How to Use the Command 'cronic' (with examples)

Cronic is a bash script designed to act as a wrapper for cron jobs. A common issue with these automated scripts is their tendency to frequently send emails, especially when something goes wrong or a command returns a non-zero exit status. Cronic addresses this by displaying output only if a command fails. This helps system administrators and users by reducing clutter in their email inboxes while still ensuring that they are notified if attention is needed. More detailed information about cronic can be found at this link .

Use Case 1: Call a Command and Display Its Output if It Returns a Non-zero Exit Code

Code:

cronic ls /nonexistent_directory

Motivation:

In many automated systems, such as web servers or database management systems, periodic tasks are scheduled using cron jobs. These tasks are usually intended to run without human intervention, but sometimes things can go wrong. By default, cron sends an email every time a task generates output, whether it’s an error or just a standard message. This can lead to email overload, especially if you have a lot of cron jobs running frequently. By using the cronic command, system administrators can configure cron jobs to only send emails when there really is a problem that needs attention (i.e., when an error occurs or a command exits with a non-zero status). This reduces the noise and allows for quick identification of actual issues.

Explanation:

• cronic: This is the main command that serves as a wrapper around the actual command you want to run. It manages the process of deciding when to display output.
• ls /nonexistent_directory: In this example, ls is a common Unix command used to list directory contents. The given directory, /nonexistent_directory, does not exist, so this command will return a non-zero exit code, triggering cronic to display the output.

Example Output:

ls: cannot access '/nonexistent_directory': No such file or directory

In this example, because the directory does not exist, the ls command fails and returns a non-zero exit code. Cronic captures this error and displays the message, informing the user of the issue.

Conclusion:

In summary, cronic is a highly useful tool for managing cron jobs by ensuring that only necessary output is displayed, thereby mitigating the problem of email overload caused by non-essential stdout messages. It is particularly valuable in cases where cron jobs are set to run frequently, and reducing noise in alert systems is a priority. By wrapping your commands using cronic, you enhance your system’s monitoring without increasing the superficial communication load.