Nagios setup(1) : pretty  simple and straightforward. just download nagiosxi(vmware or virtualbox image),
1. go to  download site :https://www.nagios.com/downloads/nagios-xi/vmware/，select

Workstation Pro/Player 64bit,( the file could be :nagiosxi-5.6.6-64.ova)

2. Use vmware workstation or virutalbox to import 

3. Launch this imported virtual image(the virtual machine's OS is centos)

4. After the virtual machine running. id/pw : root/nagiosxi

5. at the centos console, type :ip addr to get  its ip address(i.e. 192.168.0.32)

6. Open a browser : type : http://192.168.0.32

Click "Access Nagios Xi",  to setupo Nagios Xi, remember to input  user/pasword : nagiosadmin/passw0rd,

7. After installation successfully.  type :http://192.168.0.xx to access NagiosXi