CentOS 6
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Cron's Settings
The regular jobs are controled by anacron by default on RHEL6(Scientific Linux 6 or CentOS 6 are the same). But anacron runs randomly in a day(at 3-22), so if you'd like to use cron and control jobs at a time, change like follows.
But Consider to change it if your server is virtualization environment. In virtual server, some virtual machines are running and if they executes regular jobs at a time all, the server will have many loading at a time. So it's necessary to change time on each machine by hand, or Keep anacron setting.
[root@dlp ~]#
yum -y install cronie-noanacron

# there is time settings of Cron in /etc/cron.d/dailyjobs
[2] Remove anacron settings's package, if you installed cron's setting.
[root@dlp ~]#
yum -y remove cronie-anacron