An open-source computer-software application, 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.
Nagios was originally designed to run under Linux, but it also runs well on other Unix variants. It is free software licensed under the terms of the GNU General Public License version 2 as published by the Free Software Foundation.
Monitoring of network services (SMTP, POP3, HTTP, NNTP, ICMP, SNMP, FTP, SSH)
Monitoring of host resources (processor load, disk usage, system logs) on a majority of network operating systems, including Microsoft Windows with the NSClient++ plugin or Check MK.
Monitoring of anything else like probes (temperature, alarms,etc.) which have the ability to send collected data via a network to specifically written plugins
Monitoring via remotely run scripts via Nagios Remote Plugin Executor
Remote monitoring supported through SSH or SSL encrypted tunnels.
A simple plugin design that allows users to easily develop their own service checks depending on needs, by using their tools of choice (shell scripts, C++, Perl, Ruby, Python, PHP, C#, etc.)
Available data graphing plugins
Parallelized service checks
The ability to define network host using ‘parent’ hosts, allowing the detection of and distinction between hosts that are down or unreachable
Contact notifications when service or host problems occur and get resolved (via e-mail, pager, SMS, or any user-defined method through plugin system)
The ability to define event handlers to be run during service or host events for proactive problem resolution
Automatic log file rotation
Support for implementing redundant monitoring hosts
An optional web-interface for viewing current network status, notifications, problem history, log files, etc.
Data storage via text files rather than database
Nagios Remote Plugin Executor (NRPE) is a Nagios agent that allows remote system monitoring using scripts that are hosted on the remote systems. It allows for monitoring of resources such as disk usage, system load or the number of users currently logged in. Nagios periodically polls the agent on remote system using the check_nrpe plugin.
Nagios Remote Data Processor (NRDP) is a Nagios agent with a flexible data transport mechanism and processor. It is designed with an architecture that allows it to be easily extended and customized. NRDP uses standard ports and protocols (HTTP(S) and XML) and can be implemented as a replacement for NSCA.
This program is mainly used to monitor Windows machines. Being installed on a remote system NSClient++ listens to port TCP 12489. Nagios plugin that is used to collect information from this addon is called check_nt. As NRPE, NSClient++ allows to monitor the so-called ‘private services’ (memory usage, CPU load, disk usage, running processes, etc.) Nagios is a host and service monitor which is designed to inform your network problems.