Cron every hour: 0 * * * *

Pinning the minute to 0 and leaving the hour open is the canonical hourly schedule. The minute field has one matching value, the hour field has all 24, and the three date fields impose nothing, so the job runs at the top of every hour forever. @hourly is a shorthand for precisely this expression and the parser expands it to the same five fields.

The mistake worth naming is * */1 * * *. It reads as hourly to English speaking eyes, but the step of 1 in the hour field matches all 24 hours, exactly as an asterisk does, and the minute field is still open. The result is 1,440 runs a day rather than 24, discovered when the log grows sixty times faster than expected.

Minute 0 of every hour is the most contended minute on a typical machine. Log rotation, metric flushes, cache expiry and every other hourly job land there together. If the hourly job is heavy and the timing does not matter, moving it to any other minute is a one character change that often removes a visible spike.

On the day a zone leaves daylight saving time, the same wall clock hour happens twice, so an hourly schedule fires 25 times. On the day it enters, an hour disappears and it fires 23. Neither is an error, but a report that divides a daily total by 24 will be quietly wrong twice a year.