Frequently Asked Questions#

What’s the difference between the available solvers in conda?#

Please refer to the section “Technical differences between libmamba and classic” in the libmamba-vs-classic docs.

How do I uninstall it?#

If you don’t want to use the solver anymore, follow these instructions:

Warning

Please make sure you follow all steps below to uninstall the solver!

  1. If you configured it as the default solver, make sure you revert it with:

    $ conda config --remove-key solver
# You might also need this:
$ conda config --remove-key experimental_solver

  2. Then, remove the package from base with:

    $ conda remove -n base conda-libmamba-solver

How do I configure conda to use the solver permanently?#

Use the following command to always use libmamba as your default solver:

$ conda config --set solver libmamba

To undo this change permanently, run:

$ conda config --remove-key solver
# You might also need this:
$ conda config --remove-key experimental_solver

I get an error when I try to use the --solver flag#

If you are seeing this error:

CondaValueError: Key 'solver' is not a known primitive parameter.

It might mean you are using an old version of the conda-libmamba-solver package. You can check which version is installed with conda list -n base conda-libmamba-solver.

Before version 22.12, the CLI flag was --experimental-solver. We recommend you upgrade to conda 22.11 or above, and then conda-libmamba-solver 22.12 or above.

See the 22.12.0 announcement post for more details on how to upgrade.

I have an older conda and I can’t install conda-libmamba-solver#

Since older conda versions only supported the classic solver, you might run into solver conflicts or too long installations if your base environment is too constrained. This becomes a “chicken-and-egg” problem where you’d need conda-libmamba-solver to update to a more recent conda with conda-libmamba-solver.

Fortunately, there’s a workaround thanks to the conda-standalone project. This is a single binary that bundles recent conda versions, with conda-libmamba-solver included. It’s not a substitute for the full conda user experience but it can help bootstrap and rescue conda installations.

  1. Download the most recent conda-standalone from its Github Releases page. Make sure to pick the one for your operating system and platform. Once downloaded, rename it as conda.exe on Windows and conda on Linux / macOS.

  2. Write down the location of your base environment: conda info --root.

  3. Write down the main preconfigured channel in your installation: conda config --show channels. This is usually defaults or conda-forge.

  4. Go to the Downloads directory and run this command from your terminal:

On Windows:

.\conda.exe install -p "[path given by step 2]" -c [channel from step 3] "conda>=23.10" conda-libmamba-solver

On Linux or macOS:

./conda install -p "[path given by step 2]" -c [channel from step 3] "conda>=23.10" conda-libmamba-solver

Once the command succeeds, you’ll have conda-libmamba-solver installed in your base environment and will be ready to use it as normal. You can delete the conda-standalone binaries.