Crontab mis-entered time

Question

I have a crontab that performs a massive operation that needs to run once every five hours

#min     hour     mday     month     wday    user     command


*         */5     *         *        *      root        

/Users/pdadmin/Desktop/files.sh 1>> /Users/pdadmin/Desktop/files.log 2>&1

However, when I enter in the following, it runs once every minute! What am I doing wrong here?

Answer 1

Your crontab entry specifies that the job should run on every minute (* in the first column) of every 5th hour (*/5 in the second column). I assume you meant to run it on some specific minute of every 5th hour, i.e. once only during each eligible hour. In that case you would put, say, 0 or 42 (or really anything between 0 and 59) in the first column.

Also, the number of hours in a day is not divisible by 5, so even such an entry won't run exactly every 5 hours. It will run at hours 0, 5, 10, 15, and 20. After 20:xx it will run again at 0:xx, which is only 4 hours. Maybe this matters to you or maybe it doesn't.