Nagios XI supports the following minimum requirements:
At least 20 GB of free hard drive space.
2 GB Memory or more.
Dual Core 2.4 GHz CPU or faster.
CentOS or RHEL (Red Hat Enterprise Linux) versions 5, 6, or 7.
MySQL, plus PostgresQL if running versions less than Nagios XI 5 or upgrading from pre-5 version.