We have already discussed about how to install the Rootkit Hunter in Linux operating system. Now set up email alert to you daily.

Create a shell file in cron.daily 

# vim /etc/cron.daily/rkhuntercron.sh

Add the following code:

/usr/local/bin/rkhunter --versioncheck
/usr/local/bin/rkhunter --update
/usr/local/bin/rkhunter --cronjob --report-warnings-only
) | /bin/mail -s 'rkhunter Daily Run (your server name)' emailid@email.com

Then, file permission change to be executable, 
#  chmod 755 /etc/cron.daily/rkhuntercron.sh

Finally, restart your cronjob service.
# /etc/init.d/crond restart