The Cron daemon is a built-in Linux utility that runs processes on your system at a scheduled time.
By using a specific syntax, you can configure a cron job to schedule scripts or other commands to run automatically.
Basically, Cron is a utility that is used to schedule jobs according to a specific week, month, day, time, or time intervals. It is a time-based job scheduler that is pre-installed in Unix-like operating systems: Mac and Linux.
Here at LinuxAPT, as part of our Server Management Services, we regularly help our Customers to perform Ubuntu related queries.
In this context, we shall look into how to use Cron to schedule a job to run every hour on Ubuntu 20.04 LTS (Focal Fossa).
To do this, you need to log into the server as the root user with sudo rights.
Then, We need a small script that can be run as a job by Cron.
For this purpose, we have used the date command in our script. The output of a command is date and time which is routed to file.txt using >> directive.
date >> file.txtOpen a file (we name it demo.sh here). Write this snippet in the file, save, and exit. The file will be saved in our current directory which is /home/linuxapt/
The jobs that are already scheduled in the crontab can be enlisted using the following command:
$ crontab –lSince we are enlisting the jobs here before initiating any, it reasonably prompts "no crontab for user".
Let us add our first cron job now.
The parameter –e is used to add a new job to cron:
$ crontab -eThis will open the Crontab text editor where you can input the cron values.
Here, Scroll down to the bottom of the file using the keyboard.
i. Now we will add our command:
0 */1 * * * /bin/sh /home/linuxapt/demo.shThe first entity represents that the job should execute at the zeroth minute.
The second entity represents that it should run after an interval of an hour.
Shell in which script is coded and the script itself is mentioned in the next sections of the job.
ii. After writing it in the file, you can Save and close the file.
We will use cat utility to observe the results. The utility dumps the content of the file on the command line.
$ cat file.txtHere, you will see that the utility runs as the hour begins and writes time with a date at the end of the file.
This article covers how a cron job can be scheduled to run every hour on Ubuntu System. Most Linux users are familiar with the Crontab job scheduler, which acts as a silent daemon that performs all the tasks assigned to it automatically, without any human intervention.
This job scheduler makes the life of a Linux user much easier, as the user can hand over all the frequently occurring tasks to the Crontab scheduler so that these tasks can be executed automatically according to a specified schedule.
To Start Crontab Service
Run the following command:
$ sudo systemctl start cron
To Check Status of Crontab Service
Execute the command:
$ sudo systemctl status cron
To Launch Crontab File:
Execute the command:
$ crontab –e
To Run a program or script every 5 or X minutes or hours on Linux:
1. Edit your cronjob file by running crontab -e command.
2. Add the following line for an every-5-minutes interval. */5 * * * * /path/to/script-or-program.
3. Save the file, and that is it.
