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 instructions or shell scripts at specified instances, 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 a regular basis. It’s a daemon, i.e. a background process that always runs on the server. The tasks Cron is supposed to perform are called CronJobs. Originally, 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 feedback, or for creating common statistics on the number of customers of a website.
Different applications embody updating RSS feeds, publishing new content material to a website on a specific date, generating a number of invoices, or automated newsletter distribution. Likewise, the backup of a database can be scheduled utilizing CronJobs.
Construction and syntax of a CronTab file
Cron uses particular configuration files, so-called CronTab files, which comprise a list of cron jobs to be executed. CronTab stands for Cron Table. Each line within the CronTab file represents a CronJob. It looks much like a row of columns separated by a space. Every line specifies when and how usually a particular command or script ought to be executed.
In a CronTab file, empty lines or lines starting with , areas, or tabs are ignored. Lines beginning with are considered user 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 could be accessed in a command-line interpreter by typing “crontab-e”. The commands in the CronTab file and their runtime are checked by the Cron daemon, which executes them in the system background.
The first five columns comprise time values which define when a command ought to be executed. These are, from left to proper:
Minute, specified as zero – 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 every of those values, the wildcard “” can be used 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 present time.
Importance for online marketing
With CronJobs, you may automate varied tasks in on-line marketing, thus increasing efficiency. In addition to automating time-consuming tasks, CronJobs can be utilized, 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 utilized to automatically calculate metrics or send newsletters on specific dates as part of marketing campaigns.
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