nut-debian/docs/FAQ.txt

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

== I just upgraded, and ...
You have read link:UPGRADING[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.

== upsstats says 'Error: can't open template file (upsstats.html)'.
Go into your configuration path (/usr/local/ups/etc by default) and
copy the sample template files over to their real names.  The sample
template files are installed with 'make install' and can 
also be found inside the source distribution in the conf directory. 

== upsmon fails the login and says 'username required' now.
Go read the link:UPGRADING[UPGRADING] file again.

== 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 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.

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
ups.conf.  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 upsd, not the device
communication port.  You're being denied since the system has no
permission to speak to upsd according to the access controls.

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

- the LISTEN directive in upsd.conf. 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).

Refer to the upsd(8) and upsd.conf(5) manpages 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.

== 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: http://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*

I try to follow the "tool for the job" philosophy.  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.  The rest of them just run
upsmon.

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 now.

See data-room.txt for more configuration ideas and explanations.

*Answer 2*

If this really bothers you, roll up your sleeves and use the
sockdebug 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.

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 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 that time, 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.

Note: some very slow machines have trouble keeping up with the
serial ports during periods of extreme load.  My old 486 used to
flip between "stale" and "OK" while running backups.

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 mge-shut man page.
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?

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 INSTALL.nut
document, you probably started upsd by itself.  You have to run
'upsdrvctl start' to start the drivers after configuring ups.conf.

== 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:

	# other shutdown stuff here (mount -o remount,ro ...)

	if (test -f /etc/killpower)
	then
		/usr/local/ups/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:

	# /usr/local/ups/sbin/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.

You may have to change the groups of upsd.conf and upsd.users to
make them readable.  These files should not be owned 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 mode 0640.

Once the config files are ready, start upsd:

	# /usr/local/ups/sbin/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 chroot process to
be useful and interesting.  See 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.txt provided in the source 
distribution for an example implementation. 

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 scheduling.txt or the 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.  upsmon 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 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 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 hosts.conf turns out to be configured correctly with 
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
upsd.conf 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'.

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

== 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.

- usbhid-ups supports various manufacturers complying to the HID standard,
- tripplite_usb supports various Tripp-Lite units,
- bcmxcp_usb supports various Powerware units,
- blazer_usb supports various manufacturers that use the Megatec / Q1 protocol.

Refer to the 'driver-name' (8) manpage for more information.

== What is this usbhid-ups (formerly newhidups) about?

The basic USB UPS support was done until NUT 2.2 using hidups. To allow
a wider support accross platforms for USB/HID compliant devices,
usbhid-ups driver uses libusb (which is available for a wide range of
operating systems) and libhid (currently, a modified internal version
of it).

As of NUT 2.2, usbhid-ups completely replaces the legacy hidups driver,
and provides support for various manufacturers. At that time, newhidups was
renamed to usbhid-ups.

usbhid-ups is built automatically if possible (libusb development files
need to be installed) and installed by the "make install" command.

== 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 failed 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 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.

== 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 http://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.

== 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 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 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.

If that doesn't work, try the latest development version.

If your problem is STILL there, then contact the mailing lists.

NOTE: check the release date on the version you have.  If it's more
than about 6 months old, there's probably a newer stable tree
version out there.

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

No. NUT currently support 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?

If a release goes by and your patch hasn't been included, it was
probably dropped.  There can be a lot of patches waiting for 
inclusion at some points, and occasionally some have to be
rejected.

Design issues or severe coding style problems can be the reason
for this.  I try to point out what the problems are, but there are
limits.  See developers.txt for some pointers on submitting
patches.

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

== 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 might not always be so clear.  A user's perspective
is sometimes needed to appreciate this.  Bug reports on a project's
documentation are just as valuable as those for the actual source.

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.

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

== 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.

== 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!

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.  If it's 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:

	if (test -f /etc/killpower)
	then
		/usr/local/ups/sbin/upsdrvctl shutdown

		sleep 120

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