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Crontab is a program and need to install on system it is also used to drive the cron daemon. Each user uses their own crontab and command. As a system admin always we need to execute some commands every-time. So it’s very difficult to run these commands manually. Cron is used to execute desired command in background at scheduled time.
In this tutorial I am going to explain how we can install crontab on CentOS/Redhat/Fedora or Ubuntu/Debian.
Follow this tutorial to know more about crontab example : Top 20 Crontab Example to Schedule Task
You will get below error if you try to execute crontab -l command on your system means there is no crontab is installed on your system.
# crontab -l -bash: crontab: command not found
To install crontab command you will need to install cronie packages on CentOS/Redhat/Fedora system. You can install it from yum command. Using yum command it will install required dependencies.
Install or Setup Cron on CentOS/Redhat/Fedora
Run this below command to install cronie on your RHEL System
# yum install cronie
You will get some output like below.
Loading mirror speeds from cached hostfile epel/metalink | 4.0 kB 00:00 * base: mirror.tadu.vn * epel: mirror.lzu.edu.cn * extras: mirror.dhakacom.com * updates: mirror.dhakacom.com base | 3.7 kB 00:00 epel | 4.3 kB 00:00 epel/primary_db | 5.0 MB 00:14 extras | 3.3 kB 00:00 mysql-connectors-community | 2.5 kB 00:00 mysql-tools-community | 2.5 kB 00:00 mysql56-community | 2.5 kB 00:00 mysql56-community/primary_db | 126 kB 00:00 updates | 3.4 kB 00:00 updates/primary_db | 4.1 MB 00:08 vz-base | 951 B 00:00 vz-updates | 951 B 00:00 Resolving Dependencies --> Running transaction check ---> Package cronie.i686 0:1.4.4-16.el6_8.2 will be installed --> Processing Dependency: dailyjobs for package: cronie-1.4.4-16.el6_8.2.i686 --> Processing Dependency: /usr/sbin/sendmail for package: cronie-1.4.4-16.el6_8.2.i686 --> Running transaction check ---> Package cronie-anacron.i686 0:1.4.4-16.el6_8.2 will be installed --> Processing Dependency: crontabs for package: cronie-anacron-1.4.4-16.el6_8.2.i686 ---> Package exim.i686 0:4.84.2-3.el6 will be installed --> Running transaction check ---> Package crontabs.noarch 0:1.10-33.el6 will be installed --> Finished Dependency Resolution Dependencies Resolved ====================================================================================================================================== Package Arch Version Repository Size ====================================================================================================================================== Installing: cronie i686 1.4.4-16.el6_8.2 updates 74 k Installing for dependencies: cronie-anacron i686 1.4.4-16.el6_8.2 updates 31 k crontabs noarch 1.10-33.el6 base 10 k exim i686 4.84.2-3.el6 epel 1.3 M Transaction Summary ====================================================================================================================================== Install 4 Package(s) Total download size: 1.4 M Installed size: 4.2 M Is this ok [y/N]: y Downloading Packages: (1/4): cronie-1.4.4-16.el6_8.2.i686.rpm | 74 kB 00:01 (2/4): cronie-anacron-1.4.4-16.el6_8.2.i686.rpm | 31 kB 00:00 (3/4): crontabs-1.10-33.el6.noarch.rpm | 10 kB 00:00 (4/4): exim-4.84.2-3.el6.i686.rpm | 1.3 MB 00:10 -------------------------------------------------------------------------------------------------------------------------------------- Total 78 kB/s | 1.4 MB 00:18 Running rpm_check_debug Running Transaction Test Transaction Test Succeeded Running Transaction Installing : exim-4.84.2-3.el6.i686 1/4 Installing : cronie-anacron-1.4.4-16.el6_8.2.i686 2/4 Installing : cronie-1.4.4-16.el6_8.2.i686 3/4 Installing : crontabs-1.10-33.el6.noarch 4/4 Verifying : cronie-1.4.4-16.el6_8.2.i686 1/4 Verifying : cronie-anacron-1.4.4-16.el6_8.2.i686 2/4 Verifying : crontabs-1.10-33.el6.noarch 3/4 Verifying : exim-4.84.2-3.el6.i686 4/4 Installed: cronie.i686 0:1.4.4-16.el6_8.2 Dependency Installed: cronie-anacron.i686 0:1.4.4-16.el6_8.2 crontabs.noarch 0:1.10-33.el6 exim.i686 0:4.84.2-3.el6 Complete!
Adding a New Cron Job in Crontab
You can add new job using crontab -e command. It will open in default editor you will need to edit it. Crons are saved in /var/spool/cront/username file. Follow this below command to add new cron job.
# crontab -e 0 3 * * * zip -r cron-all-backup.zip /var/spool/cron/crontabs/
In above example we scheduled crontabs backup everyday at 3 ‘O’ clock.
Listing all Crontab Entry or Jobs
With -l options we can list all scheduled jobs. Follow the below command to list all scheduled jobs for current logged in user.
# crontab -l 0 3 * * * zip -r cron-all-backup.zip /var/spool/cron/crontabs/ 5 1 * * * /roob/scripts/daily-backup.sh
Listing Specific User’s Crontab Entry or Jobs
Follow this below command to list specific user crontab entry or jobs.
# crontab -u ram(username) -l 0 3 * * * zip -r cron-all-backup.zip /var/spool/cron/crontabs/
Install or Setup Cron on Ubuntu/Debian System
To install or setup Cron on your Ubuntu/Debian system you will need to install cron packages on Ubuntu/Debian system.
Follow these steps to setup or install cron job on Ubuntu/Debian system.
Let’s first update your system package to latest version. Follow this below command to update your current installed packages.
# apt-get update Or # apt-get upgrade
Check if Cron Package Installed
Run this below command to check cron package is installed or not:
# dpkg -l cron
if cron is not installed, run this below command to install it.
# apt-get install cron
Verify Cron Service is Running or not
# service cron status
Follow these below command to stop start cron service:
To Stop
# service cron stop
To Start
# service cron start
Configure Cron Job on Ubuntu/Debian
To configure cron job you need to modify /etc/crontab file using nano editor to modify this file you need sudo permission.
# nano /etc/crontab 0 3 * * * zip -r cron-all-backup.zip /var/spool/cron/crontabs/
I hope this article will be helpful to install crontab on Redhat.x and CentOs.x system.
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