How are cron jobs affected when a Daylight Savings change occurs

Solution Unverified - Updated -

Environment

  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7

Issue

  • Need to verify that system cron job scripts will run as expected when Daylight Savings time moves forward and falls back

Resolution

  • cron is aware of Daylight Savings Time changes and adjusts as needed to ensure the job runs a single instance
# man 8 cron
   Daylight Saving Time and other time changes
       Local time changes of less than three hours, such as those caused by the Daylight Saving Time changes, are handled in a spe‐
       cial way.  This only applies to jobs that run at a specific time and jobs that run with a granularity greater than one hour.
       Jobs that run more frequently are scheduled normally.

       If time was adjusted one hour forward, those jobs that would have run in the interval that has  been  skipped  will  be  run
       immediately.  Conversely, if time was adjusted backward, running the same job twice is avoided.

       Time  changes  of  more than 3 hours are considered to be corrections to the clock or the timezone, and the new time is used
       immediately.

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