*/5 * * * * runs the job every five minutes: at minute 0, 5, 10 and so on up to 55, in every hour of every day. The slash is a step, not a division; it walks through the whole minute range from its starting point in steps of five, which gives twelve runs per hour.
What does the slash in */5 mean?
It sets a step width on a range. The star before it stands for the full range 0 to 59, and /5 picks every fifth value from its start: 0, 5, 10 … 55. The same works on an explicit range, and there the start matters: 10-20/3 hits 10, 13, 16 and 19, not 12, 15 and 18.
Is */5 the same as 0,5,10,15,20,25,30,35,40,45,50,55?
Yes, exactly the same set of minutes, and every cron implementation treats them identically. The list is worth using when the values are irregular, for example 0,7,42. For a regular rhythm the step form is shorter and easier to change later, which is why almost every real crontab uses it.
Why do steps like */7 leave an uneven gap?
Because the step restarts at the top of every hour. */7 fires at minute 0, 7, 14, 21, 28, 35, 42, 49 and 56 — and then the next run is at minute 0 again, only four minutes later. Only divisors of 60 (2, 3, 4, 5, 6, 10, 12, 15, 20, 30) give a truly even rhythm across the hour boundary.
How to add the expression
- Open the crontab with crontab -e.
- Add */5 * * * * followed by the command, using absolute paths — cron starts with a minimal PATH.
- Send output somewhere useful, for example >> /var/log/meinjob.log 2>&1, so a failing run leaves a trace.
- Check the next run times in the explainer above to confirm the rhythm you expect.