UPSMON(8) Network UPS Tools (NUT) UPSMON(8)
upsmon - UPS monitor and shutdown controller
upsmon -c command
upsmon [-D] [-p] [-u user]
upsmon is the client process that is responsible for the most important
part of UPS monitoring - shutting down the system when the power goes
out. It can call out to other helper programs for notification pur-
poses during power events.
upsmon can monitor multiple systems using a single process. Every UPS
that is defined in the upsmon.conf(5) configuration file is assigned a
power value and a type (slave or master).
-h Display the help message.
Send the command command to the existing upsmon process. Valid
fsd - shutdown all master UPSes (use with caution)
stop - stop monitoring and exit
reload - reread upsmon.conf(5) configuration file. See "reload-
ing nuances" below if this doesn’t work.
-D Raise the debugging level. upsmon will run in the foreground
and prints information on stdout about the monitoring process.
Use this multiple times for more details.
-K Test for the shutdown flag. If it exists and contains the magic
string from upsmon, then upsmon will exit with EXIT_SUCCESS.
Any other condition will make upsmon exit with EXIT_FAILURE.
You can test for a successful exit from upsmon -K in your shut-
down scripts to know when to call upsdrvctl(8) to shut down the
-p Run privileged all the time. Normally upsmon will split into
two processes. The majority of the code runs as an unprivileged
user, and only a tiny stub runs as root. This switch will dis-
able that mode, and run the old "all root all the time" system.
This is not the recommended mode, and you should not use this
unless you have a very good reason.
Set the user for the unprivileged monitoring process. This has
no effect when using -p.
The default user is set at configure time with ’configure
--with-user=...’. Typically this is ’nobody’, but other distri-
butions will probably have a specific ’nut’ user for this task.
If your notification scripts need to run as a specific user, set
You can also set this in the upsmon.conf(5) file with the
In the upsmon.conf(5), you must specify at least one UPS that will be
monitored. Use the MONITOR directive.
MONITOR system powervalue username password type
The system refers to a upsd(8) server, in the form upsname@host-
name[:port]. Some examples follow:
- "su700@mybox" means a UPS called "su700" on a system called "mybox".
This is the normal form.
- "fenton@bigbox:5678" is a UPS called "fenton" on a system called
"bigbox" which runs upsd(8) on port "5678".
The powervalue refers to how many power supplies on this system are
being driven this UPS. This is typically set to 1, but see the section
on power values below.
The username is a section in your upsd.users(5) file. Whatever pass-
word you set in that section must match the password set in this file.
The type set in that section must also match the type here - master or
slave. In general, a master process is one running on the system with
the UPS actually plugged into a serial port, and a slave is drawing
power from the UPS but can’t talk to it directly. See the section on
UPS types for more.
upsmon senses several events as it monitors each UPS. They are called
notify events as they can be used to tell the users and admins about
the change in status. See the additional NOTIFY-related sections below
for information on customizing the delivery of these messages.
ONLINE The UPS is back on line.
ONBATT The UPS is on battery.
The UPS battery is low (as determined by the driver).
FSD The UPS has been commanded into the "forced shutdown" mode.
COMMOK Communication with the UPS has been established.
Communication with the UPS was just lost.
The local system is being shut down.
The UPS needs to have its battery replaced.
NOCOMM The UPS can’t be contacted for monitoring.
In upsmon.conf(5), you can configure a program called the NOTIFYCMD
that will handle events that occur.
NOTIFYCMD "path to program"
Remember to wrap the path in "quotes" if it contains any spaces.
The program you run as your NOTIFYCMD can use the environment variables
NOTIFYTYPE and UPSNAME to know what has happened and on which UPS. It
also receives the notification message (see below) as the first (and
only) argument, so you can deliver a preformatted message too.
Note that the NOTIFYCMD will only be called for a given event when you
set the EXEC flag by using the notify flags, below:
By default, all notify events (see above) generate a global message
(wall) to all users, plus they are logged via the syslog. You can
change this with the NOTIFYFLAG directive in the configuration file:
NOTIFYFLAG notifytype flags
NOTIFYFLAG ONLINE SYSLOG
NOTIFYFLAG ONBATT SYSLOG+WALL
NOTIFYFLAG LOWBATT SYSLOG+WALL+EXEC
The flags that can be set on a given notify event are:
SYSLOG Write this message to the syslog.
WALL Send this message to all users on the system via ’wall’.
EXEC Execute the NOTIFYCMD.
IGNORE Don’t do anything. If you use this, don’t use any of the other
You can mix these flags. "SYSLOG+WALL+EXEC" does all three for a given
upsmon comes with default messages for each of the NOTIFY events.
These can be changed with the NOTIFYMSG directive.
NOTIFYMSG type "message"
NOTIFYMSG ONLINE "UPS %s is getting line power"
NOTIFYMSG ONBATT "Someone pulled the plug on %s"
The first instance of %s is replaced with the identifier of the UPS
that generated the event. These messages are used when sending walls
to the users directly from upsmon, and are also passed to the NOTIFY-
The "current overall power value" is the sum of all UPSes that are cur-
rently able to supply power to the system hosting upsmon. Any UPS that
is either on line or just on battery contributes to this number. If a
UPS is critical (on battery and low battery) or has been put into
"forced shutdown" mode, it no longer contributes.
A "power value" on a MONITOR line in the config file is the number of
power supplies that the UPS runs on the current system.
MONITOR upsname powervalue username password type
Normally, you only have one power supply, so it will be set to 1.
MONITOR myups@myhost 1 username mypassword master
On a large server with redundant power supplies, the power value for a
UPS may be greater than 1. You may also have more than one of them
MONITOR ups-alpha@myhost 2 username mypassword master
MONITOR ups-beta@myhost 2 username mypassword master
You can also set the power value for a UPS to 0 if it does not supply
any power to that system. This is generally used when you want to use
the upsmon notification features for a UPS even though it’s not actu-
ally running the system that hosts upsmon. Don’t set this to "master"
unless you really want to power this UPS off when this instance of
upsmon needs to shut down for its own reasons.
MONITOR faraway@anotherbox 0 username mypassword slave
The "minimum power value" is the number of power supplies that must be
receiving power in order to keep the computer running.
Typical PCs only have 1, so most users will leave this at the default.
If you have a server or similar system with redundant power, then this
value will usually be set higher. One that requires three power sup-
plies to be running at all times would simply set it to 3.
When the current overall power value drops below the minimum power
value, upsmon starts the shutdown sequence. This design allows you to
lose some of your power supplies in a redundant power environment with-
out bringing down the entire system while still working properly for
upsmon and upsd(8) don’t always run on the same system. When they do,
any UPSes that are directly attached to the upsmon host should be moni-
tored in "master" mode. This makes upsmon take charge of that equip-
ment, and it will wait for slaves to disconnect before shutting down
the local system. This allows the distant systems (monitoring over the
network) to shut down cleanly before upsdrvctl shutdown runs and turns
them all off.
When upsmon runs as a slave, it is relying on the distant system to
tell it about the state of the UPS. When that UPS goes critical (on
battery and low battery), it immediately invokes the local shutdown
command. This needs to happen quickly. Once it disconnects from the
distant upsd(8) server, the master upsmon will start its own shutdown
process. Your slaves must all shut down before the master turns off
the power or filesystem damage may result.
upsmon deals with slaves that get wedged, hang, or otherwise fail to
disconnect from upsd(8) in a timely manner with the HOSTSYNC timer.
During a shutdown situation, the master upsmon will give up after this
interval and it will shut down anyway. This keeps the master from sit-
ting there forever (which would endanger that host) if a slave should
break somehow. This defaults to 15 seconds.
If your master system is shutting down too quickly, set the FINALDELAY
interval to something greater than the default 15 seconds. Don’t set
this too high, or your UPS battery may run out of power before the mas-
ter upsmon process shuts down that system.
For those rare situations where the shutdown process can’t be completed
between the time that low battery is signalled and the UPS actually
powers off the load, use the upssched(8) helper program. You can use
it along with upsmon to schedule a shutdown based on the "on battery"
event. upssched can then come back to upsmon to initiate the shutdown
once it’s run on battery too long.
This can be complicated and messy, so stick to the default critical UPS
handling if you can.
REDUNDANT POWER SUPPLIES
If you have more than one power supply for redundant power, you may
also have more than one UPS feeding your computer. upsmon can handle
this. Be sure to set the UPS power values appropriately and the MIN-
SUPPLIES value high enough so that it keeps running until it really
does need to shut down.
For example, the HP NetServer LH4 by default has 3 power supplies
installed, with one bay empty. It has two power cords, one per side of
the box. This means that one power cord powers two power supply bays,
and that you can only have two UPSes supplying power.
Connect UPS "alpha" to the cord feeding two power supplies, and UPS
"beta" to the cord that feeds the third and the empty slot. Define
alpha as a powervalue of 2, and beta as a powervalue of 1. Set the
MINSUPPLIES to 2.
When alpha goes on battery, your current overall power value will stay
at 3, as it’s still supplying power. However, once it goes critical
(on battery and low battery), it will stop contributing to the current
overall power value. That means the value will be 1 (beta alone),
which is less than 2. That is insufficient to run the system, and
upsmon will invoke the shutdown sequence.
However, if beta goes critical, subtracting its contribution will take
the current overall value from 3 to 2. This is just high enough to
satisfy the minimum, so the system will continue running as before. If
beta returns later, it will be re-added and the current value will go
back to 3. This allows you to swap out UPSes, change a power configu-
ration, or whatever, as long as you maintain the minimum power value at
Besides being able to monitor multiple UPSes, upsmon can also monitor
them as different roles. If you have a system with multiple power
supplies serviced by separate UPS batteries, it’s possible to be a mas-
ter on one and a slave on the other. This usually happens when you run
out of serial ports and need to do the monitoring through another sys-
This is also complicated, especially when it comes time to power down a
UPS that has gone critical but doesn’t supply the local system. You
can do this with some scripting magic in your notify command script,
but it’s beyond the scope of this manual.
When upsmon is forced to bring down the local system, it sets the "FSD"
(forced shutdown) flag on any UPSes that it is running in master mode.
This is used to synchronize slaves in the event that a master UPS that
is otherwise OK needs to be brought down due to some pressing event on
You can manually invoke this mode on the master upsmon by starting
another copy with ’-c fsd’. This is useful when you want to initiate a
shutdown before the critical stage through some external means, such as
In the event that upsmon can’t reach upsd(8), it declares that UPS
"dead" after some interval controlled by DEADTIME in the
upsmon.conf(5). If this happens while that UPS was last known to be on
battery, it is assumed to have gone critical and no longer contributes
to the overall power value.
upsmon will alert you to a UPS that can’t be contacted for monitoring
with a "NOCOMM" notifier by default every 300 seconds. This can be
changed with the NOCOMMWARNTIME setting.
upsmon usually gives up root powers for the process that does most of
the work, including handling signals like SIGHUP to reload the configu-
ration file. This means your upsmon.conf(8) file must be readable by
the non-root account that upsmon switches to.
If you want reloads to work, upsmon must run as some user that has per-
missions to read the configuration file. I recommend making a new user
just for this purpose, as making the file readable by "nobody" (the
default user) would be a bad idea.
See the RUN_AS_USER section in upsmon.conf(8) for more on this topic.
Additionally, you can’t change the SHUTDOWNCMD or POWERDOWNFLAG defini-
tions with a reload due to the split-process model. If you change
those values, you must stop upsmon and start it back up. upsmon will
warn you in the syslog if you make changes to either of those values
during a reload.
SIMULATING POWER FAILURES
To test a synchronized shutdown without pulling the plug on your
UPS(es), you need only set the forced shutdown (FSD) flag on them. You
can do this by calling upsmon again to set the flag - i.e.:
upsmon -c fsd
After that, the master and the slaves will do their usual shutdown
sequence as if the battery had gone critical. This is much easier on
your UPS equipment, and it beats crawling under a desk to find the
upsc(8), upscmd(8), upsrw(8), upsmon(8)
upsset.cgi(8), upsstats.cgi(8), upsimage.cgi(8)
The NUT (Network UPS Tools) home page: http://www.networkupstools.org/
Wed Nov 26 2003 UPSMON(8)
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