cronnext - Linux

Overview

cronnext is a command-line utility used to calculate the next execution time of a crontab entry. It aids in verifying crontab schedules and troubleshooting any potential issues with cron job executions.

Syntax

cronnext [-t] [-s <size>] [-d <format>] [-i <interval>] [-f <format>] expression

Options/Flags

  • -t: Use the current time as the base for calculations.
  • -s <size>: Specify the number of times to display the next execution times. Default: 5.
  • -d <format>: Set the output format to display the date and time. Default: %Y-%m-%d %H:%M:%S.
  • -i <interval>: Adjust the execution time intervals by adding the specified number of minutes, hours, days, or weeks.
  • -f <format>: Customize the output format using the strftime syntax. For example, %H:%M only shows the time, and %H:%M on %a displays the time and day of the week.

Examples

Calculating Next Execution Time:

cronnext "0 10 * * *"

Output:

2023-03-08 10:00:00
2023-03-09 10:00:00
2023-03-10 10:00:00
2023-03-11 10:00:00
2023-03-12 10:00:00

Displaying Specific Number of Executions:

cronnext -s 3 "0 10 * * *"

Output:

2023-03-08 10:00:00
2023-03-09 10:00:00
2023-03-10 10:00:00

Adjusting Execution Interval:

cronnext -i 10 "0 10 * * *"

Output:

2023-03-08 10:10:00
2023-03-09 10:10:00
2023-03-10 10:10:00
2023-03-11 10:10:00
2023-03-12 10:10:00

Customizing Output Format:

cronnext -f "%H:%M on %a" "0 10 * * *"

Output:

10:00 on Wed
10:00 on Thu
10:00 on Fri
10:00 on Sat
10:00 on Sun

Common Issues

  • Incorrect Cron Expression: Verify that the cron expression is syntactically correct and follows the required format.
  • Invalid Intervals: Ensure that the interval specified with -i is valid. Negative values or intervals that exceed the allowed limits will cause errors.
  • Time Zones: Cronnext calculations are based on the system’s default time zone. If you need to adjust for a different time zone, use the TZ environment variable.

Integration

Automating Cron Job Management:

cronnext -s 120 | xargs -I {} echo {} | mail -s "Upcoming Cron Jobs" user@example.com

This command outputs the next 120 execution times of all crontabs and emails them to the specified address, allowing for monitoring and proactive management.

Related Commands

  • crontab: Manage the system crontab entries.
  • man crontab: Display the manual page for crontab.
  • at: Schedule one-time jobs.