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Linux system administrators and developers often use cron commands to perform periodic tasks. However, there is another powerful tool for scheduling of one-time tasks, which is at command. This article will dive into at command, including its syntax, usage examples, and best practices.

Understand at command

at command is a versatile utility that allows users to schedule commands or scripts to be executed at specific times in the future. It is especially suitable for running one-time jobs such as maintenance tasks, backups, or system updates without manual intervention. at command reads the commands to be executed from standard input or file and arranges them accordingly.

Install at command

Most Linux distributions have the at command pre-installed. However, if you don't have it on your system, you can install it using the distribution's package manager. For Debian-based distributions, use the following command:

 sudo apt-get install at

For Red Hat-based distributions, use the following command:

 sudo yum install at

Syntax and options

The basic syntax of at command is as follows:

 at [OPTIONS] TIME

The options available to at command include:

• -f : Specifies the file containing the command to be executed.
• -t : Use Unix timestamp to specify the time to run the command.
• -m : Send an email to the user after the job is completed.
• -q : Specifies the queue to which jobs are to be placed.

Arrange one-time homework

To schedule a one-time job, just provide the required execution time. at command supports various time formats, such as:

• Relative time: "now 1 hour" or "now 30 minutes"
• Absolute time: "2:30 PM" or "15:30"
• Date and time: "10:00 AM tomorrow" or "2025-08-04 18:00"

For example, to schedule a one-time job and create a file containing "Hello, World!" in the /tmp directory one hour later, you can use the following command:

 echo "echo 'Hello, World!' > /tmp/hello_world.txt" | at now 1 hour

Alternatively, you can arrange the command as follows:

 at now 1 hour  /tmp/hello_world.txt'

Press CTRL D to exit at command terminal.

List and manage scheduled jobs

To list all scheduled jobs for the current user, use the "atq" command:

 atq

To delete scheduled jobs, use the "atrm" command followed by the job ID:

 atrm<job_id></job_id>

Best Practices

Keep the following best practices in mind when using at command:

• Always verify that at command is installed and enabled on your system.
• Use descriptive comments in your at jobs to make it easier to understand its purpose.
• Test commands or scripts before using the at command to schedule them.
• Remember that at command is designed for one-time jobs. For repetitive tasks, use the cron command.

at command example

Here are some examples of how to use at command:

1. Schedule tasks at 10:00 AM: at 10:00 AM
2. Schedule tasks at 10:00 am on July 25: at 10:00 AM July 25
3. Schedule tasks at 10:00 am on June 22, 2023: at 10:00 AM 6/22/2023
4. Schedule tasks at 10:00 am on the same day next month: at 10:00 AM next month
5. Schedule tasks at 10:00 am tomorrow: at 10:00 AM tomorrow
6. Schedule the task to be executed after one hour: at now 1 hour
7. Schedule the task to be executed after 30 minutes: at now 30 minutes
8. Schedule tasks to be performed one and two weeks later: at now 1 week; at now 2 weeks
9. Schedule tasks to be performed one year and two years later: at now 1 year; at now 2 years
10. Schedule tasks to execute at midnight (12:00 AM): at midnight

Advanced Tips

1. Schedule multiple commands: execute multiple commands in a job sequentially, and you can enter one command per line in the at command terminal. After entering all commands, press CTRL D to exit and save the job.

2. Use script: Create a shell script that contains all the commands to be run and specify the script file using the -f option. Make sure the script is executable.

3. Receive email notifications: Use the -m option to receive email notifications after the job is completed.

4. Specify queue: The at command allows you to specify the queue to put the job into using the -q option (sequential letters). Jobs in different queues are independent of each other.

at command is a powerful tool, but it is not the only option to schedule tasks in Linux. For repetitive tasks or more complex scheduling needs, consider using a cron system, which provides additional flexibility and control over task scheduling.

Remember, the at command is suitable for one-time tasks, and the cron command is suitable for periodic tasks. With these tips, you can take advantage of at commands, automate workflows, and increase productivity. I wish you a happy dispatch!

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