Conda Basics


This guide introduces a user to the basic workflow of using conda environments, as well as providing an example of how to create a conda environment that uses a different version of Python than the base environment uses on Summit. Although Summit is being used in this guide, all of the concepts still apply to other OLCF systems.

OLCF Systems this guide applies to:

  • Summit

  • Andes

  • Frontier

Inspecting and setting up an environment

First, load the python module and the gnu compiler module (most Python packages assume use of GCC)

$ module load gcc/12.1.0
$ module load python/3.10-miniforge3
$ module load gcc/9.3.0
$ module load python
$ module load PrgEnv-gnu/8.3.3
$ module load python/3.10-miniforge3

This puts you in the “base” conda environment, which is the default Python environment after loading the module. To see a list of environments, use the command conda env list:

$ conda env list

# conda environments:
base                  *  /sw/summit/python/3.10/miniforge3/23.11.0

This also is a great way to keep track of the locations and names of all other environments that have been created. The current environment is indicated by *.

To see what packages are installed in the active environment, use conda list:

$ conda list

# packages in environment at /sw/summit/python/3.10/miniforge3/23.11.0:
# Name                    Version                   Build  Channel
_libgcc_mutex             0.1                 conda_forge    conda-forge
_openmp_mutex             4.5                       2_gnu    conda-forge
archspec                  0.2.2              pyhd8ed1ab_0    conda-forge
boltons                   23.1.1             pyhd8ed1ab_0    conda-forge
brotli-python             1.1.0           py310hc6cd4ac_1    conda-forge
bzip2                     1.0.8                hd590300_5    conda-forge
c-ares                    1.24.0               hd590300_0    conda-forge
ca-certificates           2023.11.17           hbcca054_0    conda-forge
certifi                   2023.11.17         pyhd8ed1ab_0    conda-forge

You can find the version of Python that exists in this base environment by executing:

$ python3 --version

Python 3.10.13


Although the base environment is 3.10.13, you are NOT limited to this version in any subsequent conda environments. I.e., you can install other Python versions in new conda environments.

Creating a new environment

For this guide, you are going to install a different version of Python.

To do so, create a new environment using the conda create command. As an example, let’s create an environment in the NFS “project home” space:

$ conda create -p /ccs/proj/<project_id>/<username>/envs/summit/py311-summit python=3.11.0

The -p flag specifies the desired path and name of your new virtual environment. The directory structure is case sensitive, so be sure to insert <project_id> as lowercase. Directories will be created if they do not exist already (provided you have write-access in that location). Instead, one can solely use the --name <your_env_name> flag which will automatically use your $HOME directory.

After executing the conda create command, you will be prompted to install “the following NEW packages” – type “y” then hit Enter/Return. Downloads of the fresh packages will start and eventually you should see something similar to:

Preparing transaction: done
Verifying transaction: done
Executing transaction: done
# To activate this environment, use
#     $ conda activate /ccs/proj/<project_id>/<username>/envs/summit/py311-summit
# To deactivate an active environment, use
#     $ conda deactivate

Due to the specific nature of conda on Summit, you must use source activate and source deactivate instead of conda activate and conda deactivate. Let’s activate the new environment:

$ source activate /ccs/proj/<project_id>/<username>/envs/summit/py311-summit

The path to the environment should now be displayed in “( )” at the beginning of your terminal lines, which indicate that you are currently using that specific conda environment. And if you check with conda env list again, you should see that the * marker has moved to your newly activated environment:

$ conda env list

# conda environments:
                      *  /ccs/proj/<project_id>/<username>/envs/summit/py311-summit
base                     /sw/summit/python/3.8/anaconda3/2020.07-rhel8

Installing packages

Next, let’s install a package (NumPy). There are a few different approaches.

Installing with pip

One way to install packages into your conda environment is to build packages from source using pip. This approach is useful if a specific package or package version is not available in the conda repository, or if the pre-compiled binaries don’t work on the HPC resources (which is common). However, building from source means you need to take care of some of the dependencies yourself, especially for optimization. Pip is available to use after installing Python into your conda environment, which you have already done.


Because issues can arise when using conda and pip together (see link in Additional Resources), it is recommended to do this only if absolutely necessary.

To build a package from source, use pip install --no-binary=<package_name> <package_name>:

$ CC=gcc pip install --no-binary=numpy numpy

The CC=gcc flag will ensure that you are using the proper compiler and wrapper. Building from source results in a longer installation time for packages, so you may need to wait a few minutes for the install to finish.

You have successfully built NumPy from source in your conda environment; however, you did not link in any additional linear algebra packages, so this version of NumPy is not optimized. Let’s install a more optimized version using a different method instead, but first you must uninstall the pip-installed NumPy:

$ pip uninstall numpy

Installing with conda commands

The traditional, and more basic, approach to installing/uninstalling packages into a conda environment is to use the commands conda install and conda remove. Let’s do this to install NumPy:

$ conda install numpy

Because NumPy depends on other packages for optimization, this will also install all of its dependencies. You have just installed an optimized version of NumPy, now let’s test it.

Testing your new environment

Let’s run a test to make sure everything installed properly. Since you are running a small test, you can do this without having to run on a compute node.


Remember, at larger scales both your performance and your fellow users’ performance will suffer if you do not run on the compute nodes. It is always highly recommended to run on the compute nodes (through the use of a batch job or interactive batch job).

Make sure you’re in a Python shell first, then print out the versions of Python and NumPy:

$ python3
>>> import platform
>>> import numpy
>>> py_vers = platform.python_version()
>>> np_vers = numpy.__version__
>>> print("Hello from Python", py_vers)
Hello from Python 3.11.0
>>> print("You are using NumPy", np_vers)
You are using NumPy 1.26.4

Additional Tips

  • Cloning the base environment:

    It is not recommended to try to install new packages into the base environment. Instead, you can clone the base environment for yourself and install packages into the clone. To clone an environment, you must use the --clone <env_to_clone> flag when creating a new conda environment. An example for cloning the base environment into your Project Home directory on Summit is provided below:

    $ conda create -p /ccs/proj/<YOUR_PROJECT_ID>/<YOUR_USER_ID>/envs/summit/baseclone-summit --clone base
    $ source activate /ccs/proj/<YOUR_PROJECT_ID>/<YOUR_USER_ID>/envs/summit/baseclone-summit
  • Adding known environment locations:

    For a conda environment to be callable by a “name”, it must be installed in one of the envs_dirs directories. The list of known directories can be seen by executing:

    $ conda config --show envs_dirs

    On OLCF systems, the default location is your $HOME directory. If you plan to frequently create environments in a different location other than the default (such as /ccs/proj/...), then there is an option to add directories to the envs_dirs list.

    For example, to track conda environments in a subdirectory called summit in Project Home you would execute:

    $ conda config --append envs_dirs /ccs/proj/<YOUR_PROJECT_ID>/<YOUR_USER_ID>/envs/summit

    This will create a .condarc file in your $HOME directory if you do not have one already, which will now contain this new envs_dirs location. This will now enable you to use the --name env_name flag when using conda commands for environments stored in the summit directory, instead of having to use the -p /ccs/proj/<YOUR_PROJECT_ID>/<YOUR_USER_ID>/envs/summit/env_name flag and specifying the full path to the environment. For example, you can do source activate py3711-summit instead of source activate /ccs/proj/<YOUR_PROJECT_ID>/<YOUR_USER_ID>/envs/summit/py3711-summit.

  • Exporting (sharing) an environment:

    You may want to share your environment with someone else. One way to do this is by creating your environment in a shared location where other users can access it. A different way (the method described below) is to export a list of all the packages and versions of your environment (an environment.yml file). If a different user provides conda the list you made, conda will install all the same package versions and recreate your environment for them – essentially “sharing” your environment. To export your environment list:

    $ source activate my_env
    $ conda env export > environment.yml

    You can then email or otherwise provide the environment.yml file to the desired person. The person would then be able to create the environment like so:

    $ conda env create -f environment.yml

Quick-Reference Commands

  • List environments:

    $ conda env list
  • List installed packages in current environment:

    $ conda list
  • Creating an environment with Python version X.Y:

    For a specific path:

    $ conda create -p /path/to/your/my_env python=X.Y

    For a specific name:

    $ conda create -n my_env python=X.Y
  • Deleting an environment:

    For a specific path:

    $ conda env remove -p /path/to/your/my_env

    For a specific name:

    $ conda env remove -n my_env
  • Copying an environment:

    For a specific path:

    $ conda create -p /path/to/new_env --clone old_env

    For a specific name:

    $ conda create -n new_env --clone old_env
  • Activating/Deactivating an environment:

    $ source activate my_env
    $ source deactivate # deactivates the current environment
  • Installing/Uninstalling packages:

    Using conda:

    $ conda install package_name
    $ conda remove package_name

    Using pip:

    $ pip install package_name
    $ pip uninstall package_name
    $ pip install --no-binary=package_name package_name # builds from source

Additional Resources