ifndef::external_title[]
NUT Frequently Asked Questions
==============================
endif::external_title[]

== I just upgraded, and ...
You have read link:UPGRADING.adoc[UPGRADING] in the base directory of the
distribution, right?

If not, go read it now, then come back to this file if your
question wasn't answered in there.

== My UPS driver now says it's 'broken', and won't start.  What now?
Or a variation like...

== My favorite UPS driver disappeared after an upgrade.  What now?

Drivers are occasionally removed from the tree if they are no longer
receiving maintenance, or sometimes renamed to better reflect their
hardware support scope or replaced by a more generic driver.
There have been several architectural changes to the driver code
in recent times, and drivers which were not converted by someone
are eventually dropped.

This is called progress.  We do this in order to avoid a situation
where someone believes that a driver is being maintained when it is
actually rotting slowly in the tree.  It also keeps the tree free of
old compatibility hacks for code that nobody actually uses anyway.

To get a driver back into current releases, you need to convert it
yourself or get someone to do it for you.  This is not difficult.
The hardest part of any driver is decoding the protocol, and that's
already been done in the old version.

== My UPS driver program won't work.  I'm starting it as root, and root owns the device, so what's the problem?

*Answer 1*

The drivers drop root privileges long before the serial or USB port is
opened.  You'll need to change the permissions on that port so that
their new user id can access it.  Normally this is 'nobody', but it
may be changed at compile-time by using `configure --with-user` or
in the `ups.conf` file for driver settings with `user=...`.

Read the error message.  If you have a permissions mismatch, then
you'll see something like this:

	Network UPS Tools - APC Smart protocol driver 0.60 (1.1.7)
	This program is currently running as youruid (UID 1234)
	/dev/ttyS2 is owned by user root (UID 0), mode 0600
	Change the port name, or fix the permissions or ownership
	of /dev/ttyS2 and try again.
	Unable to open /dev/ttyS2: Permission denied

Now is a good time to point out that using 'nobody' is a bad idea,
since it's a hack for NFS access.  You should create a new role
account (perhaps called 'ups' or 'nut'), and use that instead.

Also, scroll down to the "security domains" question to see an
even better way of restricting privileged operations.  Neither the
drivers nor `upsd` ever need 'root' powers, and that answer tells you
how to make it work.

*Answer 2*

You can also specify a user with `user=` in the global part of
linkman:ups.conf[5].  Just define it before any of your `[sections]`:

----
	user = nut

	[myups]
		driver = mge-shut
		port = /dev/ttyS0
----

== upsc, upsstats, and the other clients say 'access denied'.  The device communication port (serial, USB or network) permissions are fine, so what gives?

In this case, "access denied" means the access to linkman:upsd[8], not the
device communication port.  You're being denied since the system has no
permission to speak to `upsd` according to its access controls.

There can be due to various reasons. To fix it, check:

- the LISTEN directive in linkman:upsd.conf[5]. It should allow your
  local or remote access method,
- your firewall rules. Port '3493/tcp' must be opened to incoming connections,
- your *tcp-wrappers* configuration (`hosts.allow` and `hosts.deny`) if used.

Refer to the linkman:upsd[8] and linkman:upsd.conf[5] man pages for more
information.

== I get a 'not listening on...' error from upsd.

Verify your LISTEN directive. It should be one of the valid IP addresses
for the computer running `upsd` (or `0.0.0.0`, which is `INADDR_ANY`), not
an address for a client.

The LISTEN directive lets you pick which interface `upsd` listens on.
If you are trying to limit the clients which can connect to `upsd`,
you either need to use tcp-wrappers or kernel firewall rules.

This isn't a NUT-specific limitation -- it applies equally to your web server
or mailer daemon.

== Which UPS should I buy?

One with a no-questions-asked money-back guarantee. Seriously. The NUT
developers cannot take responsibility for recommending an UPS (see the LICENSE
file for more details on the explicit lack of warranty), only to find out that
the manufacturer has changed the internals of the UPS without changing the
model name.

That said, from time to time, certain vendors have helped out by providing
hardware for testing, results of their testing efforts, or protocol
specifications. We try to publish this information on the NUT website, so you
can take this into consideration when selecting an UPS brand.

== I have an APC Smart-UPS connected with a grey APC serial cable and it won't work.

The Back-UPS type in the genericups driver works but then I don't get to use
all the nifty features in there.  Why doesn't the right driver work?

The problem lies in your choice of cable.  APC's grey cables
generally only do "dumb" signalling -- very basic yes/no info about
the battery and line status.  While that is sufficient to detect a
low battery condition while on battery, you miss out on all the
goodies that you paid for.

Note that the 940-0095B happens to be a grey cable, but it is actually
a dual mode cable and can be used in smart mode.  If you have
this cable, you need to edit your ups.conf to look like this:

	[myups]
		driver = apcsmart
		port = /dev/whatever
		cable = 940-0095B

All other grey cables from APC are assumed to be "dumb".

If your grey cable isn't the 940-0095B, the solution is to dump that
cable and find one that supports APC's "smart" signalling.  Typically
these come with the UPS and are black.  If your smart cable has
wandered off, one can be built rather easily with some connectors and
cable -- there's no fancy wiring or resistors.

See this URL for a handy diagram:
https://www.networkupstools.org/cables/940-0024C.jpg

There is also a text version of that diagram in the docs/cables
directory of the NUT source distribution.  Either one should allow
you to build a good clone of APC's 940-0024C cable.

There are simpler solutions involving 3 wires that work just fine
too, but Powerchute won't find the loopback DTR-DCD and RTS-CTS and
will be annoyed.  If you don't ever plan to use Powerchute, 3 wires
(RxD, TxD, GND) are sufficient.

It should also be noted that the genericups driver has no way to
detect the UPS, so it will fire up quite happily if it can open the
serial port.  Merely having it start up is not necessarily an
indication of success.  You should start it and then check the
status with upsc or similar to be sure that it's reading the
hardware properly.

== Why doesn't upsd implement the functionality of upsmon?  I have to run THREE programs to monitor my UPS!

*Answer 1*

We try to follow the "tool for the job" philosophy of Unix.  It may mean
more programs running, but the flexibility you get is usually
worth it.

Yes, the machine with the UPS attached will generally have 3
processes (driver, `upsd`, `upsmon`) running, but this design allows
a much bigger setup.  Imagine a data room with a bunch of machines
all drawing power from the same UPS.  Only one can be connected by a
serial or USB cable, and the rest of them just run an `upsmon` client.

Besides, if `upsmon` were rolled into `upsd`, `upsd` would get even
bigger than it is now.  You'd have one less process, but the
RAM consumption would be pretty close to what you have now -- but
consumed on each system involved.

See the "Data Room" section in link:docs/config-notes.txt[] for
more configuration ideas and explanations.

*Answer 2*

If this really bothers you, roll up your sleeves and use the
linkman:sockdebug[8]] code to write a "upsmon" type program that sits on
top of the state sockets.  It won't work over the network, but it means
you don't need `upsd`.  It also means only one host can monitor the
UPS.

This is also a good option to consider if you can't use networked
monitoring code for security or safety reasons.

*Answer 3*

There are plans in the queue... for a long time... to extend `upsd` data
server and the NUT clients with ability to use a local Unix socket for the
NUT Networked protocol. This would also allow to forgo the dependency on
TCP/IP stack for communications within one machine.

See the TODO file for more on this and other related topics.

== Why isn't upssched part of upsmon?

Most users will never have any reason to use `upssched`.  It's
complicated, and getting it right for your situation can be tricky.
Having it live in a separate program saves resources and lets most
people avoid it completely.

It is also coherent with the answer to the previous question.

== Why doesn't upsmon send a SIGPWR signal to init so it can deal with power events?

*Answer 1*

New versions of the `init` man page taken from the *sysvinit* package
are saying that usage of `SIGPWR` is discouraged, since `/dev/initctl`
control channel is the preferred way of communication.

*Answer 2*

The name of the game is portability.  Not everyone's `init` handles
that kind of signalling gracefully.  What's more, some admins
might want to do things differently even if they have that kind of
`init` running.

So, to be compatible, upsmon just invokes a shell command.  If you
want to use init's `SIGPWR` stuff, just put the right "kill" line in
a shell script and make your `upsmon` call it.  Everyone wins.

== Why won't bestups talk to my Best Fortress UPS?

There are at least two different protocols being used for hardware
with very similar names.  The bestups driver tends to support the
units built around the newer "PhoenixTec" protocol, and the bestfortress
driver supports the older Best hardware.

There is a similar problem with the tripplite_usb driver: it only supports the
older, proprietary protocol. Newer standards-compliant Tripp Lite UPS models
are supported by usbhid-ups. We name drivers based on the information
available at the time the driver was first written, which often is incomplete.

== What's this about 'data stale'?

It means your UPS driver hasn't updated things in a little while.
upsd refuses to serve up data that isn't fresh, so you get the
errors about staleness.

If this happens to you, make sure your driver is still running.
Also look at the syslog.  Sometimes the driver loses the connection
to the UPS, and that will also make the data go stale.

This might also happen on certain virtualization platforms. If you cannot
reproduce the problem on a physical machine, please report the bug to the
virtualization software vendor.

If this happens a lot, you might consider cranking up DEADTIME
in the upsmon.conf to suppress some of the warnings for shorter
intervals.  Use caution when adjusting this number, since it
directly affects how long you run on battery without knowing
what's going on with the UPS.

Note: some drivers occasionally need more time to update than the
default value of MAXAGE (in `upsd.conf`) allows.  As a result, they
are temporarily marked stale even though everything is fine.  This
can happen with MGE Ellipse equipment -- see the linkman:mge-shut[8]
or linkman:usbhid-ups[8] man pages.  In such cases, you can raise
the value of MAXAGE to avoid these warnings; try a value like 25 or 30.

== Why do the client programs say 'Driver not connected' when I try to run them?

*Answer 1*

This means that `upsd` can't connect to the driver for some reason.
Your `ups.conf` entry might be wrong, or the driver might not be
running.  Maybe your state path is not configured properly.

Check your syslog.  upsd will complain regularly if it can't
connect to a driver, and it should say why it can't connect.

Note: if you jumped in with both feet and didn't follow the link:INSTALL.nut[]
document, you probably started `upsd` by itself.  You have to run
`upsdrvctl start` (explicitly -- on legacy systems only) to start
the drivers after configuring `ups.conf`.

On operating systems with a supported service management framework,
you might wrap your NUT drivers into individual services instances
with `upsdrvsvcctl resync` and then manage those with commands like
`upsdrvsvcctl stop` and `upsdrvsvcctl start` (note that on other
systems this tool may be not pre-installed via packaging).

In fact, service instances prepared by the `nut-driver-enumerator` script
and service based on contents of your `ups.conf` file and automatically
maintained by the respective framework can conflict with manual execution
of drivers, so `upsdrvctl` would emit a warning in NUT builds with that
capability (can be silenced by exporting a `NUT_QUIET_INIT_NDE_WARNING`
environment variable with any value).

*Answer 2*

Some USB UPS devices have unreliable USB to serial interfaces.
In that case, it's advised to unplug / plug the device and try again.

If that resolves the issue, you should consider resetting the USB hub the
device is attached to before starting the nut driver, using `usb_resetter`
script (for Linux) from https://github.com/netinvent/usb_resetter

See files under `scripts/usb_resetter/` in NUT sources for more information.

== Why don't the pathnames in your documentation match the package I installed?

Each distribution has conventions for where specific file types should be
stored. The NUT project cannot possibly track all of these conventions, so the
documentation assumes the default installation directory prefix of
`/usr/local/ups` when describing file locations. It also allows custom
builds of NUT to minimally conflict with files of a packaged installation.

The distributions tend not to change the base name of the files, so you
can search for drivers and configuration files in the package database
of installed files. For instance, on Debian or Ubuntu derivatives, you
can use `dpkg --search usbhid-ups` to see where the drivers are stored.

== Everything works perfectly during the shutdown, and the UPS comes back on, but my system stays off.  What's happening?

Assuming you don't have the problem in the next question, then you
probably have an ATX motherboard, have APM or ACPI enabled in your
kernel (assuming Linux here), and are reaching the 'halt' at the
bottom of your shutdown scripts.

Your machine obeys and shuts down, and stays down, since it
remembers the 'last state' when the UPS restarts.

One solution is to change your shutdown scripts so you never reach
that point.  You *want* the system to die without reaching the
part where the kernel tells it to shut down.  A possible script
might look like this (see `scripts/systemd/nutshutdown` in NUT
sources for a more streamlined and modern variant):

------
	# other shutdown stuff here (mount -o remount,ro ...)
	# `upsmon -K` if available on still mounted filesystems
	# at this point is more portable than the `test` below

	if (test -f /etc/killpower || /sbin/upsmon -K)
	then
		/sbin/upsdrvctl shutdown

		sleep 600	# this should never return

		# uh oh, we never got shut down! (power race?)
		reboot
	fi

	halt -p
------

The other solution is to change your BIOS setting to "always power
on" instead of "last state", assuming that's possible.

== My system has an ATX power supply.  It will power off just fine, but it doesn't turn back on.  What can I do to fix this?

This depends on how clueful your motherboard manufacturer is, and
isn't a matter of the OS.  You have to do one of the following
things depending on what's supported:

- Set a jumper on the motherboard that means "return after outage"
- Set something in the BIOS that says "power up after power failure"
- Try using something (like a capacitor) across the power button
  to "push" it for you -- this might not work if it needs a delay
- Hack the cable between the power supply and the motherboard to fool
  it into powering up whenever line power is present
- Teach a monkey to watch the machine and press the power button
  when the outage is over.
  This might work, but it creates high produce bills.

If you can't use one of the first two options, give the board to
an enemy.  Let them worry about it.

== My Mac won't power back up by itself into Linux after the UPS shuts down.  What can I do about this?

This is about the same situation as the ATX question above, only
worse.  Earlier Macs apparently supported a hack where you could
cat some magic characters at `/dev/adb` to enable "server mode".
This would instruct the system to reboot while unattended.

From Usenet post <6boftzxz51.fsf@ecc-office.sp.cs.cmu.edu>:
------
	# Send packet over the ADB bus to the PowerMac CUDA chip
	# telling it to reboot automatically when power is restored
	# after a power failure.

	cat /etc/local/autoboot.adb > /dev/adb

    # autoboot.adb contains these three bytes (in hex):  01 13 01
------

Later PowerPC Macs with a PMU and the appropriate kernel driver can achieve the
same effect with the following command:

   echo server_mode=1 > /proc/pmu/options

The following pages have some slightly more kludgy answers which involve the
use of `setpci`, and are highly model-specific:

 - https://www.mythic-beasts.com/support/servers/colo/macminicolo_howto
 - http://superuser.com/questions/212434/reboot-after-power-failure-for-mac-running-ubuntu
 - http://ubuntuforums.org/showthread.php?t=1209576

Note: this question has been in the FAQ for several years now, and
there's still no clean answer.  Let me guess: everyone who runs a server
on Mac hardware has a team of trained monkeys, and feeds them
by growing bananas in the tropical environment formed by waste heat
from the equipment.

The rest of us are still waiting for the answer.  Booting into the
Mac OS to frob the "file server" panel is not an acceptable
solution.

== My Mac won't power back up by itself into Mac OS X after the UPS shuts down.  What can I do about this?

This is relatively simple to fix.  If you have console or VNC access, log in as
an administrator, go to System Preferences, click on Energy Saver, click on the
options tab, check "Restart automatically after a power failure".

Alternatively, you can connect via SSH and run `sudo pmset autorestart 1` to
achieve the same effect.

== I want to keep the drivers and upsd in their own security domains. How can this be accomplished?

Using a few role accounts and a common group, you can limit access
to resources such as the serial port(s) leading to the UPS
hardware.

This is just an example.  Change the values to suit your systems.

- Create a user called 'nutdev' and another called 'nutsrv'.  Put
them both in a group called 'nut'.

- Change the owner of any serial ports that will be used to nutdev,
and set the mode to 0600.  Then change the ownership of your state
directory (usually /var/state/ups) to nutdev.nut.

For my development system this yields the following /dev entries:

	0 crw-------   1 nutdev   tty        4,  64 Sep  3 17:11 /dev/ttyS0
	0 crw-------   1 nutdev   tty        4,  65 Sep  3 17:11 /dev/ttyS1

- Switch to root, then start the drivers:

	# upsdrvctl -u nutdev start

- The listing for /var/state/ups then looks like this:

	4 drwxrwx---   2 nutdev   nut          4096 Aug 20 18:37 .
	4 drwxr-xr-x   4 root     root         4096 May 14 21:20 ..
	4 srw-rw----   1 nutdev   nut             0 Sep  3 17:10 apcsmart-ups1
	4 srw-rw----   1 nutdev   nut             0 Sep  3 17:10 blazer_ser-ups2

You may have to remove old socket or state files first if you are
changing to this security scheme from an older version.  The drivers
will create new files with the right owners and modes.

Note that `/var/state/ups` is group writable since `upsd` will
place the `upsd.pid` file here by default.

You may have to change the groups of `upsd.conf` and `upsd.users` to
make them readable to the NUT `upsd` program.  These files should not
be owned nor writable by `nutsrv`, since someone could compromise the
daemon and change the config files.  Instead, put `nutsrv` in a group
(`nut` in this example), then make the files owned by `root.nut`, with
POSIX bits mode `0640`.

Once the config files are ready, start upsd:

	:; upsd -u nutsrv

Check your syslog to be sure everything's happy, then be sure to
update your startup scripts so it uses this procedure on your next
boot.

If you like this, you'll probably also find the linkmanext:chroot[2] process
to be useful and interesting.  See link:security.txt[] for more details.

== What's the point of that 'security domains' concept above?

The point is limiting your losses.  If someone should happen to
break into `upsd` in that environment, they should only gain access
to that one user account.  Direct access to the serial device is
not possible, since that is owned by another user.

There is also the possibility of running the drivers and `upsd` in a
chroot jail.  See the `chroot` option in link:security.txt[], `upsd`
and driver documentation.

Why give would-be vandals any sort of help?

Put it this way -- I *wrote* good chunks of this stuff, and I still
run the programs this way locally.  You should definitely consider
using this technique.

== How can I make upsmon shut down my system after some fixed interval?

You probably don't want to do this, since it doesn't maximize your
runtime on battery.  Assuming you have a good reason for it (see
the next entry), then look at link:scheduling.txt[] or the
linkman:upssched[8] man page for some ideas.

/////////////////////////////////////////////////////////////////
TODO: figure out how to link to the upssched man page above.
/////////////////////////////////////////////////////////////////


== Why doesn't upsmon shut down my system?  I pulled the plug and nothing happened.

Wait.  The `upsmon` client doesn't consider a UPS to be critical until it's
*both* 'on battery' and 'low battery' at the same time.  This is by design.
Nearly every UPS supports the notion of detecting the low battery
all by itself.  When the voltage drops below a certain point, it
_will_ let you know about it.

If your system has a really complicated or time-consuming shutdown procedure,
you might need to shut down before the UPS raises the low battery flag.
For most users, however, the default behavior is adequate.

Ask yourself this: why buy a nice big UPS with the matching battery
and corresponding runtime and then shutdown early?  If anything, I'd
rather have a few more minutes running on battery during which the
power might return.  Once the power's back, it's business as usual
with no visible interruption in service.

If you purposely shut down early, you guarantee an interruption in
service by bringing down the box.

See link:upssched.txt[] for information on how you can shutdown early if
this is what you really want to do.

== The CGI programs report 'access to that host is not authorized' --  what's going on?

Those programs need to see a host in your hosts.conf before they
will attempt communications.  This keeps people from feeding it
random `host=` settings, which would annoy others with outgoing
connection attempts from your system.

If your linkman:hosts.conf[5] turns out to be configured correctly with
proper `MONITOR` entries and all that, check the permissions.  Your web
server may be running the CGI programs as a user that can't read
the file.

If you run your web server in a chroot jail, make sure the programs
can still read `hosts.conf`.  You may have to copy it into the jail
for this to work.  If you do that, make sure it's not writable by
any of the user accounts which run inside the jail.

== upsd is running, so why can't I connect to it?

Assuming you haven't changed the TCP port number on the command line or at
compile-time, then you may have some sort of firewall blocking the connection.

`upsd` listens on TCP port '3493' by default. If you do not specify a `LISTEN`
directive in `upsd.conf`, `upsd` only listens on the loopback interface.
See the linkman:upsd.conf[5] man page for details.

== How do you make upsmon reload the config file?

Or a variation like...

== How do you make upsd reload the config file?

Either find the pid of the background process and send it a SIGHUP,
or just start it again with '-c reload' (requires that the previously
started daemon saves a PID file).

If you send the signals yourself instead of using -c, be sure you
hit the right process.  There are usually two `upsmon` processes, and you
should only send signals to one of them.  To be safe, read the PID
file.

If your daemons are managed as systemd units, it is more idiomatic to
use the framework commands, e.g. `systemctl reload nut-server` (upsd)
or `systemctl reload nut-monitor` (upsmon). Note that the implementation
of `nut-server.service` by default starts `upsd -F` and does not save a
PID file; if your workflow requires to use plain `upsd -c reload`, you
should customize the unit (with a drop-in file) to start `upsd -FF`.

NUT releases after 2.8.0 define aliases for these units, so if your Linux
distribution uses NUT-provided unit definitions, `systemctl reload upsd`
may also work.

== I just bought a new WhizBang UPS that has a USB connector.  How do I monitor it?

There are several driver to support USB models.

- linkman:usbhid-ups[8] supports various manufacturers complying to
  the HID Power Device Class (PDC) standard,
- linkman:tripplite_usb[8] supports various older Tripp-Lite units
  (with USB ProductID 0001)
- linkman:bcmxcp_usb[8] supports various Powerware units,
- linkman:blazer_usb[8] supports various manufacturers that use the
  Megatec / Q1 protocol.
- linkman:nutdrv_qx[8] supports various manufacturers that use the wider
  Megatec / Q* protocol family. This is the driver slated to receive all
  further development in this area, it was specially designed to support
  many more sub-drivers and has added a lot over time, so please do try
  it first nowadays.
- linkman:apc_modbus[8] supports some APC branded devices built after 2010
  (requires to be built against a libmodbus version with RTU USB support)

Refer to the respective 'driver-name' (8) man page for more information.

You can also consult the Hardware Compatibility List (HCL) and filter on USB:
https://www.networkupstools.org/stable-hcl.html?connection=USB

== My USB UPS has a bogus Vendor ID 0x0001 and Product ID 0x0000, what driver supports it?

Unfortunately, many devices are made without registering as a Vendor with
the corresponding standards body, and use generic USB chips for interfacing
with a computer (roughly similar to using a network interface card with a
random MAC address and PCI ID, and thus poorly identifiable device specifics
needed to automatically load some certain driver). Often they also lack a
unique serial number field, so monitoring several devices is problematic.

One frequent case is with devices identifying as "Fry's Electronics" and/or
"MEC0003", if those metadata are served at all, or plain "0001/0000" in ID
field. In some cases they are accompanied by "UPSmart" software with a
"MEGA(USB)" connection option that works for Windows users.

Your best bet is to search for community discussions of issues on NUT GitHub
at https://github.com/networkupstools/nut/issues?q=is%3Aissue and try options
there. Devices with these chips were known to connect with drivers for such
unrelated protocols as Megatec Q* (different sub-drivers, often `fabula` or
`hunnox`), ATCL, or USB-HID.

== My USB UPS is supported but doesn't work!

On Linux, udev rules are provided to set the correct permissions on device
file. This allows the NUT driver to communicate with the UPS, through this
device file.

However, the driver may still fail to start and support the device, with a
message like:

	failed to claim USB device: could not claim interface 0: Operation not permitted

*Operation not permitted* is a message pointing to a privilege issue.
The most frequent issue is that udev has not actually applied the rule:

- if NUT has been freshly installed,
- and if the device USB cord was already plugged when installing NUT.

In this case, just unplug and plug back the USB cord, then restart NUT.
Instead of unplugging, you might also be able to run `udevadm trigger
--subsystem-match=usb --action=change` to fix permissions.

There was a mistake in the naming of the NUT udev rules file which resulted in
the rules being overridden by another udev configuration file. While this has
been fixed in the Git master branch, your distribution may still be affected.
Details are available in the following GitHub issue:
https://github.com/networkupstools/nut/issues/140

There may also be a conflict with an already running instance of the driver,
e.g. when a systemd unit instance `nut-driver@yourdevicename.service` was
automatically created and started by the `nut-driver-enumerator`, and then
you try to follow older revisions of the NUT documentation or blogs, and
start another copy with `upsdrvctl` (which should only be used on legacy
systems nowadays).

== Why do you not use the Linux kernel HID driver when communicating with USB UPSes?

When the `usbhid-ups` was first written, it replaced an older driver `hidups`
which used the Linux kernel USB HID API. At the time, the kernel HID API could
not distinguish between identical Usage IDs that were nested in different
parent IDs, so many common measurements were not available from `hidups`. For
this reason, the libusb approach was chosen, which has the added side effect
of being more portable than the Linux HID API. The Linux hiddev device nodes
have very similar permissions problems as the `/dev/bus/usb` nodes that the
libusb approach uses.

Due to difficulties in running libusb on OS X and Windows, those platforms
might actually benefit more from a native HID approach.

== I get a message from the kernel that the driver "did not claim interface 0 before use"

On Linux, if two copies of a driver are competing for the UPS, these messages
will appear in dmesg:

	usbfs: process 29641 (usbhid-ups) did not claim interface 0 before use

This can be a symptom of a source install conflicting with a package install.
There is a rudimentary locking mechanism in NUT, but there is a chance that the
packages might not use the same directory as the NUT default, and the conflict
will be reported by the kernel.

Also see above about conflicts between driver instances started by a service
management framework like systemd and started manually (e.g. with `upsdrvctl`).

== Why does my (Eaton 5E) USB UPS on Linux connect but quickly disconnects soon?

This issue was extensively investigated by NUT community members in
https://github.com/networkupstools/nut/issues/630 and resulted in a
chain of distribution bugs logged such as
https://bugzilla.redhat.com/show_bug.cgi?id=1715504

The gist of it is that some versions of Linux kernel used an "USB HID quirk"
for certain devices, see Linux kernel source `drivers/hid/hid-quirks.c` file,
including MGE/Eaton vendor ID (0x0463) based on an older device a contributor
had issues with. Firmware in newer devices no longer had the bug which needed
the "quirk" and misbehaved when it was enabled. While newer (and much older)
Linux kernels should not have the problem, with the quirk removed according
to https://lkml.org/lkml/2018/11/26/580 having the issue in the field really
depends on the combination of Linux kernel and device firmware that meet.

Either way, it seems that problematic combinations preclude Linux from seeing
the device as a `hid-generic` first, to hand it over to a NUT driver.

This quirk can be tuned with a kernel boot parameter (via GRUB etc.):

	usbhid.quirks=0x0463:0xffff:0x08

to re-enable the NOGET quirk.

For context, according to https://bugzilla.redhat.com/show_bug.cgi?id=1875532
the symptoms for the problem look like this:

	# Plug in the UPS and observe the dmesg logs,
	# the following continuously appears:
	[   93.568082] usb 1-6: new full-speed USB device number 9 using xhci_hcd
	[   94.311469] usb 1-6: New USB device found, idVendor=0463, idProduct=ffff, bcdDevice= 0.01
	[   94.311475] usb 1-6: New USB device strings: Mfr=1, Product=2, SerialNumber=0
	[   94.311483] usb 1-6: Product: 5E
	[   94.311486] usb 1-6: Manufacturer: EATON
	[   96.269989] hid-generic 0003:0463:FFFF.000A: hiddev96,hidraw2: USB HID v1.10 Device [EATON 5E] on usb-0000:00:14.0-6/input0
	[  107.369425] hid-generic 0003:0463:FFFF.000A: usb_submit_urb(ctrl) failed: -1
	[  107.369469] hid-generic 0003:0463:FFFF.000A: timeout initializing reports
	[  112.828826] usb 1-6: USB disconnect, device number 9
	[  113.284452] usb 1-6: new full-speed USB device number 10 using xhci_hcd
	[  114.027693] usb 1-6: New USB device found, idVendor=0463, idProduct=ffff, bcdDevice= 0.01
	[  114.027698] usb 1-6: New USB device strings: Mfr=1, Product=2, SerialNumber=0
	[  114.027701] usb 1-6: Product: 5E
	[  114.027704] usb 1-6: Manufacturer: EATON
	[  115.984222] hid-generic 0003:0463:FFFF.000B: hiddev96,hidraw2: USB HID v1.10 Device [EATON 5E] on usb-0000:00:14.0-6/input0
	[  126.825756] hid-generic 0003:0463:FFFF.000B: usb_submit_urb(ctrl) failed: -1
	[  126.825775] hid-generic 0003:0463:FFFF.000B: timeout initializing reports
	[  132.527809] usb 1-6: USB disconnect, device number 10

A similar report on the driver side may look like:

	usbhid-ups[4554]: libusb_get_report: Input/output error
	upsd[4591]: Data for UPS [eaton] is stale - check driver
	usbhid-ups[4554]: Can't claim USB device [0463:ffff]: No such file or directory
	upsd[4591]: Can't connect to UPS [eaton] (usbhid-ups-eaton): No such file or directory
	upsmon[5148]: Poll UPS [eaton@localhost] failed - Driver not connected
	upsmon[5148]: Communications with UPS eaton@localhost lost

Other similar looking issues may include improper setup of udev, upower
and similar frameworks to hand over the device from the OS to a driver
daemon; competition with other software probing USB devices (ModemManager
was mentioned in this context), including running several copies of the
NUT drivers trying to use same port (e.g. one started by services and
another manually as you tried to debug the problems).

Software quirks aside, please do test with a different USB cable and/or port
on the computer. These were known to cause grief beyond what can be fixed
with a few key words ;)

Finally, sometimes the issue is on the OS side (and/or USB chipset), to
the point that the USB driver can not be unloaded and re-attached until
you power cycle the system.

== Why doesn't my package work?

Or a variation like...

== I can't run this because there's no package for it.  Why isn't this in a package yet?

Sorry, can't help you there.  All official releases are source code
and are posted on https://www.networkupstools.org/ along with PGP
signatures for verification.

This means all packages have been built by a third party.  If you
have an issue that's related to packaging, you will need to seek
help with whoever built it for you.

== My UPS is directly connected to an appliance with a limited version of NUT, how can I monitor the UPS from arbitrary clients?

You can set up a separate general-purpose system as the NUT server for
your "arbitrary clients", using `dummy-ups` in "relay mode" as the driver.
This instance of `dummy-ups` would in turn be the NUT client allowed to
interact with the appliance and that way with the UPS connected there.

NOTE: The original question related to a NAS with NUT provided in its
firmware OS, that only allowed one or few clients and not a whole
rack's worth of client IP addresses.

== My networked UPS can't handle being monitored by dozens of NUT clients

Network management cards on many UPSes are rather puny appliances, often
known to either limit the amount of clients who may connect, for security
or performance reasons, or otherwise to crash or respond very slowly when
overwhelmed.

You may be better off reducing the amount of servers connected to the UPS
with the `snmp-ups`, `netxml-ups` or similar type of driver, and set up
other systems as clients of these NUT servers.

Developers who are working on NUT, its drivers, or further projects and
appliances based on NUT, and who need to monitor their UPS from multiple
systems using the complete NUT stack on each system (e.g. during testing),
can benefit from dedicating a separate general-purpose system as the NUT
server using the real (networked) driver for the UPS, while using the
`dummy-ups` in "relay mode" as the driver connected to this dedicated
server on each tested system.

== How can I setup NUT as a proxy (setup a server to forward/relay client data)?

This can easily be achieved by using the `dummy-ups` driver.
The `port` field acts as the reference to the "other" UPS served
by another NUT server.

Example with `dummy-ups` driver:

----
[proxy]
	driver = dummy-ups
	port = upsname@ip-or-hostname[:port]
	desc = "UPS proxy for UPS upsname on server ip-or-hostname"
----

Also note that there is a `clone` driver with similar purpose,
which allows users to group clients to a particular outlet of
a device with a "real" driver running locally, and deal with
this output as if it was a normal UPS.

Here the `port` field references the driver socket name that
the "real" UPS driver is using. See its manual page for more
details and caveats.

Example with `clone` driver:

----
[realups]
	driver = usbhid-ups
	port = auto

[clone-outlet-1]
	driver = clone
	port = usbhid-ups-realups
	load.on = outlet.1.load.on
	load.off = outlet.1.load.off
	load.status = outlet.1.status
	[...]
----

This allows to group load attached to a separately manageable
outlet (or group of outlets) on larger UPS and ePDUs, in order
to power those devices on/off together. This may be also useful
to delegate management of feeds to devices for purposes like
hosting or supporting hardware for smaller teams sharing a rack
in a larger company.

== Why are there two copies of upsmon running?

It's not really two complete copies if your OS forks efficiently.

By default, `upsmon` runs most of the grunt work as an unprivileged
user and keeps a stub process around with 'root' powers that can
only shut down the system when necessary.  This should make it much
harder to gain 'root' in the event a hole is ever discovered in
`upsmon`.

If this really bothers you and you like running lots of code as
`root`, start `upsmon` with `-p` option, and it will go back to
being one big process.  This is not recommended, so don't blame
us if something bad happens in this mode.

== I get the following error while building: `make[4]: don't know how to make HP-UX/nut-drvctl.sh. Stop`

*Answer 1*

Current NUT codebase (since v2.8.0) is regularly tested with GNU, BSD and
Sun implementations of `make`, so seeing failures in release snapshots
(or iterations that made it to the master branch) is very surprising.
Please raise an issue on GitHub.

*Answer 2*

Older NUT codebase (release tarballs) has some hidden dependencies on
GNU Make which show up while running `make distcheck`. If you are running
`make distcheck` or its variants, you will need to install GNU Make
(`devel/gmake` in the ports tree), which is incidentally what the
official FreeBSD port of NUT does for all builds.

== I have 'some problem' with 'some old version' ...

Get the latest stable release, and see if it still happens.  If it
goes away, it means someone else reported it and got it fixed a
long time ago.

You may want to search the mailing lists to see if someone else has
experienced the same problem. If so, there is a good chance that someone else
has worked through the process necessary to shoehorn the latest NUT version
into your distribution (potentially with unofficial packages).

Some OS distributions contain old versions of NUT. If your hardware is newer
than the NUT release, there is a good chance that support has not been added
yet. Please do not tell us you have the "latest version for Distro XYZ" -- even
if the developers are familiar with that distribution, it helps others if you
quote the exact package version.

NOTE: Check the release date on the version you have.  If it's more
than about 6-12 months old, there's probably a newer stable tree
version out there. As development happens actively, be sure to also
check if a custom build from Git (usually using the `master` branch
of NUT https://github.com/networkupstools/nut/ repository) has your
issue fixed by some kind soul already.

== I can't connect with SSL using old NUT on an appliance

Unfortunately, some vendors do not issue new firmwares often, and even more
rarely do they significantly update any programs inside. It is not uncommon
to see NUT versions over a decade old delivered with small NAS boxes, for
example.

This may impact not only NUT protocol compatibility, but also transport
protocols such as SSL -- as cipher algorithms get outdated over time, and
ones deemed insecure are no longer handled at all (by default).  This is
not a problem limited to NUT: old SSH Key Exchange (kex) protocols or old
HTTPS mechanisms also become hard or impossible to use eventually.

On one hand, you can look into NUT configuration of `DISABLE_WEAK_SSL`.

On another, you can modify configuration of the newer system to allow older
algorithms as required by the older other system.

For NUT built against OpenSSL, the change would be in `/etc/ssl/openssl.cnf`
and similar to the diff block below:

----
--- a/etc/ssl/openssl.cnf
+++ b/etc/ssl/openssl.cnf
@@ -52,13 +52,6 @@ tsa_policy3 = 1.2.3.4.5.7
 
 [openssl_init]
 providers = provider_sect
+ssl_conf = ssl_sect
+
+[ssl_sect]
+system_default = system_default_sect
+
+[system_default_sect]
+CipherString = DEFAULT@SECLEVEL=0
 
 # List of providers to load
 [provider_sect]
----

Of course, keep in mind that by doing this you degrade your security level.
If better solutions are possible in your situation, prefer to follow them!

Thanks to Kajetan Rzepecki for doing the research and posting the findings
in https://github.com/networkupstools/nut/issues/1899

== I built NUT from Git, and it complains about lots of missing files. What happened?

If you are not actively developing a driver, can you use a snapshot instead?
The NUT instance of Buildbot generates tar files of the latest NUT source
after each successful build, and these snapshots include a pre-built version
of the `./configure` script.

WARNING: There is an outstanding bug that after the shutdown of BuildBot,
no regular distribution tarballs are in fact published.

To build from Git, you will need recent versions of autoconf, automake, libtool,
asciidoc, a2x and its dependencies for DocBook/dblatex. Rather than publish a
list of the exact versions needed (which will quickly become out of date), we
recommend you consult your distribution's dependency list for building a NUT
package, and use that as a starting point.

That said, for the numerous systems running build agents of the NUT CI farm,
their lists of dependency packages are available in `docs/config-prereqs.txt`
in NUT sources.

== Do I have to use a serial connection to monitor the UPS? What about direct network connections (SNMP or otherwise)?

NUT currently supports USB communication through several drivers,
and also SNMP and XML/HTTP (Eaton and MGE) communications.

Since NUT is very extensible, support for a new communication bus can be added
easily.

Any time there is a gap in features, it's usually because the
group of people who own that hardware and the group of people who
write code don't overlap.  The fix is to make them overlap -- turn
an owner into a developer or vice-versa.

== What happened to the patch I sent?

We try to prioritize emails with patches, but you should understand that a
simple fix for your bug might be complicated to integrate with the rest of
NUT. Changing the way a fundamental component works, such as USB support,
means a lot of testing to ensure that your fix does not break other drivers.

Sometimes patches are put on hold due to a feature freeze.  If it
doesn't show up once the new version opens up, please send it again.

It may also be much more productive to submit changes as pull requests via
https://github.com/networkupstools/nut/pulls so they are automatically
processed by the NUT CI farm across numerous target platforms, and
various inconsistencies can be diagnosed and fixed early.

== I'm not much of a programmer.  How can I help?

There's always work to be done outside of the realm of code bashing.
Documentation can always be improved.  A new user's perspective is
sometimes needed to appreciate this, since developers and long-time
users consider everything obvious.  Bug reports and pull requests
on any project's documentation are just as valuable as those for
the actual programs' sources.

Fielding questions on the mailing lists is also helpful.  This
lets other people to focus on coding issues while allowing the
original poster to get some information at the same time.  It's
quite a relief to open that mailbox and find that someone else
has already handled it successfully.

== I replaced the battery in my APC Smart-UPS and now it thinks the battery is low all the time.  How do you fix this?

Or a variation like...

== My APC UPS keeps reporting 'OL LB', even after it's been charging for many hours.  What can I do about this?

This happened to me, and some other people too.  The combination of
our experiences should prove useful to you.

First, you need to realize that the UPS apparently stores data about
the battery, load, and runtime.  After replacing the battery, it
needs to be clued in to the new situation.  If the traditional
runtime calibration doesn't work, you have to try something a
little more drastic.

You need to *completely* drain the UPS while it has a good ground.
This means you can't just pull the plug.  You also have to
disconnect it from the computer so this software won't shut it
down.

The easiest way to do this is to first unplug your computer(s) from
it, and plug in a token load like a lamp.  Also, move the UPS to a
power strip that doesn't switch the ground line or an outlet that
you can switch off at your panel.

Once the UPS is up at 100% charge (this is important), disconnect
the power.  It _must_ remain connected to the ground, or the
results may not be accurate.  Ignore the sounds it makes, and go
away until it's done.  Don't do anything to the front panel while
this is happening.

After all of this, put things back the way they should be and let
it charge up.  You should find that it again gives reasonable
values and behavior, as it was when it was new.

Thanks to Matthew Dharm for helping us nail down this procedure.

== upsstats returns temperatures in Celsius. I like Fahrenheit. Where's the config file to switch it back?

Temperature scales are handled by the template files, so edit your
upsstats.html and change it from TEMPC to TEMPF.

== Why is the mailing list ignoring me?

You probably asked a question that's answered in this FAQ, or
somewhere else in the documentation, and nobody wants to quote it
for you.

There is a small chance that the mailing list spam filter ate your message.
Check the list archives to see if your message appears there.
Also double-check that you have subscribed to the lists and completed
all the confirmation rituals of its engine.

Convincing the other subscribers that you've actually read down this
far might be useful.  You might mention "queequeg" for better results.

This URL may also be helpful:

http://www.catb.org/~esr/faqs/smart-questions.html

== Why are you so insistent about sending emails to public mailing lists instead of to individuals?

By and large, NUT is a volunteer effort. By emailing one person, you are
asking them to take care of your question. If you email the list instead, you
give others the opportunity to answer.

In addition, the mailing lists are publicly archived, and therefore easily
searchable. Chances are, you aren't the only person who will ever have that
question.

There are similar benefits to using the discussions on issue tracker at
https://github.com/networkupstools/nut/issues and if suitable, in the
currently open pull requests.

== If you want mailing list replies to go to the list, why don't you add a Reply-To: header?

We are not going to rehash all of the arguments for and against this in a
simple FAQ entry. If you intend for your reply to go to more than just the
last person who posted, it is not too much trouble to hit "Reply All".

== I found some information about another kind of UPS protocol you don't support yet, but I don't know what to do with it. Can you help?

If you're not a programmer, you can still help others by making
that protocol available.  You might host the document somewhere and
send the URL to one of the mailing lists.

Posting an issue with attachments on
https://github.com/networkupstools/nut/issues
can also be helpful.

== How can you answer questions to situations that nobody's encountered yet?  Isn't this a frequently asked questions file?

*Answer 1*

It's a kind of Magic.

*Answer 2*

It's both that and a frequently *anticipated* questions file, too.

The idea is to write it up in here so that nobody asks the mailing
list when it finally does get released.

== My UPS powers up immediately after a power failure instead of waiting for the batteries to recharge!
Or a variation like...

== My UPS (an APC as it happens) lacks the field "battery.charge.restart" -- so how will it know when to restart?

You can rig up a little hack to handle this issue in software.

Essentially, you need to test for the POWERDOWNFLAG in your *startup* scripts
while the filesystems are still read-only (before `upsmon` daemon has started
and removed it).  You can also query `upsmon -K` for presence of the file, to
avoid hard-coding the path or parsing it from your `upsmon.conf` file.  If the
flag is there, you know your last shutdown was caused by a power failure and
the UPS battery is probably still quite weak.

In this situation, your best bet is to sleep it off.  Pausing in your startup
script to let the batteries recharge with the filesystems in a safe state is
recommended.  This way, if the power goes out again, you won't face a situation
where there's not enough battery capacity left for upsmon to do its thing.

Exactly how long to wait is a function of your UPS hardware, and will require
careful testing.

If this is too evil for you, buy another kind of UPS that will either wait for
a minimum amount of charge, a minimum amount of time, or both.

== I'm facing a power race
Or a variation like...

== The power came back during the shutdown, but before the UPS power off. Now the UPS does not reboot, and my computer stays off. How can I fix that?

There is a situation where the power may return during the shutdown process.
This is known as a race.  Here's how we handle it.

"Smart" UPSes typically handle this by using a command that forces the UPS to
power the load off and back on.  This way, you are assured that the systems will
restart even if the power returns at the worst possible moment.

Contact closure units (ala genericups), on the other hand, have the potential
for a race when feeding multiple systems.  This is due to the design of most
contact closure UPSes.  Typically, the "kill power" line only functions when
running on battery.  As a result, if the line power returns during the shutdown
process, there is no way to power down the load.

The workaround is to force your systems to reboot after some interval. This way,
they won't be stuck in the halted state with the UPS running on line power.

Implement this by modifying your shutdown script like this:

------
	# `upsmon -K` if available on still mounted filesystems
	# at this point is more portable than the `test` below

	if (test -f /etc/killpower || /sbin/upsmon -K)
	then
		/sbin/upsdrvctl shutdown

		sleep 120

		# uh oh, we never got shut down! (power race?)
		reboot
	fi
------