OpenNMS is the first enterprise-grade network management platform developed using the open source model. The three main functional areas of OpenNMS are service polling, which monitors services on the network and reports on their "service level"; data collection from the remote systems via SNMP in order to measure the performance of the network; and a system for event management and notifications.
ZABBIX is an enterprise-class distributed monitoring solution designed to monitor and track performance and availability of network servers, devices, and other IT resources. It supports distributed and Web-based monitoring, auto-discovery, real-time monitoring, SLA assurance, trending, and more.
pmacct is a small set of passive network monitoring tools to account, filter, classify, aggregate, and export IPv4 and IPv6 traffic. A pluggable and flexible architecture allows storing collected network data in memory tables, RDBMSs (MySQL, SQLite, PostgreSQL, BDB), and flat files, and also export via IPFIX, NetFlow, or sFlow protocols to remote collectors. pmacct features fully customizable historical data breakdown, sampling, BGP correlation, tagging, and triggers. Libpcap, ULOG, sFlow v2/v4/v5, NetFlow v1/v5/v7/v8/v9, and IPFIX are supported data capturing methods.
fwknop implements an authorization scheme called Single Packet Authorization that requires only a single encrypted packet to communicate various pieces of information, including desired access through an iptables, ipfw, or pf firewall policy and/or specific commands to execute on the target system. The main application of this program is to protect services such as SSH with an additional layer of security in order to make the exploitation of vulnerabilities much more difficult. The authorization server works by passively monitoring authorization packets via libpcap. Also supported is a robust port knocking implementation based around iptables log messages.
The sysstat package contains the sar, sadf, iostat, nfsiostat, cifsiostat, mpstat, and pidstat commands for Linux. The sar command collects and reports system activity information. The statistics reported by sar concern I/O transfer rates, paging activity, process-related activites, interrupts, network activity, memory and swap space utilization, CPU utilization, kernel activities, and TTY statistics, among others. The sadf command may be used to display data collected by sar in various formats. The iostat command reports CPU statistics and I/O statistics for tty devices and disks. The pidstat command reports statistics for Linux processes. The mpstat command reports global and per-processor statistics. The nfsiostat command reports I/O statistics for network filesystems. The cifsiostat command reports I/O statistics for CIFS filesystems.
Monit is a utility for managing and monitoring processes, programs, files, directories, and devices on a Unix system. It conducts automatic maintenance and repair and can execute meaningful causal actions in error situations. It can be used to monitor files, directories, and devices for changes, such as timestamps changes, checksum changes, or size changes. It is controlled via an easy to configure control file based on a free-format, token-oriented syntax. It logs to syslog or to its own log file and notifies users about error conditions via customizable alert messages. It can perform various TCP/IP network checks, protocol checks, and can utilize SSL for such checks. It provides an HTTP(S) interface for access.
Angel is a simple yet useful tool to monitor the services on your network. Technically speaking, it's a Perl program that runs every 'n' minutes (usually fired from your cron) and calls different perl subprograms (referred to as "plugins" from now on) to do the actual testing. It will then generate an HTML table containing the status of your network.
SNMP Monitor is a Tcl extension for monitoring static variables in routers or other agents using SNMP to access MIBs. The SNMP (Simple Network Management Protocol) uses polling or traps to communicate with the agent and the monitor equipment. MIBs are management information bases containing a wide range of interesting variables to be monitored.