2. Network UPS Tools Overview

2.1. Description

Network UPS Tools is a collection of programs which provide a common interface for monitoring and administering UPS, PDU and SCD hardware. It uses a layered approach to connect all of the parts.

Drivers are provided for a wide assortment of equipment. They understand the specific language of each device and map it back to a compatibility layer. This means both an expensive high end UPS, a simple "power strip" PDU, or any other power device can be handled transparently with a uniform management interface.

This information is cached by the network server upsd, which then answers queries from the clients. upsd contains a number of access control features to limit the abilities of the clients. Only authorized hosts may monitor or control your hardware if you wish. Since the notion of monitoring over the network is built into the software, you can hang many systems off one large UPS, and they will all shut down together. You can also use NUT to power on, off or cycle your data center nodes, individually or globally through PDU outlets.

Clients such as upsmon check on the status of the hardware and do things when necessary. The most important task is shutting down the operating system cleanly before the UPS runs out of power. Other programs are also provided to log information regularly, monitor status through your web browser, and more.

2.2. Installing

If you are installing these programs for the first time, go read the installation instructions to find out how to do that. This document contains more information on what all of this stuff does.

2.3. Upgrading

When upgrading from an older version, always check the upgrading notes to see what may have changed. Compatibility issues and other changes will be listed there to ease the process.

2.4. Configuring and using

Once NUT is installed, refer to the configuration notes for directions.

2.5. Documentation

This is just an overview of the software. You should read the man pages, included example configuration files, and auxiliary documentation for the parts that you intend to use.

2.6. Network Information

These programs are designed to share information over the network. In the examples below, localhost is used as the hostname. This can also be an IP address or a fully qualified domain name. You can specify a port number if your upsd process runs on another port.

In the case of the program upsc, to view the variables on the UPS called sparky on the upsd server running on the local machine, you’d do this:

/usr/local/ups/bin/upsc sparky@localhost

The default port number is 3493. You can change this with "configure --with-port" at compile-time. To make a client talk to upsd on a specific port, add it after the hostname with a colon, like this:

/usr/local/ups/bin/upsc sparky@localhost:1234

This is handy when you have a mixed environment and some of the systems are on different ports.

The general form for UPS identifiers is this:


Keep this in mind when viewing the examples below.

2.7. Manifest

This package is broken down into several categories:

  • drivers - These programs talk directly to your UPS hardware.
  • server - upsd serves data from the drivers to the network.
  • clients - They talk to upsd and do things with the status data.
  • cgi-bin - Special class of clients that you can use with your web server.
  • scripts - Contains various scripts, like the Perl and Python binding, integration bits and applications.

2.8. Drivers

These programs provide support for specific UPS models. They understand the protocols and port specifications which define status information and convert it to a form that upsd can understand.

To configure drivers, edit ups.conf. For this example, we’ll have a UPS called "sparky" that uses the apcsmart driver and is connected to /dev/ttyS1. That’s the second serial port on most Linux-based systems. The entry in ups.conf looks like this:

        driver = apcsmart
        port = /dev/ttyS1

To start and stop drivers, use upsdrvctl of upsdrvsvcctl (installed on operating systems with a service management framework supported by NUT). By default, it will start or stop every UPS in the config file:

/usr/local/ups/sbin/upsdrvctl start
/usr/local/ups/sbin/upsdrvctl stop

However, you can also just start or stop one by adding its name:

/usr/local/ups/sbin/upsdrvctl start sparky
/usr/local/ups/sbin/upsdrvctl stop sparky

On operating systems with a supported service management framework, you might wrap your NUT drivers into individual services instances with:

/usr/local/ups/sbin/upsdrvsvcctl resync

and then manage those service instances with commands like:

/usr/local/ups/sbin/upsdrvsvcctl start sparky
/usr/local/ups/sbin/upsdrvsvcctl stop sparky

To find the driver name for your device, refer to the section below called "HARDWARE SUPPORT TABLE".

Extra Settings

Some drivers may require additional settings to properly communicate with your hardware. If it doesn’t detect your UPS by default, check the driver’s man page or help (-h) to see which options are available.

For example, the usbhid-ups driver allows you to use USB serial numbers to distinguish between units via the "serial" configuration option. To use this feature, just add another line to your ups.conf section for that UPS:

        driver = usbhid-ups
        port = auto
        serial = 1234567890

Hardware Compatibility List

The Hardware Compatibility List is available in the source directory (nut-X.Y.Z/data/driver.list), and is generally distributed with packages. For example, it is available on Debian systems as:


This table is also available online.

If your driver has vanished, see the FAQ and Upgrading notes.

Generic Device Drivers

NUT provides several generic drivers that support a variety of very similar models.

  • The genericups driver supports many serial models that use the same basic principle to communicate with the computer. This is known as "contact closure", and basically involves raising or lowering signals to indicate power status.

    This type of UPS tends to be cheaper, and only provides the very simplest data about power and battery status. Advanced features like battery charge readings and such require a "smart" UPS and a driver which supports it.

    See the genericups(8) man page for more information.

  • The usbhid-ups driver attempts to communicate with USB HID Power Device Class (PDC) UPSes. These units generally implement the same basic protocol, with minor variations in the exact set of supported attributes. This driver also applies several correction factors when the UPS firmware reports values with incorrect scale factors.

    See the usbhid-ups(8) man page for more information.

  • The blazer_ser and blazer_usb drivers supports the Megatec / Q1 protocol that is used in many brands (Blazer, Energy Sistem, Fenton Technologies, Mustek and many others).

    See the blazer(8) man page for more information.

  • The snmp-ups driver handles various SNMP enabled devices, from many different manufacturers. In SNMP terms, snmp-ups is a manager, that monitors SNMP agents.

    See the snmp-ups(8) man page for more information.

  • The powerman-pdu is a bridge to the PowerMan daemon, thus handling all PowerMan supported devices. The PowerMan project supports several serial and networked PDU, along with Blade and IPMI enabled servers.

    See the powerman-pdu(8) man page for more information.

  • The apcupsd-ups driver is a bridge to the Apcupsd daemon, thus handling all Apcupsd supported devices. The Apcupsd project supports many serial, USB and networked APC UPS.

    See the apcupsd-ups(8) man page for more information.

UPS Shutdowns

upsdrvctl can also shut down (power down) all of your UPS hardware.


if you play around with this command, expect your filesystems to die. Don’t power off your computers unless they’re ready for it:

/usr/local/ups/sbin/upsdrvctl shutdown
/usr/local/ups/sbin/upsdrvctl shutdown sparky

You should read the Configuring automatic UPS shutdowns chapter to learn more about when to use this feature. If called at the wrong time, you may cause data loss by turning off a system with a filesystem mounted read-write.

Power distribution unit management

NUT also provides an advanced support for power distribution units.

You should read the NUT outlets management and PDU notes chapter to learn more about when to use this feature.

2.9. Network Server

upsd is responsible for passing data from the drivers to the client programs via the network. It should be run immediately after upsdrvctl in your system’s startup scripts.

upsd should be kept running whenever possible, as it is the only source of status information for the monitoring clients like upsmon.

2.10. Monitoring client

upsmon provides the essential feature that you expect to find in UPS monitoring software: safe shutdowns when the power fails.

In the layered scheme of NUT software, it is a client. It has this separate section in the documentation since it is so important.

You configure it by telling it about UPSes that you want to monitor in upsmon.conf. Each UPS can be defined as one of two possible types: a "primary" or "secondary".


The monitored UPS possibly supplies power to this system running upsmon, but more importantly — this system can manage the UPS (typically, this instance of upsmon runs on the same system as the upsd and driver(s)): it is capable and responsible for shutting it down when the battery is depleted (or in another approach, lingering to deplete it or to tell the UPS to reboot its load after too much time has elapsed and this system is still alive — meaning wall power returned at a "wrong" moment).

The shutdown of this (primary) system itself, as well as eventually an UPS shutdown, occurs after any secondary systems ordered to shut down first have disconnected, or a critical urgency threshold was passed.

If your UPS is plugged directly into a system’s serial or USB port, the upsmon process on that system should define its relation to that UPS as a primary. It may be more complicated for higher-end UPSes with a shared network management capability (typically via SNMP) or several serial/USB ports that can be used simultaneously, and depends on what vendors and drivers implement. Setups with several competing primaries (for redundancy) are technically possible, if each one runs its own full stack of NUT, but results can be random (currently NUT does not provide a way to coordinate several entities managing the same device).

For a typical home user, there’s one computer connected to one UPS. That means you would run on the same computer the whole NUT stack — a suitable driver, upsd, and upsmon in primary mode.


The monitored UPS may supply power to the system running upsmon (or alternatively, it may be a monitoring station with zero PSUs fed by that UPS), but more importantly, this system can’t manage the UPS — e.g. shut it down directly (through a locally running NUT driver).

Use this mode when you run multiple computers on the same UPS. Obviously, only one can be connected to the serial or USB port on a typical UPS, and that system is the primary. Everything else is a secondary.

For a typical home user, there’s one computer connected to one UPS. That means you run a driver, upsd, and upsmon in primary mode.

Additional Information

More information on configuring upsmon can be found in these places:

2.11. Clients

Clients talk to upsd over the network and do useful things with the data from the drivers. There are tools for command line access, and a few special clients which can be run through your web server as CGI programs.

For more details on specific programs, refer to their man pages.


upsc is a simple client that will display the values of variables known to upsd and your UPS drivers. It will list every variable by default, or just one if you specify an additional argument. This can be useful in shell scripts for monitoring something without writing your own network code.

upsc is a quick way to find out if your driver(s) and upsd are working together properly. Just run upsc <ups> to see what’s going on, i.e.:

morbo:~$ upsc sparky@localhost
ambient.humidity: 035.6
ambient.humidity.alarm.maximum: NO,NO
ambient.humidity.alarm.minimum: NO,NO
ambient.temperature: 25.14

If you are interested in writing a simple client that monitors upsd, the source code for upsc is a good way to learn about using the upsclient functions.

See the upsc(8) man page and NUT command and variable naming scheme for more information.


upslog will write status information from upsd to a file at set intervals. You can use this to generate graphs or reports with other programs such as gnuplot.


upsrw allows you to display and change the read/write variables in your UPS hardware. Not all devices or drivers implement this, so this may not have any effect on your system.

A driver that supports read/write variables will give results like this:

$ upsrw sparky@localhost
( many skipped )
Interval between self tests
Type: ENUM
Option: "1209600"
Option: "604800" SELECTED
Option: "0"
( more skipped )

On the other hand, one that doesn’t support them won’t print anything:

$ upsrw fenton@gearbox
( nothing )

upsrw requires administrator powers to change settings in the hardware. Refer to upsd.users(5) for information on defining users in upsd.


Some UPS hardware and drivers support the notion of an instant command - a feature such as starting a battery test, or powering off the load. You can use upscmd to list or invoke instant commands if your hardware/drivers support them.

Use the -l command to list them, like this:

$ upscmd -l sparky@localhost
Instant commands supported on UPS [sparky@localhost]:
load.on - Turn on the load immediately
test.panel.start - Start testing the UPS panel
calibrate.start - Start run time calibration
calibrate.stop - Stop run time calibration

upscmd requires administrator powers to start instant commands. To define users and passwords in upsd, see upsd.users(5).

2.12. CGI Programs

The CGI programs are clients that run through your web server. They allow you to see UPS status and perform certain administrative commands from any web browser. Javascript and cookies are not required.

These programs are not installed or compiled by default. To compile and install them, first run configure --with-cgi, then do make and make install. If you receive errors about "gd" during configure, go get it and install it before continuing.

You can get the source here:


In the event that you need libpng or zlib in order to compile gd, they can be found at these URLs:


Access Restrictions

The CGI programs use hosts.conf to see if they are allowed to talk to a host. This keeps malicious visitors from creating queries from your web server to random hosts on the Internet.

If you get error messages that say "Access to that host is not authorized", you’re probably missing an entry in your hosts.conf.


upsstats generates web pages from HTML templates, and plugs in status information in the right places. It looks like a distant relative of APC’s old Powerchute interface. You can use it to monitor several systems or just focus on one.

It also can generate IMG references to upsimage.


This is usually called by upsstats via IMG SRC tags to draw either the utility or outgoing voltage, battery charge percent, or load percent.


upsset provides several useful administration functions through a web interface. You can use upsset to kick off instant commands on your UPS hardware like running a battery test. You can also use it to change variables in your UPS that accept user-specified values.

Essentially, upsset provides the functions of upsrw and upscmd, but with a happy pointy-clicky interface.

upsset will not run until you convince it that you have secured your system. You must secure your CGI path so that random interlopers can’t run this program remotely. See the upsset.conf file. Once you have secured the directory, you can enable this program in that configuration file. It is not active by default.

2.13. Version Numbering

The version numbers work like this: if the middle number is odd, it’s a development tree, otherwise it is the stable tree.

The past stable trees were 1.0, 1.2, 1.4, 2.0, 2.2 and 2.4, with the latest stable tree designated 2.6. The development trees were 1.1, 1.3, 1.5, 2.1 and 2.3. As of the 2.4 release, there is no real development branch anymore since the code is available through a revision control system (namely Subversion) and snapshots. Since 2.7 line of releases, sources are tracked in Git revision control system, with the project ecosystem being hosted on GitHub, and improvements or other contributions merged through common pull request approach and custom NUT CI testing on multiple platforms.

Major release jumps are mostly due to large changes to the features list. There have also been a number of architectural changes which may not be noticeable to most users, but which can impact developers.

2.14. Backwards and Forwards Compatibility

The old network code spans a range from about 0.41.1 when TCP support was introduced up to the recent 1.4 series. It used variable names like STATUS, UTILITY, and LOADPCT. Many of these names go back to the earliest prototypes of this software from 1997. At that point there was no way to know that so many drivers would come along and introduce so many new variables and commands. The resulting mess grew out of control over the years.

During the 1.3 development cycle, all variables and instant commands were renamed to fit into a tree-like structure. There are major groups, like input, output and battery. Members of those groups have been arranged to make sense - input.voltage and output.voltage compliment each other. The old names were UTILITY and OUTVOLT. The benefits in this change are obvious.

The 1.4 clients can talk to either type of server, and can handle either naming scheme. 1.4 servers have a compatibility mode where they can answer queries for both names, even though the drivers are internally using the new format.

When 1.4 clients talk to 1.4 or 2.0 (or more recent) servers, they will use the new names.

Here’s a table to make it easier to visualize:

Server version

Client version

























Version 2.0, and more recent, do not contain backwards compatibility for the old protocol and variable/command names. As a result, 2.0 clients can’t talk to anything older than a 1.4 server. If you ask a 2.0 client to fetch "STATUS", it will fail. You’ll have to ask for "ups.status" instead.

Authors of separate monitoring programs should have used the 1.4 series to write support for the new variables and command names. Client software can easily support both versions as long as they like. If upsd returns ERR UNKNOWN-COMMAND to a GET request, you need to use REQ.

2.15. Support / Help / etc.

If you are in need of help, refer to the Support instructions in the user manual.

2.16. Hacking / Development Info

Additional documentation can be found in:

2.17. Acknowledgements / Contributions

The many people who have participated in creating and improving NUT are listed in the user manual acknowledgements appendix.