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A cron job is an automated program for Unix and Linux systems that allows users to run commands at specific times and dates. It can be used for various tasks, including email reminders and database backups. Cron tabs are used to set up the job, with six fields indicating minutes, hours, days, months, days of the week, and commands. The job is written in a text file and uploaded to the system.
A cron job is an automated program developed for Unix and Linux systems.
Allows the user to run several commands at a specific time on a
exact date. A cron job is an important tool that can be used for anything from running scripts and reindexing a web page to providing backups for a database. A cron job can also be used as an email download reminder. The user only needs to set up the schedule once so that he can continuously complete the job.
If a web e-zine owner has over 100 email subscribers who read his publication on the 25th of each month, for example, a cron job could help deliver the information to each reader at the same time and date each month. Also, it can add new members to the website and remove those who unsubscribe while keeping the database.
A cron job is set up with cron tabs within a cron tab manager. Cron tabs are divided into six fields: minutes, hours, days, months, days of the week, and commands. The command field provides instructions to the computer. The minutes field goes from 0 to 59 and indicates the exact minute in which the command must be executed. The time is set between 0-23, with zero representing midnight.
The days of the week range from 0 to 7, with 0 and 7 representing Sunday. Some older systems, including some Unix systems, use 0 to 6 as days of the week, 0 being Sunday. Whitespace or tabs must separate each field. Commas are used when adding a list, while asterisks are added when the user does not want to specify a field. For the aforementioned web e-zine owner, for example, the cron job could be set up with an asterisk instead of the day of the week because the 25th of the month will not always fall on the same day of the week.
A cron job is written in a text file with a set of cron commands that the computer must adhere to. Preparing a cron job as a text file also makes it easier to edit the scripts later if needed. Also, the cron job can be set up to allow or deny specific users to edit the set cron tab. Once the text has been created for the cron job, it is followed by a .txt extension, such as Cron.txt. Then, the job is uploaded and the accompanying text file command will be read as “crontab cron.txt” before it takes effect on the web page.
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