Monit

Monit is a small, open-source utility designed for managing and monitoring Unix systems. With its proactive approach, Monit conducts automatic maintenance, repair, and executes meaningful actions in error situations. It is particularly useful for monitoring daemon processes initiated during system boot time, like Sendmail, SSHD, Apache, and MySQL.

Monit extends its monitoring capabilities to network connections, supporting TCP, UDP, and Unix Domain Sockets, and can even test various protocols like HTTP and SMTP. Furthermore, Monit monitors general system resources on localhost, including CPU usage, memory, load average, and network interfaces.