Standalone ROOT

The currently recommended way of accessing stand-alone ROOT is through the CVMFS filesystem. (All clusters mount it under /cvmfs)

There are multiple versions of ROOT available, compiled against various C++ compilers to match various needs.

Please, have a look under  

/cvmfs/sft.cern.ch/lcg/app/releases/ROOT

Here is a brief recipe for setting up stand-alone ROOT v6.06.04 for gcc 4.9.1 environment:

source /cvmfs/sft.cern.ch/lcg/external/gcc/4.9.1/x86_64-slc6-gcc48-opt/setup.sh
source /cvmfs/sft.cern.ch/lcg/app/releases/ROOT/6.06.04/x86_64-slc6-gcc49-opt/root/bin/thisroot.sh

Test: 

which root
/cvmfs/sft.cern.ch/lcg/app/releases/ROOT/6.06.04/x86_64-slc6-gcc49-opt/root/bin/root

If a different version of ROOT or GCC is needed - these can be changed in accordingly. Please, check carefully what combinations exist in CVMFS

Also,  be reminded that ROOT can be setup for a specific CMSSW environment by following the usual setup procedure:

export VO_CMS_SW_DIR=/cvmfs/cms.cern.ch
source $VO_CMS_SW_DIR/cmsset_default.sh
export SCRAM_ARCH=slc6_amd64_gcc530
/cvmfs/cms.cern.ch/slc6_amd64_gcc530/cms/cmssw/CMSSW_9_0_0/src/
cmsenv
cd -  

Test:

which root 
/cvmfs/cms.cern.ch/slc6_amd64_gcc530/cms/cmssw/CMSSW_9_0_0/external/slc6_amd64_gcc530/bin/root

Again - different versions of SCRAM_ARCH  and CMSSW release can be selected, depending on needs.