crontab - scheduling a job to run 6 min on hr and then every 15 mins

Question

I am trying to schedule a job which starts 6 mins past the hr every hr and then runs every 15 mins. So it kicks off at 10:06 then 10:21, 10:36,10:51. I know one way is : 06,21,36,51 * * * * /bin/foo

However why doesn't something like this work: 06/15 * * * *

Answer 1

You actually want it separeted by comma with no space between it, so it takes place in all the minutes you want:

6,21,36,51 * * * * /bin/foo

or you could use it every 15 minutes which would look like this:

6-59/15 * * * * /bin/foo

For more information you can man crontab 5 or check this url http://www.manpagez.com/man/5/crontab/

The 6/15 doesnt work because it doesnt know how to divide it, if you had it like 0-59/15 it could work but then it would not count the initial 6 that you wish for.

The initial number should be a range that will be divided by the number after the / to run every X minutes (where X is the number that comes after the /) within the range you gave it.

another example would be 0-40/5 which would run every 5 minutes until the 40 minutes.