Description of Apcupsd from Wikipedia:

Apcupsd, short for APC UPS daemon, is a utility that runs on Linux, UNIX, macOS and Windows.It allows the computer to interact with APC UPSes. Apcupsd also works with some OEM-branded products (e.g. Hewlett-Packard) manufactured by APC.[1]:7[2][3]

Apcupsd is a free software equivalent of the APC’s proprietary PowerChute software. As of version 3.14, Apcupsd has support for the PowerChute Network Shutdown function as well as many other features.

Apcupsd runs in daemon mode so to keep a live connection with the UPS. Depending on the settings and type of connection, Apcupsd either polls the UPS to learn about its current state, or receives messages from the UPS itself (e.g. via SNMP traps). Possible types of connections to the UPS are USB, RS-232 or Ethernet.

Apcupsd can communicate with other instances of Apcupsd on other computers and maintain a client-server relationship with them. This way it is possible to power multiple computers with one UPS, even though only one of them is connected to the data port of the UPS.

The official APCUPSD User Manual can be found at http://apcupsd.org/manual/manual.html

To install apcupsd on Centos 

The install package for Centos is not part of the default repos, so we need to first add the epel repository if not already present:

yum install epel-release
yum update -y
yum install apcupsd

Then do:

[root@router1 ~]#
[root@router1 ~]# systemctl status apcupsd
● apcupsd.service – APC UPS Power Control Daemon for Linux
Loaded: loaded (/usr/lib/systemd/system/apcupsd.service; disabled; vendor preset: disabled)
Active: inactive (dead)
[root@router1 ~]# systemctl start apcupsd
[root@router1 ~]# systemctl status apcupsd
● apcupsd.service – APC UPS Power Control Daemon for Linux
Loaded: loaded (/usr/lib/systemd/system/apcupsd.service; disabled; vendor preset: disabled)
Active: active (running) since So 2021-05-16 14:32:45 CEST; 858ms ago
Process: 1583 ExecStartPre=/bin/rm -f /etc/apcupsd/powerfail (code=exited, status=0/SUCCESS)
Main PID: 1584 (apcupsd)
CGroup: /system.slice/apcupsd.service
└─1584 /sbin/apcupsd -b -f /etc/apcupsd/apcupsd.conf

Mai 16 14:32:45 router1 systemd[1]: Starting APC UPS Power Control Daemon for Linux…
Mai 16 14:32:45 router1 systemd[1]: Started APC UPS Power Control Daemon for Linux.
Mai 16 14:32:45 router1 apcupsd[1584]: apcupsd 3.14.14 (31 May 2016) redhat startup succeeded
[root@router1 ~]#

In a production environment you would most likely want to enable this on boot:

systemctl enable apcupsd

[root@router1 ~]# apctest

Below output gives an idea of what the apctest looks like.

As this is a KVM virtualized machine we do not have any UPS system present, hence the test will fail.

Note apcupsd cannot run with apctest, so you first need to stop apcupsd.

For a real UPS system, the apcupsd configuration file needs to be edited

/etc/apcupsd/apcupsd.conf

see below.

Using apctest

These are some of the options for apctest:

[root@router1 ~]# apctest –help
usage: apcupsd [options]
Options are as follows:
-b, don’t go into background
-d, –debug <level> set debug level (>0)
-f, –config-file <file> load specified config file
-k, –killpower, –hibernate put UPS into hibernation mode [*]
-o, –power-off turn off UPS completely [*]
-P, –pid-file specify name of PID file
-p, –kill-on-powerfail hibernate UPS on powerfail
-R, put SmartUPS into dumb mode
-t, –term-on-powerfail terminate when battery power fails
-T send debug to ./apcupsd.trace
-V, –version display version info
-h, –help display this help

[*] Only one parameter of this kind and apcupsd must not already be running.

Copyright (C) 2004-2009 Adam Kropelin
Copyright (C) 1999-2005 Kern Sibbald
Copyright (C) 1996-1999 Andre Hedrick
Copyright (C) 1999-2001 Riccardo Facchetti
apcupsd is free software and comes with ABSOLUTELY NO WARRANTY
under the terms of the GNU General Public License

Report bugs to apcupsd Support Center:
apcupsd-users@lists.sourceforge.net
[root@router1 ~]#

2021-05-16 14:35:39 apctest 3.14.14 (31 May 2016) redhat
Checking configuration …
sharenet.type = Network & ShareUPS Disabled
cable.type = USB Cable
mode.type = USB UPS Driver
apctest FATAL ERROR in apctest.c at line 313
Unable to create UPS lock file.
If apcupsd or apctest is already running,
please stop it and run this program again.
apctest error termination completed
[root@router1 ~]# systemctl stop apcupsd
[root@router1 ~]# systemctl status apcupsd
● apcupsd.service – APC UPS Power Control Daemon for Linux
Loaded: loaded (/usr/lib/systemd/system/apcupsd.service; disabled; vendor preset: disabled)
Active: inactive (dead)

Mai 16 14:32:45 router1 systemd[1]: Starting APC UPS Power Control Daemon for Linux…
Mai 16 14:32:45 router1 systemd[1]: Started APC UPS Power Control Daemon for Linux.
Mai 16 14:32:45 router1 apcupsd[1584]: apcupsd 3.14.14 (31 May 2016) redhat startup succeeded
Mai 16 14:32:55 router1 apcupsd[1584]: NIS server startup succeeded
Mai 16 14:33:55 router1 apcupsd[1584]: Communications with UPS lost.
Mai 16 14:35:52 router1 systemd[1]: Stopping APC UPS Power Control Daemon for Linux…
Mai 16 14:35:52 router1 systemd[1]: Stopped APC UPS Power Control Daemon for Linux.
[root@router1 ~]# apctest

2021-05-16 14:35:59 apctest 3.14.14 (31 May 2016) redhat
Checking configuration …
sharenet.type = Network & ShareUPS Disabled
cable.type = USB Cable
mode.type = USB UPS Driver
Setting up the port …
apctest FATAL ERROR in apctest.c at line 321
Unable to open UPS device.
If apcupsd or apctest is already running,
please stop it and run this program again.
apctest error termination completed
[root@router1 ~]#

[root@router1 ~]# systemctl start apcupsd
[root@router1 ~]# systemctl status apcupsd
● apcupsd.service – APC UPS Power Control Daemon for Linux
Loaded: loaded (/usr/lib/systemd/system/apcupsd.service; disabled; vendor preset: disabled)
Active: active (running) since So 2021-05-16 14:40:05 CEST; 4s ago
Process: 1632 ExecStartPre=/bin/rm -f /etc/apcupsd/powerfail (code=exited, status=0/SUCCESS)
Main PID: 1633 (apcupsd)
CGroup: /system.slice/apcupsd.service
└─1633 /sbin/apcupsd -b -f /etc/apcupsd/apcupsd.conf

Mai 16 14:40:05 router1 systemd[1]: Starting APC UPS Power Control Daemon for Linux…
Mai 16 14:40:05 router1 systemd[1]: Started APC UPS Power Control Daemon for Linux.
Mai 16 14:40:05 router1 apcupsd[1633]: apcupsd 3.14.14 (31 May 2016) redhat startup succeeded

[root@router1 ~]# apcaccess status
APC : 001,017,0422
DATE : 2021-05-16 14:40:15 +0200
HOSTNAME : router1
VERSION : 3.14.14 (31 May 2016) redhat
CABLE : USB Cable
DRIVER : USB UPS Driver
UPSMODE : Stand Alone
STARTTIME: 2021-05-16 14:40:05 +0200
STATUS : COMMLOST
MBATTCHG : 5 Percent
MINTIMEL : 3 Minutes
MAXTIME : 0 Seconds
NUMXFERS : 0
TONBATT : 0 Seconds
CUMONBATT: 0 Seconds
XOFFBATT : N/A
STATFLAG : 0x05000100
END APC : 2021-05-16 14:40:15 +0200
[root@router1 ~]#

Check the logfile for events, such as brown-outs or power failures (not much to see in this case as we do not have a working UPS attached):

tail -f /var/log/apcupsd.events

[root@router1 ~]# tail -f /var/log/apcupsd.events
2021-05-16 14:32:45 +0200 apcupsd 3.14.14 (31 May 2016) redhat startup succeeded
2021-05-16 14:33:55 +0200 Communications with UPS lost.
2021-05-16 14:35:52 +0200 apcupsd exiting, signal 15
2021-05-16 14:35:52 +0200 apcupsd shutdown succeeded
2021-05-16 14:40:05 +0200 apcupsd 3.14.14 (31 May 2016) redhat startup succeeded
2021-05-16 14:41:15 +0200 Communications with UPS lost.

Configuring apcupsd

root@router1 ~]# cat /etc/apcupsd/apcupsd.conf
## apcupsd.conf v1.1 ##
#
# for apcupsd release 3.14.14 (31 May 2016) – redhat
#
# “apcupsd” POSIX config file

#
# Note that the apcupsd daemon must be restarted in order for changes to
# this configuration file to become active.
#

#
# ========= General configuration parameters ============
#

# UPSNAME xxx
# Use this to give your UPS a name in log files and such. This
# is particulary useful if you have multiple UPSes. This does not
# set the EEPROM. It should be 8 characters or less.
#UPSNAME

# UPSCABLE <cable>
# Defines the type of cable connecting the UPS to your computer.
#
# Possible generic choices for <cable> are:
# simple, smart, ether, usb
#
# Or a specific cable model number may be used:
# 940-0119A, 940-0127A, 940-0128A, 940-0020B,
# 940-0020C, 940-0023A, 940-0024B, 940-0024C,
# 940-1524C, 940-0024G, 940-0095A, 940-0095B,
# 940-0095C, 940-0625A, M-04-02-2000
#
UPSCABLE usb

# To get apcupsd to work, in addition to defining the cable
# above, you must also define a UPSTYPE, which corresponds to
# the type of UPS you have (see the Description for more details).
# You must also specify a DEVICE, sometimes referred to as a port.
# For USB UPSes, please leave the DEVICE directive blank. For
# other UPS types, you must specify an appropriate port or address.
#
# UPSTYPE DEVICE Description
# apcsmart /dev/tty** Newer serial character device, appropriate for
# SmartUPS models using a serial cable (not USB).
#
# usb <BLANK> Most new UPSes are USB. A blank DEVICE
# setting enables autodetection, which is
# the best choice for most installations.
#
# net hostname:port Network link to a master apcupsd through apcupsd’s
# Network Information Server. This is used if the
# UPS powering your computer is connected to a
# different computer for monitoring.
#
# snmp hostname:port:vendor:community
# SNMP network link to an SNMP-enabled UPS device.
# Hostname is the ip address or hostname of the UPS
# on the network. Vendor can be can be “APC” or
# “APC_NOTRAP”. “APC_NOTRAP” will disable SNMP trap
# catching; you usually want “APC”. Port is usually
# 161. Community is usually “private”.
#
# netsnmp hostname:port:vendor:community
# OBSOLETE
# Same as SNMP above but requires use of the
# net-snmp library. Unless you have a specific need
# for this old driver, you should use ‘snmp’ instead.
#
# dumb /dev/tty** Old serial character device for use with
# simple-signaling UPSes.
#
# pcnet ipaddr:username:passphrase:port
# PowerChute Network Shutdown protocol which can be
# used as an alternative to SNMP with the AP9617
# family of smart slot cards. ipaddr is the IP
# address of the UPS management card. username and
# passphrase are the credentials for which the card
# has been configured. port is the port number on
# which to listen for messages from the UPS, normally
# 3052. If this parameter is empty or missing, the
# default of 3052 will be used.
#
# modbus /dev/tty** Serial device for use with newest SmartUPS models
# supporting the MODBUS protocol.
# modbus <BLANK> Leave the DEVICE setting blank for MODBUS over USB
# or set to the serial number of the UPS to ensure
# that apcupsd binds to that particular unit
# (helpful if you have more than one USB UPS).
#
UPSTYPE usb
DEVICE

# POLLTIME <int>
# Interval (in seconds) at which apcupsd polls the UPS for status. This
# setting applies both to directly-attached UPSes (UPSTYPE apcsmart, usb,
# dumb) and networked UPSes (UPSTYPE net, snmp). Lowering this setting
# will improve apcupsd’s responsiveness to certain events at the cost of
# higher CPU utilization. The default of 60 is appropriate for most
# situations.
#POLLTIME 60

# LOCKFILE <path to lockfile>
# Path for device lock file. This is the directory into which the lock file
# will be written. The directory must already exist; apcupsd will not create
# it. The actual name of the lock file is computed from DEVICE.
# Not used on Win32.
LOCKFILE /var/lock

# SCRIPTDIR <path to script directory>
# Directory in which apccontrol and event scripts are located.
SCRIPTDIR /etc/apcupsd

# PWRFAILDIR <path to powerfail directory>
# Directory in which to write the powerfail flag file. This file
# is created when apcupsd initiates a system shutdown and is
# checked in the OS halt scripts to determine if a killpower
# (turning off UPS output power) is required.
PWRFAILDIR /etc/apcupsd

# NOLOGINDIR <path to nologin directory>
# Directory in which to write the nologin file. The existence
# of this flag file tells the OS to disallow new logins.
NOLOGINDIR /etc

#
# ======== Configuration parameters used during power failures ==========
#

# The ONBATTERYDELAY is the time in seconds from when a power failure
# is detected until we react to it with an onbattery event.
#
# This means that, apccontrol will be called with the powerout argument
# immediately when a power failure is detected. However, the
# onbattery argument is passed to apccontrol only after the
# ONBATTERYDELAY time. If you don’t want to be annoyed by short
# powerfailures, make sure that apccontrol powerout does nothing
# i.e. comment out the wall.
ONBATTERYDELAY 6

#
# Note: BATTERYLEVEL, MINUTES, and TIMEOUT work in conjunction, so
# the first that occurs will cause the initation of a shutdown.
#

# If during a power failure, the remaining battery percentage
# (as reported by the UPS) is below or equal to BATTERYLEVEL,
# apcupsd will initiate a system shutdown.
BATTERYLEVEL 5

# If during a power failure, the remaining runtime in minutes
# (as calculated internally by the UPS) is below or equal to MINUTES,
# apcupsd, will initiate a system shutdown.
MINUTES 3

# If during a power failure, the UPS has run on batteries for TIMEOUT
# many seconds or longer, apcupsd will initiate a system shutdown.
# A value of 0 disables this timer.
#
# Note, if you have a Smart UPS, you will most likely want to disable
# this timer by setting it to zero. That way, you UPS will continue
# on batteries until either the % charge remaing drops to or below BATTERYLEVEL,
# or the remaining battery runtime drops to or below MINUTES. Of course,
# if you are testing, setting this to 60 causes a quick system shutdown
# if you pull the power plug.
# If you have an older dumb UPS, you will want to set this to less than
# the time you know you can run on batteries.
TIMEOUT 0

# Time in seconds between annoying users to signoff prior to
# system shutdown. 0 disables.
ANNOY 300

# Initial delay after power failure before warning users to get
# off the system.
ANNOYDELAY 60

# The condition which determines when users are prevented from
# logging in during a power failure.
# NOLOGON <string> [ disable | timeout | percent | minutes | always ]
NOLOGON disable

# If KILLDELAY is non-zero, apcupsd will continue running after a
# shutdown has been requested, and after the specified time in
# seconds attempt to kill the power. This is for use on systems
# where apcupsd cannot regain control after a shutdown.
# KILLDELAY <seconds> 0 disables
KILLDELAY 0

#
# ==== Configuration statements for Network Information Server ====
#

# NETSERVER [ on | off ] on enables, off disables the network
# information server. If netstatus is on, a network information
# server process will be started for serving the STATUS and
# EVENT data over the network (used by CGI programs).
NETSERVER on

# NISIP <dotted notation ip address>
# IP address on which NIS server will listen for incoming connections.
# This is useful if your server is multi-homed (has more than one
# network interface and IP address). Default value is 0.0.0.0 which
# means any incoming request will be serviced. Alternatively, you can
# configure this setting to any specific IP address of your server and
# NIS will listen for connections only on that interface. Use the
# loopback address (127.0.0.1) to accept connections only from the
# local machine.
NISIP 0.0.0.0

# NISPORT <port> default is 3551 as registered with the IANA
# port to use for sending STATUS and EVENTS data over the network.
# It is not used unless NETSERVER is on. If you change this port,
# you will need to change the corresponding value in the cgi directory
# and rebuild the cgi programs.
NISPORT 3551

# If you want the last few EVENTS to be available over the network
# by the network information server, you must define an EVENTSFILE.
EVENTSFILE /var/log/apcupsd.events

# EVENTSFILEMAX <kilobytes>
# By default, the size of the EVENTSFILE will be not be allowed to exceed
# 10 kilobytes. When the file grows beyond this limit, older EVENTS will
# be removed from the beginning of the file (first in first out). The
# parameter EVENTSFILEMAX can be set to a different kilobyte value, or set
# to zero to allow the EVENTSFILE to grow without limit.
EVENTSFILEMAX 10

#
# ========== Configuration statements used if sharing =============
# a UPS with more than one machine

#
# Remaining items are for ShareUPS (APC expansion card) ONLY
#

# UPSCLASS [ standalone | shareslave | sharemaster ]
# Normally standalone unless you share an UPS using an APC ShareUPS
# card.
UPSCLASS standalone

# UPSMODE [ disable | share ]
# Normally disable unless you share an UPS using an APC ShareUPS card.
UPSMODE disable

#
# ===== Configuration statements to control apcupsd system logging ========
#

# Time interval in seconds between writing the STATUS file; 0 disables
STATTIME 0

# Location of STATUS file (written to only if STATTIME is non-zero)
STATFILE /var/log/apcupsd.status

# LOGSTATS [ on | off ] on enables, off disables
# Note! This generates a lot of output, so if
# you turn this on, be sure that the
# file defined in syslog.conf for LOG_NOTICE is a named pipe.
# You probably do not want this on.
LOGSTATS off

# Time interval in seconds between writing the DATA records to
# the log file. 0 disables.
DATATIME 0

# FACILITY defines the logging facility (class) for logging to syslog.
# If not specified, it defaults to “daemon”. This is useful
# if you want to separate the data logged by apcupsd from other
# programs.
#FACILITY DAEMON

#
# ========== Configuration statements used in updating the UPS EPROM =========
#

#
# These statements are used only by apctest when choosing “Set EEPROM with conf
# file values” from the EEPROM menu. THESE STATEMENTS HAVE NO EFFECT ON APCUPSD.
#

# UPS name, max 8 characters
#UPSNAME UPS_IDEN

# Battery date – 8 characters
#BATTDATE mm/dd/yy

# Sensitivity to line voltage quality (H cause faster transfer to batteries)
# SENSITIVITY H M L (default = H)
#SENSITIVITY H

# UPS delay after power return (seconds)
# WAKEUP 000 060 180 300 (default = 0)
#WAKEUP 60

# UPS Grace period after request to power off (seconds)
# SLEEP 020 180 300 600 (default = 20)
#SLEEP 180

# Low line voltage causing transfer to batteries
# The permitted values depend on your model as defined by last letter
# of FIRMWARE or APCMODEL. Some representative values are:
# D 106 103 100 097
# M 177 172 168 182
# A 092 090 088 086
# I 208 204 200 196 (default = 0 => not valid)
#LOTRANSFER 208

# High line voltage causing transfer to batteries
# The permitted values depend on your model as defined by last letter
# of FIRMWARE or APCMODEL. Some representative values are:
# D 127 130 133 136
# M 229 234 239 224
# A 108 110 112 114
# I 253 257 261 265 (default = 0 => not valid)
#HITRANSFER 253

# Battery charge needed to restore power
# RETURNCHARGE 00 15 50 90 (default = 15)
#RETURNCHARGE 15

# Alarm delay
# 0 = zero delay after pwr fail, T = power fail + 30 sec, L = low battery, N = never
# BEEPSTATE 0 T L N (default = 0)
#BEEPSTATE T

# Low battery warning delay in minutes
# LOWBATT 02 05 07 10 (default = 02)
#LOWBATT 2

# UPS Output voltage when running on batteries
# The permitted values depend on your model as defined by last letter
# of FIRMWARE or APCMODEL. Some representative values are:
# D 115
# M 208
# A 100
# I 230 240 220 225 (default = 0 => not valid)
#OUTPUTVOLTS 230

# Self test interval in hours 336=2 weeks, 168=1 week, ON=at power on
# SELFTEST 336 168 ON OFF (default = 336)
#SELFTEST 336[root@router1 ~]#