Cron is a time-based job scheduler in Unix or Unix-like pc operating systems. You should use Cron to schedule jobs, i.e. to execute instructions or shell scripts at specified occasions, dates, or intervals. This permits you, for instance, to automate system maintenance or management, to download files from the internet, or to ship emails on a daily basis. It is a daemon, i.e. a background process that always runs on the server. The tasks Cron is supposed to perform are called CronJobs. Initially, the name Cron comes from the Greek god of time “chronos”.
Application of CronJobs
CronJobs can be utilized for single commands or for the automated execution of periodically recurring sequential tasks, e.g. for cleaning up databases by removing out of date entries, log files, and feedback, or for creating regular statistics on the number of users of a website.
Different applications include updating RSS feeds, publishing new content to a website on a selected date, producing multiple invoices, or automated newsletter distribution. Likewise, the backup of a database could be scheduled using CronJobs.
Construction and syntax of a CronTab file
Cron uses particular configuration files, so-called CronTab files, which contain a list of cron jobs to be executed. CronTab stands for Cron Table. Every line in the CronTab file represents a CronJob. It looks similar to a row of columns separated by a space. Each line specifies when and the way usually a particular command or script must be executed.
In a CronTab file, empty lines or lines starting with , areas, or tabs are ignored. Lines starting with are considered consumer comments.
Active lines in a CronTab either declare an surroundings variable or define a CronJob. Comments aren’t allowed in active lines.
The CronTab file will be accessed in a command-line interpreter by typing “crontab-e”. The commands within the CronTab file and their runtime are checked by the Cron daemon, which executes them in the system background.
The primary five columns comprise time values which define when a command ought to be executed. These are, from left to right:
Minute, specified as 0 – 59
Hour, specified as 0 – 23
Day, specified as 1 – 31
Month, specified as 1 – 12
Weekday, specified as zero – 7, 0 or 7 are Sundays
For each of these values, the wildcard “” can be utilized for execution at any time (i.e. at any minute, hour, day, month or weekday), “/n” for execution each n (minutes, hours, etc.) and “n,x,y” for execution on / at n, x or y. The final column specifies the relative or absolute path of the script to be executed. The CronJob is performed when the minute, hour, month, and day of the month or weekday match the current time.
Significance for on-line marketing
With CronJobs, you may automate numerous tasks in on-line marketing, thus increasing efficiency. In addition to automating time-consuming tasks, CronJobs can be used, for instance, to create visitor statistics for a website and automatically ship these to a recipient at certain intervals. In conjunction with CMS, CronJobs can be used to automatically calculate metrics or send newsletters on particular dates as part of marketing campaigns.
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