Creating and managing cron jobs

Zettel#63

zettelkasten
Published

2023-04-08

How to Create a Cron Job

To create a cron job, follow these steps:

  1. Type crontab -e to open the cron table for editing
  2. Add your cron job in the following format: * * * * * command-to-be-executed
    • Each field represents a unit of time (minute, hour, day, month, and weekday)
    • Use an asterisk (*) for any field to represent every possible value
  3. Save and exit the file

Example cron job (runs every day at 3:30 PM):

30 15 * * * /path/to/script.sh

Basic Cron Commands

  • crontab -l: List all your current cron jobs
  • crontab -e: Edit your cron jobs
  • crontab -r: Remove all your cron jobs
  • crontab -ir: Interactively remove a specific cron job

Adding PATH for Cron

Cron jobs may not have access to the same environment variables as your regular user, so it’s essential to set the PATH variable. To do this, add the following line at the beginning of your crontab file:

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

Replace the example paths with the appropriate paths for your system.

Cron Tips

  1. Test your commands outside of cron first to ensure they work correctly
  2. Use absolute paths for commands and files to avoid potential issues
  3. Redirect output to a log file to capture any errors or successes. Example:
30 15 * * * /path/to/script.sh >> /path/to/logfile.log 2>&1
  1. Use the MAILTO variable to send email notifications about cron job status
  2. Be cautious when setting up frequent or resource-intensive cron jobs to avoid system overloads