Crontab doesn’t remember what time you “started” (presumably the time you executed the crontab -e
or crontab filename
command).
If you want to run the job every 15 minutes starting from an arbitrary time, you’ll have to specify that time. This:
7-59/15 * * * * command
will run at 7, 22, 37, and 52 minutes after each hour. That’s assuming you’re running Vixie cron, which is the most common implementation. For better portability, you can use:
7,22,37,52 * * * * command
And remember that you can’t have spaces within any of the first 5 fields; 0, 15,30,45
, as you had in your question, is invalid.