command: 00  16  *  *  5  /root/script.sh

NOTE: Replace /home/script.sh with the absolute path to your script file. Also change other fields like an hour, minutes as per your need.

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So that’s all on Cron jobs, hope this article helped, stay tuned with us for our next article.

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