1. Compile NUT from source
  
groupadd nut;adduser -g nut ups
  
yum install gd-devel libusb-devel
  
./configure --with-user=ups --with-group=nut --with-usb --with-cgi --prefix=/ups --localstatedir=/ups/var --with-pidpath=/ups/var/state/ups --with-statepath=/ups/var/state/ups --enable-static

make
  
make install
  
cd /ups;mkdir -p /ups/var/state/ups;chmod 0770 /ups/var/state/ups;chown root:nut /ups/var/state/ups
  
copy libz.so to /ups/lib
  
copy libz.a to /ups/lib
  
chmod 0660 /dev/ttyS0;chown root:nut /dev/ttyS0

cat >/etc/udev/rules.d/99-my.rules <<EOL
SUBSYSTEM=="tty", KERNEL=="ttyS0", OWNER="root", GROUP="nut"
EOL

For APC UPS BR550I or BR550GI use the ff.

vi /etc/udev/rules.d/52-nut-usbups.rules
# This file is generated and installed by the Network UPS Tools package.
ACTION!="add", GOTO="nut-usbups_rules_end"
SUBSYSTEM=="usb_device", GOTO="nut-usbups_rules_real"
SUBSYSTEM=="usb", GOTO="nut-usbups_rules_real"
BUS!="usb", GOTO="nut-usbups_rules_end"
LABEL="nut-usbups_rules_real"
# APC
#  various models  - usbhid-ups
ATTR{idVendor}=="051d", ATTR{idProduct}=="0002", MODE="664", GROUP="nut"
LABEL="nut-usbups_rules_end"

Prepare upsd.conf upsmon.conf ups.conf upssched.conf upsd.users

chown root:nut *.conf upsd.users
  
chmod 0640 *.conf upsd.users

add the following to /etc/init.d/halt

LD_LIBRARY_PATH=/ups/lib:$LD_LIBRARY_PATH
export LD_LIBRARY_PATH
if(test -f /etc/killpower)
then
        echo "***************SHUTTING DOWN UPS*************"
        sleep 1
        echo "5"
        sleep 1
        echo "4"
        sleep 1
        echo "3"
        sleep 1
        echo "2"
        sleep 1
        echo "1"
        sleep 1
        echo "bye!"
        sleep 1
        /ups/bin/upsdrvctl -u root shutdown
        echo "UPS should be off by now"
        sleep 20
fi

Add upsd upsmon startup scripts to /etc/rc.local

  
cat >/ups/etc/alerthandler <<EOL
#! /bin/sh
case $1 in
        onbattwarn)
                echo "The UPS has been on battery for awhile"
                /ups/sbin/upsmon -c fsd
        ;;
        ups-back-on-power)
                /bin/rm -f /ups/var/state/ups-on-battery
        ;;
        *)
                logger -t alerthandler "Unrecognized command: $1"
        ;;
        esac
EOL

chmod 0760 /ups/etc/alerthandler;chown root:nut /ups/etc/alerthandler

TEST

$ fuser /dev/ttyS0 # should produce no output
  
$ upsdrvctl start
  
# Output:
  
Network UPS Tools - UPS driver controller 2.4.3
  
Network UPS Tools - Megatec protocol driver 1.6 (2.4.3)
  
Megatec protocol UPS detected.
  
$ upsd
  
# Output:
  
Network UPS Tools upsd 2.4.3
  
listening on 127.0.0.1 port 3493
  
listening on 192.168.1.145 port 3493
  
Connected to UPS [myups]: megatec-myups
  
  
$ upsc myups@localhost
  
# Output:
  
battery.charge: 100.0
  
...
  
ups.type: standby