Nagios is a free and open source computer software application that monitors systems, networks and infrastructure. Nagios offers monitoring and alerting services for servers, switches, applications and services. It alerts users when things go wrong and alerts them a second time when the problem has been resolved.
Monitoring of network services such as SMTP, POP2, HTTP, NNTP, ICMP, SNMP, FTP, SSH.
Monitoring of host resources such as processor load, disk usage, system log on a majority of network operating systems, including Microsoft Windows, using monitoring agents.
Monitoring of any hardware like probes for temperature, alarms,etc. which have the ability to send collected data via a network to specifically written plugins.
Remote monitoring using Nagios Remote Plugin Executor or through SSH or SSL encrypted tunnels.
Parallelized service checks and automatic log file rotation.
Support for implementing redundant monitoring hosts, performance data graphing and database backend.
A web-interface for viewing current network status, notifications, problem history, log files, etc.
NRPE — Nagios Remote Plugin Executor
NRDP — Nagios Remote Data Processor
NSClient++ — (program used to monitor Windows machines)
NCPA — Nagios cross Platform Agent