To install chrootkit, SSH into server and login as root.
At command prompt type: cd /root/
At command prompt type: wget ftp://ftp.pangeia.com.br/pub/seg/pac/chkrootkit.tar.gz
At command prompt type: tar xvzf chkrootkit.tar.gz
At command prompt type: cd chkrootkit-0.44
At command prompt type: make sense
To run chkrootkit
At command prompt type: /root/chkrootkit-0.44/chkrootkit
Make sure you run it on a regular basis, perhaps including it in a cron job.