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What is Cron Job and What Functions?

Senin, 11 Februari 20130 komentar


Anyone know about Cron Job? Cron Job is one of utility programs on Linux, actually Cron not only Linux, but also on Windows. Cron job used to execute commands automatically at a specific time or a specific course. Maybe a little different in windows system normally for Windows system we use to automate the execution of the file. Bat or it could be in the scheduler that is in the file and that program in a Linux or Unix system called Cron and to do so is called Cron Job execution. Scheduling system is available in Linux, which at the beginning of the birth of Unix Cron is contained in the current system - currently in the adoption of Linux operating systems.

Cron can be found on a web server Cpanel. This is used to execute Tasks / command - the command to be automatically executed by the web server, usually a Web server using the Linux and Unix operating systems have.

Cron was developed in the early release of V7 Unix, in 1979. And since it was developed, and the latest developments made by Redhat who forked (rewrite) the previous versions Cron Script. Project is named cronie Project, which was born in 2007 with Redhat as Sponsorhipnya. The results of this project put into operation the system of artificial RedHat. Project conducted a forked version of Vixie Cron on Script-Cron, a modern version of Cron. Vixie-Cron is a modern version of the previous Cron, Vixie-Cron was born in 1987 and written by Paul Vixie. And lastly the version 4 release in 2004.

Besides Conie Project released by Redhat, there is also a system cron like Anacron, dcron, and fcron. Until now Cron is still in use and development is used on a web server. And named webcron.

Cron is a daemon, or a system. So we just turn it on one time and he was automatically activated. To perform add, edit, or delete command CronJobs we should do it in a crontab. We can call him on the shell, by typing crontab. And do not forget to login as administrator.

Executed with a specific user

# Crontab-u

In this way, the cron job will be executed by the user are now in use. But if using a specific user, then it will be executed by the user Cron entered.

# Crontab-l-u linuxUser

Cron With this command will be executed using the user LinuxUser.

See the list in the Crontab

# Crontab-l

This way you will see a list of commands - commands in the crontab.

Editing Crontab

# Crontab-e

This command is used to edit commands - commands in the crontab.

# Crontab-e-u LinuxUser

Execution of the command crontab file

Sometimes to enter the crontab command we can menginputkannya of the file, rather than put us one by one. This way we can more easily and rapidly enter the crontab command.

Example:

# Cat home / root / listcrontab.txt

In the listcrontab.txt file there is a command - a command from crontab. And to put it in our crontab to execute the command in the shell.

# Crontab / home / root / listcrontab.txt

In this way the existing orders in listcrontab.txt be put into crontab. To check this we write the command to issue a list of crontb.

# Crontab-l

And to enter into a specific user, we simply add the user name in the command.

# Crontab-u LinuxUser / home / root / listcrontab.txt

Delete an existing crontab command.

To delete an existing crontab-r command we use.

# Crontab-r

In this way the existing crontab will be deleted. -R means remove. -I serves to confirm when will mengeksekui command.

# Crontab-ir

Crontab: root's crontab really delete? Y

This way before crontab deleted, the user will be prompted from there.
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