What Does 0 4 * * * Mean?
In standard 5-field UNIX / Linux Cron syntax, 0 4 * * * breaks down into five separate time units:
- Minute (0): At minute 0 (on the exact hour).
- Hour (4): At hour 4 (4:00 AM in 24-hour military time).
- Day of Month (*): Every day of the month (1 through 31).
- Month (*): Every month of the year (January through December).
- Day of Week (*): Every day of the week (Sunday through Saturday).
Combined, this expression commands the scheduler to run your task once every single day when the clock hits 04:00.
Do not confuse 0 4 * * * with 0 */4 * * *. The step expression 0 */4 * * * runs every 4 hours (6 times a day). In contrast, 0 4 * * * runs strictly once a day at 4:00 AM.