Cron is a time-based mostly job scheduler in Unix or Unix-like computer operating systems. You need to use Cron to schedule jobs, i.e. to execute commands or shell scripts at specified occasions, dates, or intervals. This allows you, for instance, to automate system maintenance or management, to download files from the internet, or to send emails on an everyday basis. It is a daemon, i.e. a background process that always runs on the server. The tasks Cron is meant 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 obsolete entries, log files, and comments, or for creating regular statistics on the number of customers of a website.
Different applications embody updating RSS feeds, publishing new content to a website on a particular date, producing multiple invoices, or automated newsletter distribution. Likewise, the backup of a database might be scheduled using CronJobs.
Structure and syntax of a CronTab file
Cron makes use of particular configuration files, so-called CronTab files, which include a list of cron jobs to be executed. CronTab stands for Cron Table. Every line within 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 typically a particular command or script needs to be executed.
In a CronTab file, empty lines or lines beginning with , spaces, or tabs are ignored. Lines beginning with are considered consumer comments.
Active lines in a CronTab either declare an setting variable or define a CronJob. Feedback will not be allowed in active lines.
The CronTab file might 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 within the system background.
The first five columns contain time values which define when a command ought to be executed. These are, from left to proper:
Minute, specified as 0 – fifty nine
Hour, specified as zero – 23
Day, specified as 1 – 31
Month, specified as 1 – 12
Weekday, specified as zero – 7, zero 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 every n (minutes, hours, etc.) and “n,x,y” for execution on / at n, x or y. The last 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 various tasks in online 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 send these to a recipient at sure intervals. In conjunction with CMS, CronJobs can be used to automatically calculate metrics or send newsletters on specific dates as part of marketing campaigns.
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