Crontab

1) #> nano /var/spool/cron/root
Then type in the cron entry and save it
#> service crond restart
It cannot work if have not restart crond

2) #> crontab -e
Then type in the cron entry and save it

3) #> nano /etc/crontab
type in the cron entry and save it

I can use above three method without any problem.

However I cannot use crontab [filepath] method

4) #> crontab /home/admin/domain.com/www/testing/crontab.dat
*crontab.dat is a cron entry.
after type in this line,
I use crontab -l and see cron entry has been added to /var/spool/cron/root
However, the cron job will not run even I restart crond.