These are the list of Open source monitoring software for system administrators.
1. Nagios Core
Nagios Core is open source with multiple APIs for extending core functionality,it can serves as event scheduler, event processor, and also as alert manager. It is very easy to implement and was natively designed to run on Linux systems
2. Ganglia
Ganglia is a monitoring software for high performance computing system and server clusters, it can used to view CPU load averages statistics or network utilization statistics for many server nodes.
Ganglia software is bundled with enterprise-level Linux distributions such as Red Hat Enterprise Level (RHEL) or the CentOS repackaging of the same.
3. Graphite.
Graphite is an enterprise-ready monitoring tool that runs equally well on cheap hardware or Cloud infrastructure. Teams use Graphite to track the performance of their websites, applications, business services, and networked servers. It marked the start of a new generation of monitoring tools, making it easier than ever to store, retrieve, share, and visualize time-series data.
Graphite requires a UNIX-like Operating System and Python 2.7 or greater, however, not Python 3, detail requirement can be found at http://graphite.readthedocs.io/en/latest/install.html. although, most of the current Linux distributions have all of the requirements included in the base packages. CentOS and RHEL distributions may require the EPEL repository to be installed.
4. PRTG
PRTG can scan network segments by pinging defined IP ranges. This way PRTG will automatically recognize a wide range of devices and systems and create sensors from predefined device templates. This saves you a lot of configuration work and you can start monitoring right away.
5. Site24
Site24x7 offers a centralized approach to monitor your virtual infrastructure, on-premises IT environment, and cloud infrastructure–all on a single platform.
Monitor usage and performance for key PaaS services running in your Amazon Web Service environment.
Get a comprehesive view into the health of your EC2 server instances.
Monitor resource utilization and operational health of 100+ Azure services.
Analyze virtual machine workloads and host resource utilization on your vSphere environment.
Check status of your Docker containers.