Prerequisits

sudo yum install centos-release-scl
sudo yum install devtoolset-8
sudo yum install git cmake3 gcc-c++ gcc binutils \
libX11-devel libXpm-devel libXft-devel libXext-devel openssl-devel
sudo yum install gcc-gfortran pcre-devel \
mesa-libGL-devel mesa-libGLU-devel glew-devel ftgl-devel mysql-devel \
fftw-devel cfitsio-devel graphviz-devel \
avahi-compat-libdns_sd-devel openldap-devel python-devel \
libxml2-devel gsl-devel

Install ROOT from source and compile with gcc8

scl enable devtoolset-8 bash
mkdir ROOT
cd ROOT
git clone --branch v6-22-00-patches https://github.com/root-project/root.git root_src    
mkdir build  install
cd build
cmake3 -DCMAKE_INSTALL_PREFIX=../install  ../root_src      
cmake3 --build .  -j8  --target install
cd ..
source install/bin/thisroot.sh 

Configure repositories

sudo cat > /etc/yum.repos.d/xdaq.repo <<EOF
[xdaq]
name=XDAQ Software Core
baseurl=http://xdaq.web.cern.ch/xdaq/repo/core/15/cc7/x86_64/RPMS/
enabled=1
gpgcheck=0
[xdaq-worksuite]
name=XDAQ Software worksuite
baseurl=http://xdaq.web.cern.ch/xdaq/repo/worksuite/15/cc7/x86_64/RPMS/
enabled=1
gpgcheck=0
[xdaq-updates]
name=XDAQ Software xaas
baseurl=http://xdaq.web.cern.ch/xdaq/repo/xaas/15/cc7/x86_64/RPMS/
enabled=1
gpgcheck=0
EOF
sudo cat > /etc/yum.repos.d/amc13-sw.repo <<EOF
[cactus-amc13-base]
name=CACTUS Project Software Repository for amc13 packages
baseurl=http://cactus.web.cern.ch/cactus/release/amc13/1.2/centos7_x86_64/base/RPMS
enabled=1
gpgcheck=0
EOF
sudo cat > /etc/yum.repos.d/ipbus-sw.repo <<EOF
[ipbus-sw-base]
name=IPbus software repository
baseurl=http://www.cern.ch/ipbus/sw/release/2.6/repos/centos7_x86_64/base/RPMS
enabled=1
gpgcheck=0
[ipbus-sw-updates]
name=IPbus software repository updates
baseurl=http://www.cern.ch/ipbus/sw/release/2.6/repos/centos7_x86_64/updates/RPMS
enabled=1
gpgcheck=0
EOF

Install cactus

sudo yum install cactusboards-amc13-tools-1.2.14-0.centos7 cactusboards-amc13-  amc13-1.2.14-0.centos7
sudo yum install cactuscore-uhal-grammars cactuscore-uhal-uhal cactuscore-uhal-tests   cactuscore-uhal-pycohal cactuscore-uhal-gui cactuscore-uhal-tools cactuscore-controlhub cactusboards-amc13-amc13 cactusboards-amc13-tools pugixml-devel

Install XDAQ

sudo yum group install cmsos_core cmsos_worksuite --skip-broken

Other packages

sudo yum install e2fsprogs-devel libuuid-devel curlpp curlpp-devel.x86_64 freetype freetype-devel xorg-x11-fonts-75dpi libuuid-devel libcurl-devel  pugixml-devel boost boost-devel

Download POS and set environment

mkdir TriDAS_lea
cd TriDAS_lea
scl enable devtoolset-8 bash
git clone https://gitlab.cern.ch/cmspops/pos.git pixel
cd pixel
git checkout master     
cd ..
cp pixel/POSRelease/setenv.sh .
cat > local.sh <<EOF
export ROOTSYS=/home/cmspixel_centos7/internalhdd/ROOT/install
export BUILD_HOME=/home/cmspixel_centos7/internalhdd/TriDAS_lea
export POS_INSTALL_PATH=\$BUILD_HOME/local
export POS_OUTPUT_DIRS=\$BUILD_HOME/pixel/PixelRun/Runs
export POS_LOG_DIR=\$BUILD_HOME/pixel/PixelRun/Logs
export PIXELCONFIGURATIONBASE=\$BUILD_HOME/Config
EOF
source setenv.sh

Download and compile FecSoftware

git clone https://gitlab.cern.ch/cmspos/FecSoftware.git FecSoftwareV3_0
cd FecSoftwareV3_0
make -j 8
make install

Compile POS

cd $BUILD_HOME/pixel
make Set=pixel -j 8
make install
cd $BUILD_HOME/pixel/PixelRun
mkdir Logs Runs

Note: I encountered compilation errors and had to add the line:

#include <TSystem.h>

to these two header files:

TriDAS_lea/pixel/PixelUtilities/PixelRootUtilities/include/PixelHistoThreadFrame.h
TriDAS_lea/pixel/PixelUtilities/PixelRootUtilities/include/PixelHistoThreadFrameWithArgs.h