Monit

Monit is a free, open-source utility for monitoring and managing Unix systems, with the ability to repair failed services automatically. It is best suited to administrators running self-hosted Linux or macOS machines and containers. The combination of service checks, corrective actions, alerts, and a control interface makes it a strong lightweight supervisor, provided root access and community-based support fit your operation.

Overview

Monit watches local daemon processes and can restart a process that stops or stop one consuming excessive resources. It also checks files, directories, and filesystems for timestamp, checksum, or size changes, so it can detect configuration drift, unexpected edits, or storage conditions rather than merely reporting that a service is down.

Network checks cover TCP, UDP, and Unix domain sockets, with built-in protocol tests including HTTP and SMTP. Scheduled programs or scripts can be evaluated by their exit value, triggering an action or an alert. This breadth suits a small host where one utility must supervise services, files, endpoints, and routine checks without a separate monitoring stack.

Monit integrates with init, upstart, and systemd and can use existing run-level scripts. In a container it can run as PID 1, combining init responsibilities with service monitoring in one lightweight package. The maker says it uses OpenSSL 3.5.7 statically linked and PAM support dynamically linked.

Key features

Automated service care

Process rules can turn a stopped daemon into an automatic restart, or stop a resource-hungry process before it affects the host further. This is valuable for unattended servers, but corrective rules need careful thresholds: an aggressive policy can repeatedly restart or terminate a service instead of solving its underlying fault.

Checks, metrics, and alerts

Monit monitors CPU, memory, system load, and network interfaces alongside its process, filesystem, socket, and script checks. Customizable messages describe error conditions, with logging to syslog or Monit's own log file. It can therefore support both immediate notification and post-event diagnosis, although it is oriented toward host and service supervision rather than a broad analytics platform.

Web control

The built-in HTTP(S) interface shows monitored-service status and lets an operator start, stop, or restart processes and enable or disable monitoring. That direct control is practical during maintenance, while the self-hosted design leaves deployment, access control, and ongoing administration to the user.

Pricing

Monit costs nothing. It is free open-source software under the GNU Affero General Public License (AGPL), with no paid tiers or subscription renewal to budget for. That makes it suitable for individual administrators and organizations that can operate their own Unix monitoring without a commercial support contract.

The trade-off is operational responsibility: deployment and maintenance are self-hosted, and the maker directs questions to a community mailing list rather than answering support requests sent directly to the company. Process I/O activity metrics normally require Monit to run as root, an important permission and security consideration when deciding how to deploy it.

Platforms

Monit runs on Linux and macOS, with multiple-OS coverage within the Unix-oriented platforms listed. It supports self-hosted deployments, VM monitoring, service monitoring, and agentless monitoring. Windows is not among its supported platforms, so mixed Windows estates need another tool or a separate monitoring layer.

Who it's for

Choose Monit for a self-managed Unix server, virtual machine, or container where service recovery matters as much as status reporting. It fits administrators who want existing init or systemd arrangements, script-based checks, protocol probes, and alerts in one package, and container operators who want PID 1 duties combined with supervision.

Look elsewhere if you need Windows coverage, a hosted control plane, or process I/O metrics without granting root privileges. Teams that require vendor-backed support should also account for the community mailing-list model.

Pros and cons

Pros

• Repairs as well as detects: failed processes can be restarted and over-consuming ones stopped.
• Wide check types: files, filesystems, scripts, sockets, network protocols, and system resources can all drive actions or alerts.
• Flexible service integration: init, upstart, systemd, and existing run-level scripts are supported.
• Container-ready: running as PID 1 can combine initialization and monitoring in a lightweight deployment.
• Zero license cost: the AGPL-licensed software has a free plan.

Cons

• Unix-focused: Linux and macOS support does not cover Windows hosts.
• Root may be required: process I/O metrics normally need root execution.
• Self-hosted operations: you manage deployment, access, and upkeep yourself.
• Community support route: the maker points questions to a mailing list and does not provide direct company support for support requests.

Alternatives

Glances is another free, open-source system monitor, with Linux, macOS, Windows, Android, web, API, and self-hosted options; choose it when cross-platform visibility matters more than Monit's automated repair focus. PM2 offers a free Runtime plan with a real-time web interface and a Plus plan at $79 a month, making it a better fit when process management and optional paid monitoring align with your deployment.

Process Lasso targets Windows and has freemium plans, including $4.95 a month for one PC or $24.95 a year, so it suits Windows users instead. bottom (btm) is a free Linux, macOS, and Windows monitor for readers seeking a multi-platform monitor without stated commercial limits.

OpenProcMon is free, MIT-licensed, 64-bit Windows-only software whose live capture requires Administrator privileges. runit is free service supervision for Linux, macOS, and self-hosted deployments, with no commercial limits stated. Ambih Monitor has a free tier with five-session history per project and a Pro tier at $10 a month billed annually, for Windows users wanting session history and anomaly detection. AppControl is free Windows software with no email or registration required and optional premium features potentially added later.

For broader discovery, see Process Monitoring Software and Infrastructure Monitoring.

Verdict

Monit is a strong choice for administrators who want free, self-hosted Unix service monitoring that can take corrective action instead of merely raising alarms. Its main reasons to look elsewhere are Windows requirements, root-dependent process I/O metrics, or the need for hosted operations and direct vendor support.