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Efficient analysis with ROOT

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Get ROOT

Overview

Teaching: 10 min
Exercises: 5 min
Questions

  • How to install ROOT on my system or get access to systems with ROOT pre-installed?

Objectives

  • Find the most efficient way for you to get access to ROOT

  • Install ROOT or connect to a machine with ROOT already installed

This section shows you multiple ways to get ROOT. Find below solutions to run ROOT locally, on LXPLUS, in batch systems and CIs!

Conda

Conda is a package management system and environment management system, which can install ROOT in a few minutes on Linux and MacOS.

The fastes way to get ROOT is installing Miniconda (a minimal Conda installation) and then run the following two commands:

conda create -c conda-forge --name <my-environment> root
conda activate <my-environment>

You can find detailed information about ROOT on Conda in this blog post.

CVMFS

CVMFS is a software distribution service that is already set up on many HEP systems. CMSSW including ROOT is distributed via CVMFS, but also other software stacks are available that contain ROOT.

Most notably, the CERN service LXPLUS has CVMFS always installed and enables rapid access to software and computing resources.

CMSSW

The following commands let you find out quickly which ROOT version comes with CMSSW.

# Source setup tools
source /cvmfs/cms.cern.ch/cmsset_default.sh

# Show CMSSW versions
scram list

# Setup CMSSW environment (using CMSSW_11_1_3 here)
cmsrel CMSSW_11_1_3
cd CMSSW_11_1_3/

# Show information about ROOT
scram tool list | grep root

# Source this CMSSW release
cmsenv

LCG

Another option to get ROOT via CVMFS are the LCG releases. All information about the releases and contained packages can be found at http://lcginfo.cern.ch. Most releases are available as a Python 2 and Python 3 version, for example 98 and 98python3. There are also development releases every night, which contain the latest ROOT release in dev4 and the very latest developments from ROOT master in dev3.

The following example shows you how to source LCG 98 based on Python 3 on a CentOS 7 machine such as those on LXPLUS. Note the platform and compiler dependent information in the path, which have to be adjusted based on your system. The available combinations are shown on the website.

source /cvmfs/sft.cern.ch/lcg/views/LCG_98python3/x86_64-centos7-gcc10-opt/setup.sh

Docker

If you want to use ROOT in a CI system (e.g. GitLab pipelines or GitHub actions), most likely the software will be made available via Docker. The official ROOT docker containers can be found at https://hub.docker.com/r/rootproject/root. The different base images and ROOT versions are encoded in the tags, for example 6.22.00-ubuntu20.04, and latest will get you the latest ROOT release (v6.22) based on Ubuntu 20.04. If you want to try it, get Docker and run the following command to start the container with a bash shell.

docker run --rm -it rootproject/root /bin/bash

Binary releases and packages

The classic way to distribute software, besides the source code, are plain binary releases. You can download these from the release pages on https://root.cern/install/all_releases for all major MacOS and Linux versions. If you choose this installation method, make sure ROOT dependencies are installed on your system. Complete installation instructions for binary releases are available here.

In addition, for some Linux distributions, the ROOT community maintains packages in the respective package managers. You can find a list of maintained packages at https://root.cern/install/#linux-package-managers.

Verify the ROOT version

Since ROOT has a long history and numerous releases, on old systems such Scientific Linux 6 you may find correspondingly old ROOT versions. However, with the following commands you can easily verify your ROOT version and also find expert details about the ROOT configuration!

# ROOT version and build tag
root --version

# Again the ROOT version (this also works with older ROOT versions)
root-config --version

# Check that ROOT was built with C++14 support
# The output must contain one of -std=c++{14,17,1z} so that all code examples of this lesson run!
root-config --cflags

# List all the ROOT configuration options that can be checked
root-config --help

Find your way to access ROOT!

For the exercises later you need at least ROOT 6.18 and C++14 support. Feel free to set up for yourself your preferred environment satisfying this requirement!

Fallback solution

As a fallback solution you can always connect to LXPLUS via ssh -Y your_username@lxplus.cern.ch. The -Y flag enables X forwarding, which allows you to forward the output of graphics application in case you run a system with an X server such as almost all Linux distributions.

Key Points

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