Вообще cron в #Linux - это довольно топорная и плохо продуманная хрень.

Невозможно написать выражение "каждые 40 минут". Это как вообще? Чем думал автор?

Ещё видел, как девопсу-стажеру дали задачу сделать запуск кроном "каждые 25 минут". И угорали потом с него.

@nonsense

А это не оно?

Crontab every hour
This is most commonly used for running cron every hour and executing a command after an interval of one hour.
crontab format every hour is simple to have hour field as * which runs every hour as the clock switches to new hour. if you want to run it at the beginning of hour the minute filed needs to be 0 or any other minutes when you want to run it at a specific minute of the hour.
cron every hour to run at the beginning of the hour.00 * * * * rm /home/someuser/tmp/*

cron every hour to run at 15 minute of an hour..

15 * * * * rm /home/someuser/tmp/*
cron every minute

To run cron every minute keep the minutes field as * , as minute changes to new minute cron will be executed every minute. if you want to run it continuously every hour then the hour field also needs to have value of * .

* * * * * rm /home/someuser/tmp/*

if you want to run a script every minute at specific hour, change the value of hour field to specific value such as 11th hour.

* 11 * * * rm /home/someuser/tmp/*