In case neither cron.allow nor cron.deny exist in /etc/, which of the following is true?

A. Without additional configuration, no users may have user specific crontabs.
B. Without additional configuration, all users may have user specific crontabs.
C. The cron daemon will refuse to start and report missing files in the system's logfile.
D. When a user creates a user specific crontab the system administrator must approve it explicitly

題解

若「/etc/cron.allow」檔案存在,則只會接受存在於「/etc/cron.allow」檔案內的使用者操作cron。若「/etc/cron.deny」檔案存在,則只會拒絕存在於「/etc/cron.deny」檔案內的使用者操作cron。若「/etc/cron.allow」檔案和「/etc/cron.deny」檔案都存在,只會使用「/etc/cron.allow」檔案。若「/etc/cron.allow」檔案和「/etc/cron.deny」檔案都不存在,則只有root能操作cron,所以答案是選項A。