Installing ROOT6

In order to install ROOT6, one must first upgrade the gcc compiler, and also install Python 2.7

Step 1: Upgrade gcc compiler to version 4.9.2

First, become superuser, and then:

yum update
wget http://people.centos.org/tru/devtools-3/devtools-3.repo -O /etc/yum.repos.d/devtools-3.repo
yum install devtoolset-3-gcc devtoolset-3-binutils
yum install devtoolset-3-gcc-c++ devtoolset-3-gcc-gfortran

Exit the superuser shell. In a regular terminal window, in order to switch to using the new compiler version, one must execute the following:

scl enable devtoolset-3 bash
source /opt/rh/devtoolset-3/enable

One can then check that the new version of the compiler is being used with:

gcc --version

Step 2: Upgrade to Python 2.7.14

Again, become superuser, and then execute the following:

cd /usr/src
wget https://www.python.org/ftp/python/2.7.14/Python-2.7.14.tgz
tar xzf Python-2.7.14.tgz
cd Python-2.7.14
./configure --enable-shared
make altinstall

This will install the new version of Python in /usr/local/bin/python2.7

One needs to make a soft link in /usr/local/bin in order that the ROOT configure script picks up the new version:

cd /usr/local/bin
ln -sf python2.7 python
ln -sf python2.7-config python-config

The final state is to add /usr/local/lib to /etc/ld.so.conf and then run:

ldconfig

Exit superuser mode.

Step 3: Download and compile ROOT6

From a terminal window, in the home directory of the local user that you created, do:

mkdir root6
cd root6
git clone http://root.cern.ch/git/root.git

Note that downloading the source could take several minutes. Once downloaded, there should be a new "root" directory under the newly created root6 directory. Now, do:

cd root
mkdir obj
cd obj
cmake ..
make -j 4
sudo make install