Additionally, cron checks each minute to see if its spool directory's
modtime (or the modtime on /etc/crontab) has changed, and if it has,
cron will then examine the modtime on all crontabs and reload those
which have changed. Thus cron need not be restarted whenever a crontab
file is modified. Note that the crontab(1) command updates the modtime
of the spool directory whenever it changes a crontab.