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atrun Command in Linux
atrun is a part of the at command utility on Linux that allows you to process the at job queue. Unlike at command, the atrun is not a standalone utility, instead, it is a script that runs as a cron job to process the at job queue on your Linux system. The atrun is responsible for executing commands that you scheduled using the at command on your Linux system.
When you create a job using the at command, it adds the jobs to the at scheduled jobs queue. The atrun command periodically checks this queue and executes the scheduled commands based on their specified time frame. With atrun command, you can scan your job queues, identify pending jobs, and execute the jobs at their specified times.
Table of Contents
- Syntax of atrun Command in Linux
- Examples of atrun Command in Linux
- Configuration and Directories for atrun
Syntax of atrun Command in Linux
The basic syntax to execute the atrun command on Linux is given below −
atrun [-l load_avg] [-d]
The -l option in the above syntax allows you to set a threshold for system load, above which the scheduled jobs won’t be executed on the system. By default, this threshold is set to 1.5 times the number of CPUs that are currently active. The -d option is used for debugging purposes and when you enable it, the error messages are sent to standard error output instead of being handled in the usual manner.
The atrun command executes tasks that have been scheduled using the at command. It’s essentially a shell script that triggers the /usr/sbin/atd service when used with the -s flag. This setup is mainly to ensure compatibility with systems that were set up using older standards.
Examples of atrun Command on Linux
The atrun command is not directly used by the users, as it is a part of the at jobs scheduling mechanism. It is executed by the at daemon called atd which is responsible for executing jobs on the system. The following are a few examples related to at command that involve atrun indirectly −
- Schedule a Job for a Specific Time
- Remove a Scheduled Job
Schedule a Job for a Specific Time
Let’s consider the first example that creates an at job of printing a Hello message right after the 1 minute of the current time −
echo "echo 'Hello, Linux Users'" | at now + 1 minute
In this example, the atrun will execute this job at the specified time.
Remove a Scheduled Job
Let’s consider another example where a specified job is deleted using the atrm command followed by the job number you want to delete −
atrm [job number]
Once you execute the atrm command with a specified job number, the atrun will no longer execute this job on your system.
Note − For the atrun command to function properly, it requires the cron daemon to be active and set to execute atrun at regular intervals.
Configuration and Directories for atrun
The files are directories are integral part of any command to ensure it functions properly on the system. The following are some configurations and directories of atrun command on Linux systems −
| Configuration & Directories | Description |
|---|---|
| /etc/pam.d/atrun | This is a PAM configuration file for the atrun command that defines authentication requirements and other security policies. |
| /var/at/jobs | It is a jobs directory that holds the actual job files for tasks scheduled with the at command. Here, in this directory, each file represents a separate job and contains the script or commands that will be executed. |
| /var/at/spool | It is a directory that stores output spool files. Once the atrun executes a job, the output generated by that job is stored here, unless it is redirected elsewhere by the job script. |
Conclusion
atrun is a critical component of at command line utility that facilitates the execution of scheduled tasks on your system. This guide has provided insights into the syntax and usage of the atrun command, alongside examples that illustrate its application within the Linux environment.
Additionally, atrun also provides you with information about the configuration file and directories related to atrun. It will help you offer a comprehensive understanding of its operational framework.