Smart Power Monitoring with Network UPS Tools
By Nathan Willis - November 13, 2009
An uninterruptible power supply (UPS) is a must-have in server
 environments, and for many desktop users as well. But although simply
 connecting your PC or server to a UPS will protect you from intermittent
 power outages and give you the chance to shut the system down at the
 keyboard, an unattended power outage could still cause problems. For added
 protection, you can run a power-monitoring utility that will read status
 information from the UPS and perform a clean shutdown of the connected
 machine (or machines), preserving data and stopping processes in the
 proper state.



NUT Basics
The premiere UPS monitoring tool on Linux is Network UPS Tools (NUT), a
 free software tool that supports hundreds of UPS models from a wide range
 of vendors. NUT can monitor UPSes connected via serial cable or USB, and
 is designed for networked operation to control multiple servers and
 workstations.

Since the vast majority of UPSes include only one USB or serial connection,
 NUT can be configured to run in “slave” mode, listening on a TCP port
 for a shutdown notice from the directly-connected computer. That way, you
 can connect your primary server to the UPS with the cable in “master”
 mode, but ensure that other devices — such as a workstation, firewall,
 or NAS box — receive the message that power is out and shut down
 cleanly. You can even configure NUT to shut down the slave devices
 immediately, preserving more battery power for the master, in case power
 is restored.

NUT consists of three main pieces: the drivers that interface with the
 actual UPS hardware, decoding its status and reports to determine whether
 power is present and how much battery charge remains, the upsmon client
 that monitors UPS status and responds to power events by logging, sending
 notification messages, and shutting down the system when needed, and the
 upsd daemon that passes information between upsmon and the various
 drivers. This separation of duties is what allows NUT to work in a
 networked environment; a slave machine can run only upsmon and listen for
 power outage events from the master, and the master can connect to
 multiple hardware UPSes, as is the case for servers with redundant power
 supplies.


Setup and Basic Monitoring
You can download NUT source code and binaries from the project’s Web
 site, but most Linux distributions include it through their package
 management systems. The newest release is version 2.4, from January of
 2009. As of the moment, the online documentation has not caught up to the
 changes since the last release (2.2), but the documentation and
 configuration help included in the packages is enough to go by.

To configure your system, first check the model names and numbers of the
 UPSes you wish to monitor. NUT installs a current list sorted by
 manufacturer to /usr/share/nut/driver.list; consult the list and note the
 name of the driver required for your UPS. Many USB-connected models are
 supported by the same driver, usbhid-ups, so it will appear in the
 examples that follow. Serial port models generally use a specific driver.

Next you will need to set up up to five configuration files (depending on
 how you use NUT): nut.conf, ups.conf, upsd.conf, upsd.users, and
 upsmon.conf. All reside in /etc/nut/. nut.conf contains only one entry,
 the mode in which you want to run NUT. The choices are standalone,
 netserver, and netclient. Use netclient on slave machines, and the only
 other file you need to configure is upsmon.conf. Standalone mode is for
 basic, single-machine usage; netserver adds the ability to send messages
 over the network to slave machines.

In ups.conf, you add an entry for each UPS physically connected to the
 machine — only one for basic usage, but redundant, server setups could
 contain multiple entries. A typical entry in ups.conf looks like this:
	[primaryups]
driver = usbhid-ups
port = auto
desc = "My main server"

The name in brackets is entirely your choice; it should be descriptive if
 you have more than one UPS, as it will appear in the logs and in NUT’s
 system messages. The “driver” property lists which hardware driver NUT
 should use to communicate with the UPS — the same driver you looked up
 earlier in /usr/share/nut/driver.list. The “port” property tells NUT
 where the UPS is connected; for USB-connected UPSes, use auto;
 serial-connected UPSes would use /dev/ttyS0, /dev/ttyS1, or so on. The
 “desc” property is solely to record further detail about the UPS to
 aid your memory.

In upsd.conf, the most important setting is the LISTEN directive; it
 specifies the IP addresses (and optionally, ports) on which NUT will
 respond to messages. For a standalone setup, use LISTEN 127.0.0.1. For a
 netserver master, you should also add an entry for the computer’s public
 IP address, such as LISTEN 192.168.2.10. You can specify the port after
 the IP address if you desire; the default is 3493.

The upsd.users file allows you to configure “NUT users” that upsmon
 uses to connect; not simply using the system’s real Unix accounts
 provides a layer of increased security. This can be as simple as:
	[myupsuser]
password = thepassw0rd
upsmon master

…for a basic upsmon account on the master machine. An account for slave
 machines should specify upsmon slave instead. More complex setups allow
 you to grant specific privileges to different user accounts; the comments
 in the sample upsd.users file explain the options.

Finally, upsmon.conf configures the behavior of upsmon, the program that
 will actually monitor the UPS status of either the physical machine or a
 remote master. There are a lot of options allowing you to change the
 status polling frequency, log messages, and other details, but to get
 started the only line you need to add is a MONITOR directive, specifying
 the UPS, server, and NUT username/password. For example, MONITOR
 primaryups@bigserver 1 myupsuser thepassw0rd master indicates monitoring
 of the UPS example specified in the example file configurations above.

“Bigserver” is the hostname of the machine, “1” is the number of
 power supplies controlled by this server (1 is the default, and is
 unlikely to need changing unless you deal with redundant setups), and
 “master” indicates that this is the NUT master. A slave machine, such
 as a second PC attached to the same UPS but not connected to the USB
 monitoring cable, would specify MONITOR primaryups@bigserver 1 myupsuser
 thepassw0rd slave. Once configuration is complete, you can start the
 system with /etc/init.d/nut start.

With this configuration, upsd will monitor the UPS, and upsmon will look
 for power events. Should building power fail, upsmon will log the event
 and send a “We are shutting down soon” message to all logged-in users.
 When the battery power gets low, the upsmon process running on the master
 relays a shutdown command to the upsmon processes on the slaves. The slave
 machines will shut down gracefully, ensuring that disk partitions and RAID
 arrays are not left in an unstable state, lock files strewn about
 heedlessly, or any of the other nastiness associated with a sudden power
 outage. Last but not least, after the slave machines have shut down, the
 master shuts itself down.



PowerChute, Apcupsd, and Other Options
Admittedly, for basic use, NUT requires quite a few configuration steps.
 Fortunately, as we have seen, none of them are arduous in length or
 particularly arcane in syntax. The benefit is the flexibility to support
 an wide variety of hardware products and complex configurations, something
 other UPS monitoring options cannot do.

For example, there is a package called upsd unrelated to the NUT daemon of
 the same name. This upsd can monitor just one UPS attached directly to the
 host computer, and is limited in its hardware support to devices made by
 Powercom. However, if you use a Powercom UPS and do not need the
 networking or redundancy functions of NUT, you should take a look; this
 upsd’s simplicity and ease-of-use may fit the bill.

Similarly, OpenUPSd is limited in scope to certain kinds of
 serial-connected Belkin UPSes — those that share a single communications
 protocol called “regulator pro.” On the other hand, OpenUPSd does
 support networking, and the author reports that he is adding support for
 American Power Conversion (APC) UPS models, making the project one to
 watch.

Finally, APC provides a proprietary UPS monitoring tool called PowerChute
 with many of its UPSes. PowerChute is a Java-based program, and is
 naturally limited to APC hardware. More interesting is Apcupsd, a
 GPL-licensed replacement. Apcupsd offers many of the same features as NUT,
 including networking, though of course only for APC devices. It is
 configured through a single file, apcupsd.conf, making it potentially
 easier to maintain and troubleshoot than NUT.

For example, a sample configuration for a networked server would contain
 just:
	UPSCABLE usb
UPSTYPE usb
DEVICE
LOCKFILE /var/lock
UPSCLASS standalone
UPSMODE disable
NETSERVER on

Corresponding slave machines would use an apcupsd.conf file like this:
	
UPSCABLE ether
UPSTYPE net
LOCKFILE /var/lock
DEVICE 192.168.2.10:3551
UPSCLASS standalone
UPSMODE disable
POLLTIME 10

…in order to connect to the master running at IP address 192.168.2.10.

Whichever solution you use, though, you benefit through the increased
 reliability of a “smart” power management system. Simply shutting down
 your machine cleanly during a blackout can prevent stability problems the
 next time you start up, and the odds are against the blackout striking
 during business hours when you are at the keyboard. Advanced features in
 both NUT and Apcupsd can do more, like manage multiple UPSes on servers,
 or (with proper BIOS support) automatically restart computers after a
 blackout is over and power has been restored.

That’s smart power, indeed