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Cron is a time-based job scheduler that lets you schedule tasks and run scripts periodically at a fixed time, date, or interval. Moreover, these tasks are called cron jobs. With cron jobs, you can efficiently perform repetitive tasks like clearing cache, synchronizing data, system backup and maintenance, etc. These cron jobs also have other features like command automation, which can significantly reduce the chances of human errors. However, many Linux users face multiple issues while setting up a cron job. So, this article provides examples of how to set up a cron job in Linux. How To Set up a Cron Job Firstly, you must know about the crontab file to set up a cron job in Linux. You can access this file to view information about existing cron jobs and edit it to introduce new ones. Before directly opening the crontab file, use the below command to check that your system has the cron utility: sudo apt list cron If it does not provide an output as shown in the given image, install cron using: sudo apt-get install cron -y Now, verify that the cron service is active by using the command as follows: service cron status Once you are done, edit the crontab to start a new cron job: crontab -e The system will ask you to select a particular text editor. For example, we use the nano editor by entering ‘1’ as input. However, you can choose any of the editors because the factor affecting a cron job is its format, which we’ll explain in the next steps. After choosing an editor, the crontab file will open in a new window with basic instructions displayed at the top. Finally, append the following crontab expression in the file: * * * * * /path/script Here, each respective asterisk(*) indicates minutes, hours, daily, weekly, and monthly. This defines every aspect of time so that the cron job can execute smoothly at the scheduled time. Moreover, replace the terms path and script with the path containing the target script and the script’s name, respectively. Time Format to Schedule Cron Jobs As the time format discussed in the above command can be confusing, let’s discuss its format in brief: In the Minutes field, you can enter values in the range 0-59, where 0 and 59 represent the minutes visible on a clock. For an input number, like 9, the job will run at the 9th minute every hour. For Hours, you can input values ranging from 0 to 23. For instance, the value for 2 PM would be ’14.’ The Day of the Month can be anywhere between 1 and 31, where 1 and 31 again indicate the first and last Day of the Month. For value 17, the cron job will run on the 17th Day of every Month. In place of Month, you can enter the range 1 to 12, where 1 means January and 12 means December. The task will be executed only during the Month you specify here. Note: The value ‘*’ means every acceptable value. For example, if ‘*’ is used in place of the minutes’ field, the task will run every minute of the specified hour. For example, below is the expression to schedule a cron job for 9:30 AM every Tuesday: 30 9 * * 2 /path/script For example, to set up a cron job for 5 PM on weekends in April: 0 17 * 4 0,6-7 /path/script As the above command demonstrates, you can use a comma and a dash to provide multiple values in a field. So, the upcoming section will explain the use of various operators in a crontab expression. Arithmetic Operators for Cron Jobs Regardless of your experience in Linux, you’ll often need to automate jobs to run twice a year, thrice a month, and more. In this case, you can use operators to modify a single cron job to run at different times. Dash(-): You can specify a range of values using a dash. For instance, to set up a cron job from 12 AM to 12 PM, you can enter * 0-12 * * * /path/script. Forward Slash(/): A slash helps you divide a field’s acceptable values into multiple values. For example, to make a cron job run quarterly, you’ll enter * * * /3 * /path/script. Comma(,): A comma separates two different values in a single input field. For example, the cron expression for a task to be executed on Mondays and Wednesdays is * * * * 1,3 /path/script. Asterisk(*): As discussed above, the asterisk represents all values the input field accepts. It means an asterisk in place of the Month’s field will schedule a cron job for every Month. Commands to Manage a Cron Job Managing the cron jobs is also an essential aspect. Hence, here are a few commands you can use to list, edit, and delete a cron job: The l option is used to display the list of cron jobs. The r option removes all cron jobs. The e option edits the crontab file. All the users of your system get their separate crontab files. However, you can also perform the above operations on their files by adding their username between the commands– crontab -u username [options]. A Quick Wrap-up Executing repetitive tasks is a time-intensive process that reduces your efficiency as an administrator. Cron jobs let you automate tasks like running a script or commands at a specific time, reducing redundant workload. Hence, this article comprehensively explains how to create a cron job in Linux. Furthermore, we briefed the proper usage of the time format and the arithmetic operators using appropriate examples. View the full article

The post 5 Online Tools for Generating and Testing Cron Jobs for Linux first appeared on Tecmint: Linux Howtos, Tutorials & Guides .As a Linux system administrator, you can perform time-based scheduling of jobs/tasks using online cron job services or Cron, a powerful utility available in Unix/Linux The post 5 Online Tools for Generating and Testing Cron Jobs for Linux first appeared on Tecmint: Linux Howtos, Tutorials & Guides.View the full article

Zeit is an open-source GUI tool for scheduling jobs via “crontab” and “at”. It is written in C++ and released under GPL-3.0 License. It is an easy to use tool that provides a simple The post Zeit – A GUI Tool to Schedule Cron and At Jobs in Linux first appeared on Tecmint: Linux Howtos, Tutorials & Guides. View the full article

Whenever a Crontab job is executed, an email regarding the execution of that job is sent to the email address of the root user i.e. the email ID that you have provided while configuring your Cron daemon. These are the default settings of the Crontab service. However, in some situations, the users prefer to send these notifications to a location other than the root user’s email ID. You can consider a scenario in which a team lead has asked a subordinate to perform a job after every 4 hours. Whenever that subordinate performs that task, the team lead is supposed to report to the CEO about it, however, this will only be possible if the subordinate informs the team lead after every 4 hours that he has performed the assigned job. It means that if the subordinate forgets to do so, then the team lead will have to face the consequences. This task can be simplified if somehow the team lead automatically gets to know every time the subordinate performs that task without needing the subordinate to explicitly inform the team lead. Fortunately, the Crontab service in Linux allows us to do so by configuring its MAILTO parameter in such a way that it can send notifications to the desired recipient. So, today we will be talking about the method of configuring the Crontab MAILTO parameter to send notifications to a specified location other than the root user’s email ID in Linux Mint 20. Method of Configuring Crontab MAILTO Parameter to Send Notification to a Specified Location: For configuring the Crontab MAILTO parameter to send notifications to a specified location in Linux Mint 20, you are required to perform the following steps: Step # 1: Run the Crontab Service: First, you need to start the Crontab service so that it can perform the specified jobs by running the command stated below in your terminal: $ sudo systemctl start cron This command will immediately start the Cron daemon in the background. Step # 2: Verify the Working Status of the Crontab Service: To confirm the working status of the Crontab daemon, you can run the following command in your terminal: $ sudo systemctl status cron If the Crontab daemon is working, then you will see the “active (running)” status in the output of this command as highlighted in the image shown below: Step # 3: Open the Crontab File with the Nano editor: Now we will attempt to open the Crontab file to configure the MAILTO parameter by running the following command in the terminal: $ crontab –e By executing the crontab command, the crontab file will open with your default text editor i.e. the nano editor. Step # 4: Configure the MAILTO Parameter to Send Notification to a Specified Location: Now you can add any task to this file to be executed as a Crontab job. In our situation, we’ve built a Crontab job to execute a bash file every second. However, before that job, you need to enter the line shown below for configuring the MAILTO parameter for sending notifications to a specified location: MAILTO=”EmailAddress” Here, you need to replace the EmailAddress with the actual email ID of the person to whom you want to send the Crontab notifications. We wanted to send the Crontab notification to “aqsayasintw@gmail.com” as highlighted in the following image. At times, you have more than one job added to the Crontab file and you might want to send the notifications of each job to a different email address. In that case, you need to add the MAILTO line shown above before every job that you state in your Crontab file and just write the respective email address to where you want to send the notifications. In this way, you can easily configure the Crontab MAILTO parameter to send notifications to a specified location. Step # 5: Install New Crontab: Now you can close your Crontab file after saving it. As soon as you will do that, you will notice that the Cron daemon is installing the new Crontab since you have just modified the Crontab file by configuring the MAILTO parameter. Step # 6: Check whether the Crontab Job is Executing or Not: Moreover, if you also need to confirm that the job you have just added to your Crontab file is executing successfully or not, then you can even do that by running the following command in your terminal: $ sudo grep –a “Cron.sh” /var/log/syslog Here, Cron.sh is the name of the bash file that we wanted to execute every second whereas /var/log/syslog file in Linux contains a log of all the Crontab jobs that have been executed till the time you ran the above-mentioned command. When you will execute this command, you will notice in its output that the Cron.sh file is actually executing every second as shown in the image below. It also means that whenever this bash file will be executed, an email will be sent to the email address that has been stated with the MAILTO parameter in the Crontab file. Conclusion: By following all the steps explained in this article, one can easily configure the Crontab MAILTO parameter in such a way that it gets capable of sending notifications via email to any desired recipient. The MAILTO parameter can be configured for as many recipients as you want. In other words, if you have multiple Crontab jobs listed within the Crontab file, then you can easily have separate MAILTO parameters for each of these jobs so that you can send the notifications about the execution of any particular job to the intended recipient. In this way, you can also save yourselves from the hassle of manually informing the concerned person about the completion of a task. View the full article