Network UPS Tools
Power Devices support

NUT provides many features, and is always improving. Thus this list may lag behind the current code.

Features frequently appear during the development cycles, so be sure to look at the release notes and change logs to see the latest additions.

Multiple manufacturer and device support

  • Monitors many UPS, PDU, ATS, PSU and SCD models from more than 140 manufacturers with a unified interface (Hardware Compatibility List).

  • Various communication types and many protocols are supported with the same common interface:

    • serial,

    • USB,

    • network (SNMP, Eaton / MGE XML/HTTP).

Multiple architecture support

  • Cross-platform - different flavors of Unix can be managed together with a common set of tools, even crossing architectures.

  • This software has been reported to run on Linux distributions, the BSDs, Apple’s OS X, Solaris, IRIX, HP/UX, Tru64 Unix, and AIX.

  • Windows users may be able to build it directly with Cygwin. There is also a port of the client-side monitoring to Windows called WinNUT.

  • Your system will probably run it too. You just need a good C compiler and possibly some more packages to gain access to the serial ports. Other features, such as USB / SNMP / whatever, will also need extra software installed.

Layered and modular design with multiple processes

  • Three layers: drivers, server, clients.

  • Drivers run on the same host as the server, and clients communicate with the server over the network.

  • This means clients can monitor any UPS anywhere as long as there is a network path between them.

Warning Be sure to plug your network’s physical hardware (switches, hubs, routers, bridges, …) into the UPS!

Redundancy support - Hot swap/high availability power supplies

  • upsmon can handle high-end servers which receive power from multiple UPSes simultaneously.

  • upsmon won’t initiate a shutdown until the total power situation across all source UPSes becomes critical (on battery and low battery).

  • You can lose a UPS completely as long as you still have at least the minimum number of sources available. The minimum value is configurable.

Security and access control

  • Manager functions are granted with per-user granularity. The admin can have full powers, while the admin’s helper can only do specific non-destructive tasks such as a battery test.

  • The drivers, server, and monitoring client (upsmon) can all run as separate user IDs if this is desired for privilege separation.

  • Only one tiny part of one program has root powers. upsmon starts as root and forks an unprivileged process which does the actual monitoring over the network. They remain connected over a pipe. When a shutdown is necessary, a single character is sent to the privileged process. It then calls the predefined shutdown command. In any other case, the privileged process exits. This was inspired by the auth mechanism in Solar Designer’s excellent popa3d.

  • The drivers and network server may be run in a chroot jail for further security benefits. This is supported directly since version 1.4 and beyond with the chroot= configuration directive.

  • IP-based access control relies on the local firewall and TCP Wrapper.

  • SSL is available as a build option ("--with-ssl"). It encrypts sessions with upsd and can also be used to authenticate servers.

Web-based monitoring

  • Comes stock with CGI-based web interface tools for UPS monitoring and management, including graphical status displays.

  • Custom status web pages may be generated with the CGI programs, since they use templates to create the pages. This allows you to have status pages which fit the look and feel of the rest of your site.

Free software

  • That’s free beer and free speech. Licensed under the GNU General Public License version 2 or later.

  • Know your systems - all source code is available for inspection, so there are no mysteries or secrets in your critical monitoring tools.

UPS management and control

  • Writable variables may be edited on higher end equipment for local customization

  • Status monitoring can generate notifications (email/pager/SMS/…) on alert conditions

  • Alert notices may be dampened to only trigger after a condition persists. This avoids the usual pager meltdown when something happens and no delay is used.

  • Maintenance actions such as battery runtime calibration are available where supported by the UPS hardware.

  • Power statistics can be logged in custom formats for later retrieval and analysis

  • All drivers are started and stopped with one common program. Starting one is as easy as starting ten: upsdrvctl start.

  • Shutdowns and other procedures may be tested without stressing actual UPS hardware by simulating status values with the dummy-ups pseudo-driver. Anything which can happen in a driver can be replicated with dummy-ups.

Monitoring diagrams

These are the most common situations for monitoring UPS hardware. Other ways are possible, but they are mostly variants on these four.

Note these examples show serial communications for simplicity, but USB or SNMP or any other monitoring is also possible.

"Simple" configuration


One UPS, one computer. This is also known as "Standalone" configuration.

This is the configuration that most users will use. You need at least a driver, upsd, and upsmon running.

"Advanced" configuration


One UPS, multiple computers. Only one of them can actually talk to the UPS directly. That’s where the network comes in. The Master system runs the driver, upsd, and upsmon in master mode. The Slave systems only run upsmon in slave mode.

This is useful when you have a very large UPS that’s capable of running multiple systems simultaneously. There is no longer the need to buy a bunch of individual UPSes or "sharing" hardware, since this software will handle the sharing for you.

"Big Box" configuration


Some systems have multiple power supplies and cords. You typically find this on high-end servers that allow hot-swap and other fun features. In this case, you run multiple drivers (one per UPS), a single upsd, and a single upsmon (as master for both UPS 1 and UPS 2)

This software understands that some of these servers can also run with some of the supplies gone. For this reason, every UPS is assigned a "power value" - the quantity of power supplies that it feeds on a system. The total available "power value" is compared to the minimum that is required for that hardware. For example, if you have 3 power supplies and 3 UPSes, but only 2 supplies must be running at any given moment, the minimum would be 2. This means that you can safely lose any one UPS and the software will handle it properly by remaining online.

"Bizarre" configuration


You can even have a UPS that has the serial port connected to a system that it’s not feeding. Sometimes a PC will be close to a UPS that needs to be monitored, so it’s drafted to supply a serial port for the purpose. This PC may in fact be getting power from some other UPS. This is not a problem.

The first system ("mixed") is a Master for UPS 1, but is only monitoring UPS 2. The other systems are Slaves of UPS 2.

Image credits

Thanks to Eaton for providing shiny modern graphics.