On CentOs it is easy to realize this. By default the yum update daemon is running, but make sure it is by executing the setup command and making sure that the yum-updatesd system service is running. The yum daemon its settings are found in /etc/yum, all you need to do is to edit the config file.
If you want a daily update with logging to /var/log/yum.log then you could copy the following settings.
# how often to check for new updates (in seconds)
run_interval = 86400
# how often to allow checking on request (in seconds)
updaterefresh = 600
# how to send notifications (valid: dbus, email, syslog)
emit_via = syslog
# should we listen via dbus to give out update information/check for
# new updates
dbus_listener = no
# automatically install updates
do_update = yes
# automatically download updates
do_download = yes
# automatically download deps of updates
do_download_deps = yes
That's it! Make sure to check if it is working properly by checking the log file after 24 hours.