NSClient++
A simple, powerful, and secure monitoring agent for Windows and Linux.
NSClient++ (nsclient) is the monitoring agent that runs on the machines you want to monitor. It exposes the system to your monitoring server (Nagios, Icinga, Naemon, Op5 Monitor, Checkmk, Prometheus, Zabbix-via-NRPE, …) over whichever protocol that server speaks. It can also push results, expose a REST API, scrape Windows performance counters, run external scripts, and be extended with Lua, Python, or native plugins.
- Website: https://nsclient.org
- Documentation: https://docs.nsclient.org
- Issues / discussions: https://github.com/mickem/nscp/issues
Table of contents
- Quick start
- What it does
- Supported protocols
- Common monitoring scenarios
- Extending NSClient++
- Supported platforms
- Which package to download
- Building from source
- Documentation map
- Contributing
- License
Quick start
The fastest path from zero to a working check is the Quick Start guide — it gets you installed and running your first check in about 10 minutes.
For more depth:
- Installing NSClient++ — interactive MSI walkthrough, silent install, MSI properties, remote config.
- Web interface — manage and query the agent from a browser.
- Securing NSClient++ — TLS, two-way certificate authentication, per-protocol hardening.
- How it works (concepts) — modules, commands, the filter/threshold engine shared by every check.
- FAQ — timeouts, allowed-hosts, NRPE insecure mode, performance counter pitfalls, escaping.
What it does
NSClient++ has three core jobs:
- Answer queries — let a monitoring server ask "is this machine healthy?" and return a Nagios-style status + perfdata.
- Submit results — push the same kind of results to a monitoring server on a schedule.
- Act on events — run actions (scripts, custom modules, REST calls) when something changes.
Every check shares the same filter/threshold/perf-config engine, so the same expressions work across CPU, disk, services, event logs, counters, and custom scripts. See Checks in depth.
Supported protocols
NSClient++ deliberately speaks many protocols so it can plug into whatever monitoring stack you already have.
| Protocol | Direction | Use it for | Guide |
|---|---|---|---|
| NRPE | Active (pull) | Nagios / Icinga / Naemon polling the agent — the most widely supported pattern. | Active monitoring with NRPE |
| NSCA | Passive (push) | Legacy Nagios passive submissions. | Passive monitoring (NSCA/NRDP) |
| NSCA-NG | Passive (push) | TLS-PSK successor to NSCA — modern crypto, same passive pattern. | Passive monitoring (NSCA-NG) |
| NRDP | Passive (push) | HTTP-based modern replacement for NSCA. | NRDP (in the NSCA scenario) |
| Icinga 2 API | Passive (push) | Submit scheduled check results directly to the Icinga 2 REST API. | Passive monitoring (Icinga 2) |
| Checkmk | Active (pull) | Serve a Checkmk-compatible agent dump on TCP/6556. | Checkmk agent integration |
| Prometheus | Active (scrape) | Expose OpenMetrics on /api/v2/openmetrics for Prometheus to scrape. |
Prometheus scraping |
| Graphite | Passive (push) | Stream performance data to a Graphite / Carbon backend for graphing. | GraphiteClient reference |
| Syslog | Passive (push) | Forward results as syslog records. | SyslogClient reference |
| SMTP | Passive (push) | Email notifications from check results. | SMTPClient reference |
| REST API | Active (pull) | Custom integrations, scripts, dashboards, and the built-in web UI. | REST API reference |
Common monitoring scenarios
End-to-end guides — each one has the minimal config, the command to run, and example output. Full list: docs.nsclient.org/scenarios.
System health
- Windows server health — CPU, memory, disk, uptime as a baseline
- Disk space alerting
- Service & process monitoring
- Event log monitoring
- Performance counter (PDH) monitoring
Network
- Network checks — ping, TCP port, HTTP, DNS
Extensibility
- External scripts — wrap PowerShell, batch, or VBScript checks
Extending NSClient++
NSClient++ is designed to be open-ended. Pick the extension model that fits your environment:
| Option | Best for |
|---|---|
| ExternalScripts | Reuse PowerShell, batch, shell, or any existing tooling. Simplest path. Guide |
| LuaScripts | In-process scripts with no extra runtime to install — runs anywhere NSClient++ does. |
| PythonScripts | Full Python inside the agent; great power, but you need Python installed on the host. Guide |
| Native modules | C++ plugins using the plugin API — maximum control, maximum effort. |
| Zip modules | Bundle scripts + config as a redistributable add-on. Guide |
See the Extending NSClient++ section for the full picture.
Supported platforms
- Windows: Windows 10 / 11 and Windows Server 2016 / 2019 / 2022 / 2025 on x64, x86, and ARM64. A legacy build covers Windows XP / Server 2003 through Server 2012 R2.
- Linux: Ubuntu 24.04 LTS and Rocky / RHEL / AlmaLinux 9 and 10 on x86_64 and aarch64. Other glibc-compatible distributions usually work too. Some modules are Windows-only (event log, PDH, WMI, service control).
Which package to download
The following packages are produced by the official build pipelines. Pick the one that matches your operating system and architecture:
| Operating system | Version | Architecture | Package / artifact name | Notes |
|---|---|---|---|---|
| Windows (modern) | Windows 10 / 11, Server 2016 / 2019 / 2022 / 2025 | x64 (64-bit) | NSCP-<version>-x64.msi |
Recommended for all modern Windows systems. Built with MSVC 2022. |
| Windows (modern) | Windows 10 / 11, Server 2016 / 2019 / 2022 / 2025 | x86 (32-bit) | NSCP-<version>-Win32.msi |
Use only on 32-bit Windows installations. Built with MSVC 2022. |
| Windows (modern) | Windows 11 ARM, Server 2025 ARM | ARM64 | NSCP-<version>-ARM64.msi |
Native ARM64 build, cross-compiled with the v143 toolset. Use this on Windows-on-ARM devices (e.g. Surface Pro X / Copilot+ PCs, ARM-based Azure VMs). |
| Windows (legacy) | Windows XP and above | x86 (32-bit) | NSCP-<version>-Win32-legacy-xp.msi |
Statically linked, built with the v141_xp toolset. Use this on any Windows older than Windows 10 / Server 2016. Works on x64 versions of these older OSes too. |
| Ubuntu | 24.04 LTS (Noble) | x64 (amd64) | NSCP-<version>-ubuntu-24.04-amd64.deb |
Should also install on recent Debian/Ubuntu derivatives with compatible glibc and Lua 5.4. |
| Ubuntu | 24.04 LTS (Noble) | ARM64 (aarch64) | NSCP-<version>-ubuntu-24.04-arm64.deb |
For 64-bit ARM hosts (e.g. AWS Graviton, Ampere Altra, Raspberry Pi 4/5 running Ubuntu 24.04 arm64). |
| Rocky Linux / RHEL / AlmaLinux | 9 | x64 (x86_64) | NSCP-<version>-rocky-9-x86_64.rpm |
Compatible with RHEL 9 and other RHEL 9 rebuilds (AlmaLinux 9, Oracle Linux 9, CentOS Stream 9). |
| Rocky Linux / RHEL / AlmaLinux | 9 | ARM64 (aarch64) | NSCP-<version>-rocky-9-aarch64.rpm |
64-bit ARM build for RHEL 9-family distributions. |
| Rocky Linux / RHEL / AlmaLinux | 10 | x64 (x86_64) | NSCP-<version>-rocky-10-x86_64.rpm |
Compatible with RHEL 10 and other RHEL 10 rebuilds. |
| Rocky Linux / RHEL / AlmaLinux | 10 | ARM64 (aarch64) | NSCP-<version>-rocky-10-aarch64.rpm |
64-bit ARM build for RHEL 10-family distributions. |
In addition, a stand-alone check_nsclient binary is published alongside each Linux package for use as a Nagios/Icinga check plugin.
On unsupported distributions you can build from source — see build.md.
Building from source
NSClient++ is built with CMake. On Windows it uses Visual Studio 2022; on Linux it uses GCC or Clang. See build.md for the full step-by-step build instructions, dependencies, and tips.
Documentation map
The full documentation is organised as:
- Quick Start — your first 10 minutes
- Setup — installing, web UI, hardening
- Concepts — how modules, commands, checks, permissions, and settings fit together
- Scenarios — end-to-end recipes
- Reference — every module, command, and setting
- Extending — Python, Lua, native plugins, zip modules
- REST API — programmatic access
- FAQ — operational gotchas
Contributing
Contributions are welcome — bug reports, fixes, new checks, doc improvements, and platform packaging help.
- File issues and feature requests at https://github.com/mickem/nscp/issues.
- Pull requests should target
main. CI builds Windows and Linux packages on every PR; please make sure the build is green before requesting review. - Documentation lives under
docsand is published to https://docs.nsclient.org. - For non-trivial changes, open an issue first to discuss the approach.
License
NSClient++ is dual-licensed — you may use it under either the Apache License 2.0 or the GNU General Public License, version 2.0 (only), at your option (SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-only). See COPYING for the summary, the LICENSES/ directory for the full license texts, and THIRD-PARTY-NOTICES.md for bundled third-party components.
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