Installing ROOT on Debian Stable (stretch)

I find the official general instructions for building and installing ROOT annoyingly unclear and ambiguous, so this post describes how to perform installation of a so-called "Location Independent" (i.e., non-system-wide) build of CERN's ROOT package on Debian stretch. I assume that cmake is already installed, and that you're using bash or something similar as a shell.

Download Source

1. Create (if necessary) and go to a clean directory
2. Determine the version of ROOT that you want to download (see, for example, https://root.cern.ch/downloading-root).
3. For example, as I write this, the "production" version is 6.16.00
4. Download this by a command of the form:
  wget https://root.cern.ch/download/root_vn.nn.nn.source.tar.gz

In my case, I therefore executed:
   wget https://root.cern.ch/download/root_v6.16.00.source.tar.gz

Extract the source tree:
  tar -zxf root_v6.16.00.source.tar.gz

Build ROOT

Make a subdirectory that will eventually serve as the root of the ROOT hierarchy. [Yes, "ROOT" is an unnecessarily confusing name for this software.] Assuming I call this directory ROOTroot, then:

  mkdir ROOTroot
  cd ROOTroot
  cmake ../root-6.16.00
  cmake --build

Do other stuff for a couple of hours or so, because buliding ROOT takes a long time. When the build has completed, a complete hierarchy based at ROOTroot should have been built. On my system, that hierarchy runs to about 3.1 GB.

Prepare your shell for executing ROOT

Now execute:

  . bin/thisroot.sh

Test ROOT

Now you should be able to execute ROOT simply by typing:

  root

Move the ROOT tree if necessary

The entire hierarchy based at ROOTroot may be copied or moved somewhere more convenient if you decide that you've built ROOT somewhere other than where you want it to reside. For example, suppose we want ROOT to be in ~/ROOT, then we execute:

  cp -r . ~/ROOT

to copy the entire ~3GB hierarchy. Then, to use ROOT, we dot-execute the script thisroot.sh in the bin directory under the new root(!) of the hierarchy. So, for example:

. ~/ROOT/bin/thisroot.sh

After this, ROOT may be started simply executing:

  root

Access ROOT easily from subsequent sessions

In order to make ROOT easily available simply by typing

  root

in subsequent sessions, you may want to add the command:

    . ~/ROOT/bin/thisroot.sh
   
to your ~/.bashrc file, or its equivalent for your bash-like shell.