AliRoot

ROOT

2025-10

• https://root-forum.cern.ch/t/classdef-classimp/45679 (2021-07)

ClassImp is not needed since many many years. ClassDef is required for classes inheriting from TObject, and an optional I/O optimization for another classes.

• https://github.com/root-project/web/pull/611
• https://github.com/root-project/web/pull/612
• https://github.com/eguiraud/root_dictionaries_tutorial/ (2021-05)
• https://root.cern/manual/io_custom_classes/#the-classdef-macro FINAL

return Form("x=%g, y=%g", x, y);
return Form("TGLSceneBase %s", fName.Data());
// inside a thread-local static character buffer

XRootD

cmake ../xrootd-4.8.1/ -DCMAKE_INSTALL_PREFIX=/cern/xrootd-4.8.1
make; make install
cd /cern; ln -s xrootd-4.8.1 xrootd

XRootD cannot be built in-source! Please run cmake <src-dir> outside the source directory and be sure to remove CMakeCache.txt or CMakeFiles if they exist in the source directory.

ROOT

 // ROOT 6.26 C++14 (2022-04 => 2024-03)
 // ROOT 6.28 C++14 (2023-02 => 2024-01)
 // ROOT 6.30 C++17 (2023-11 => 2024-01)
 // ROOT 6.32 C++17 (2024-05 => actual)

• https://root.cern.ch/building-root
• https://github.com/root-project/web/blob/main/install/build_from_source.md
• https://github.com/root-project/root-docker

• install in /cern/root_master (source dir) and build in /cern/root_master_build (out of source dir)
• it is not supported to build ROOT on the source directory
• location independent installation method
• by default CMAKE_INSTALL_PREFIX=/usr/local
• don't try CMAKE_INSTALL_PREFIX=. (install files and up-to-date files => make install and make loop)

• Before trying to build ROOT, see the “Build Prerequisites” web page. In any case, when you are building a new ROOT version, make always sure that nothing in your environment variables (i.e. “ROOTSYS”, “PATH”, “LD_LIBRARY_PATH”) points to another existing version of ROOT (and that’s another good reason why there should be no ROOT related files in “standard” system locations, like “/usr/[bin|lib]” or “/usr/local/[bin|lib]”). [1]

• https://sft.its.cern.ch/jira/browse/ROOT-9309
  • it's better to never set ROOTSYS, PATH and LD_LIBRARY_PATH and never source thisroot.sh
  • https://github.com/root-project/root/commit/4e4e1d00d9a639969725069b6c7b4ebbcd875303
• https://root-forum.cern.ch/t/pyroot-experimental-not-working-in-6-20-06/40059/8
• recommended method

$ export | grep root
declare -x LD_LIBRARY_PATH="/cern/xrootd/lib64"
declare -x PATH=" :/cern/root/bin:/cern/xrootd/bin: "

cd /cern
git clone --depth 1 http://root.cern.ch/git/root.git root_master_source
git clone --depth 1 http://root.cern.ch/git/root.git root_master
git clone --branch master --depth 1 https://github.com/root-project/root.git root_master_src

ln -s root_master root     # PATH="/cern/root/bin"
mkdir root_master_build/
cd root_master_build

cmake /cern/root_master_src/ -Droofit=OFF -Dtmva=OFF -Dmathmore=OFF -DXROOTD_ROOT_DIR=/cern/xrootd/ -DCMAKE_INSTALL_PREFIX=/cern/root_master/ -Drpath=ON
cmake /cern/root_master_source/ -Droofit=OFF -Dtmva=OFF -Dmathmore=OFF -Dhttp=ON -DXROOTD_ROOT_DIR=/cern/xrootd/ -DCMAKE_INSTALL_PREFIX=/cern/root_master/ -Drpath=ON -DCMAKE_CXX_STANDARD=17 -Droot7=ON
# -Dfortran=ON (needed for h2root and g2root)
cmake /cern/root_master -Droofit=OFF -Dtmva=OFF -Dmathmore=OFF -Dhttp=ON -DXROOTD_ROOT_DIR=/cern/xrootd -DCMAKE_INSTALL_PREFIX=/cern/root_master -Drpath=ON
make
make install

• old method

$ export | grep root
declare -x LD_LIBRARY_PATH="/cern/root/lib:/cern/xrootd/lib64"
declare -x PATH=" :/cern/root/bin:/cern/xrootd/bin: "
declare -x ROOTSYS="/cern/root"

cd /cern
git clone --depth 1 http://root.cern.ch/git/root.git root_master
ln -s root_master root     # ROOTSYS="/cern/root"
mkdir root_master_build/
cd root_master_build/
cmake /cern/root_master -Droofit=OFF -Dtmva=OFF -Dmathmore=OFF -Dhttp=ON -DXROOTD_ROOT_DIR=/cern/xrootd -DCMAKE_INSTALL_PREFIX=/cern/root_master
make
make install

• update

cd /cern/root_master_build
git -C /cern/root_master pull
rm /cern/root_master/etc/dictpch/allLinkDefs.h /cern/root_master/etc/allDict.cxx.pch /cern/root_master/etc/dictpch/allHeaders.h /cern/root_master/tutorials/hsimple.root
make
make install

• to start from a clean configuration it is recommended to delete the file root_master_build/CMakeCache.txt
• You can inspect the list of options and their descriptions by running cmake -LH $PWD in the build directory
• Allow to build ROOT without any Internet connection https://sft.its.cern.ch/jira/browse/ROOT-9163
• CMakeFiles/move_artifacts.dir/build.make find removed file(s)
• for building clang-format from ROOT LLVM/Clang source code add CMake variable -DCLANG_ENABLE_FORMAT=ON

make   # build LibFormat library
cd /cern/root_master_build/interpreter/llvm/src/tools/clang/tools/clang-format
make   # build ClangFormat stand-alone tool