Scheduling Tasks

Learn how to schedule tasks and job in RHEL8.

Cron :

Cron is a daemon that triggers jobs on a specific time, the cron is mostly used for regular re-occurring jobs, systemd timer is the new alternative for cron. Scripts are executed on an hourly,daily,weekly,monthly basis. You can find all the generic time-specific cron jobs within /etc/cron.d Lemme show you how to schedule a job using cron : -> crontab -e or we can create a file under /etc/cron.d/ -> Then, we will have to define the job, take a quick view on /etc/crontab if you forget the format. -> verify using crontab -l -> crontab -r if you wish to clear the crontab task. -> a file is created under /var/spool/cron for each user. Below, I will show you some jobs created with cron :

You can use "@" as shortcut if you are scheduling a job hourly-daily...etc Cron does not have STDOUT, Hence, you can't use echo, instead you can use logger. Consult man 5 crontab for more information.

anacron :

anacron is the service behind cron to execute a cron job on a regular basis, but not in a specific time. it can be used to control the execution of daily, weekly and monthly jobs or anything with period of n day. You can find the configuration file under /etc/anacrontab. Let me show you a quick example :

vim /etc/anacrontab   
            ##Job-description lines can have the following format

          period in days   delay in minutes   job-identifier   command
cat /etc/anacrontab
        1       15      my.daily      /usr/bin/yum update -y

at :

used for jobs that need to be started once. atd is the service behind running the once-started jobs. Now lets see how at works : -> at <time> example : at 3pm today -> task example : echo " Hello World" > /root/example.txt -> CTRL+D -> to save and quit the interface. -> atq -> to list the pending jobs -> atrm <job_nb> -> to remove a scheduled