Cron is a time-based mostly job scheduler in Unix or Unix-like pc working systems. You should use Cron to schedule jobs, i.e. to execute instructions or shell scripts at specified times, 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’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 instructions or for the automated execution of periodically recurring sequential tasks, e.g. for cleaning up databases by removing out of date entries, log files, and feedback, or for creating common statistics on the number of customers of a website.
Different applications include updating RSS feeds, publishing new content to a website on a specific date, generating a number of invoices, or automated newsletter distribution. Likewise, the backup of a database may be scheduled using 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. Every 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 needs to be executed.
In a CronTab file, empty lines or lines starting with , spaces, or tabs are ignored. Lines starting with are considered person comments.
Active lines in a CronTab either declare an surroundings variable or define a CronJob. Feedback should not allowed in active lines.
The CronTab file can be accessed in a command-line interpreter by typing “crontab-e”. The instructions in the CronTab file and their runtime are checked by the Cron daemon, which executes them in the system background.
The primary 5 columns contain 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 zero – 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 used 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.
Importance for on-line marketing
With CronJobs, you can automate numerous tasks in on-line marketing, thus rising efficiency. In addition to automating time-consuming tasks, CronJobs can be utilized, for example, to create visitor statistics for a website and automatically ship these to a recipient at sure intervals. In conjunction with CMS, CronJobs can be utilized to automatically calculate metrics or ship newsletters on particular dates as part of marketing campaigns.
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