The folder /etc/cron.d/ is used to store all cronjobs, the cronjob is saved on the file , the format is:

minute hour day month dayofweek username command_to_run.

There might some problems – the syntax is not correct , and the result is that the whole file will be ignore.  I don’t know how to check the syntax , but i can watch to the syslog to see if there is any error. After we edit the file in crontab , the system will reload the cronjob, if there is any error it will throw an error in syslog. So i setup this before editing the cronjob file:

After i edit, wait for sometimes, if there is an error we’ll see this:

Hope it help.