monit

Monit is a small open-source utility for monitoring and managing Unix-like systems. It supervises processes, programs, files, directories, and devices, and can automatically restart services that fail or drift out of expected state. In addition to process checks, Monit can monitor resources such as CPU load, memory usage, swap, and disk space, and alert administrators when thresholds are crossed.

Monit runs as a daemon and is configured through a simple text file called monitrc. The configuration declares the items to monitor, the conditions under which actions should be taken, and the corrective actions themselves. Checks are written in a declarative language and can specify start and stop programs, restart actions, and custom scripts. It can also monitor files and directories for changes and automatically trigger alerts or actions.

A built-in web interface on port 2812 provides status and control, and Monit can send alerts via email or syslog. It supports various action types, such as starting, stopping, or restarting processes, and can execute custom scripts when a check fails or recovers. Monit can group related checks, define dependencies, and perform health checks that go beyond simple process presence.

Monit is widely used on Linux and other Unix-like systems to provide lightweight, automated service monitoring and repair. It is commonly included in many distributions' repositories and serves as a practical alternative or complement to larger monitoring suites, offering automated recovery with minimal configuration.