(setting-up-root)=
# Walkthrough: Setting up ROOT 
**(5 minutes)**

Before you start using ROOT, you usually have to set it up:

   - If you're not using one of the Nevis particle-physics systems, hopefully
     you have received instructions on how to set up ROOT at your site. Now
     is the time to follow those directions.

   - If you had to {ref}`install ROOT <installing>` on your own 
     you already know whatever special set-up you need on your local
     computer.

   - If you are using one of the particle-physics systems at Nevis, type:

         > module load root

:::::{admonition} Nevis specifics
:class: note

The command `module load root`[^f14] sets some Unix environment
variables and modifies your command and library paths. If you need to
remove these changes, use the command `module unload root`.

[^f14]: The `module load` UNIX command is part of a package called
    "environment modules." Though it's a standard package, environment
    modules are not normally included in a default UNIX installation.
    Here's a [Nevis wiki page on available modules](https://twiki.nevis.columbia.edu/twiki/bin/view/Main/EnvironmentModules). 

One of the variables that's set is \$ROOTSYS. This will be helpful to
you if you're following one of the examples in the [ROOT Users
Guide](https://root.cern/root/htmldoc/guides/users-guide/ROOTUsersGuide.html).
If you're told to find a file in \$ROOTSYS/tutorials (see
the {ref}`references` section of this tutorial, for example) you'll be able
to do this only after you've typed `module load root.`

You have to execute `module load root` once each time you login to
Linux and use ROOT. If you wish this command to be automatically
executed when you login, you can add it to the .`myprofile` file in
your home directory (but read the warnings below before you do this).

:::{warning}

-   It's a Nevis convention to use `~/.myprofile` for your custom
    shell setup. Other sites may tell you to edit `~/.profile`,
    `~/.bashrc`, `~/.bash_profile`, `~/.zprofile`,
    `~/.cshrc`, `~/.tcshrc`, etc. There is a Nevis wiki page on
    [shell setup scripts](https://twiki.nevis.columbia.edu/twiki/bin/view/Main/Shell).

-   Even at Nevis, some physics groups work with software frameworks
    that have their own versions of ROOT built-in; e.g., Athena in ATLAS
    or LArSoft in MicroBooNE. If you're working with such a framework,
    you'll have a special set-up command to use; you must *not* use the
    generic Nevis `module load root`.

-   Finally, do not put `module load root` in a start-up script if
    you're using the {ref}`Nevis notebook server <the notebook server>`.
    You'll get lots of "not found" errors.
:::
:::::