Frequently Asked Questions#

What is the relationship between conda-rattler-solver, rattler, resolvo, and pixi?#

resolvo is a dependency solver written in Rust. rattler is a Rust library for working with the conda ecosystem, and it uses resolvo to solve conda environments. pixi is a package manager built on top of rattler. conda-rattler-solver uses the Python bindings for rattler, py-rattler, to make that same solver available inside conda through its solver plugin interface.

How do I check which solver is in use?#

Run:

$ conda config --show solver

If the output is solver: rattler, conda-rattler-solver is the default solver. To see where the setting comes from, use conda config --show-sources.

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

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

$ conda config --set solver rattler

To undo this change, run:

$ conda config --remove-key solver

I get an error when I pass `--solver=rattler`#

If you see an error such as:

CondaValueError: Invalid choice for 'solver': rattler

the plugin is not installed in the environment that provides the conda command, which is usually base. Install it there, not in the environment you are trying to modify:

$ conda install -n base conda-rattler-solver

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!

If you configured it as the default solver, revert it first:
```
$ conda config --remove-key solver
```

Then, remove the package from base:

$ conda remove -n base conda-rattler-solver

Why does the solver pick a different solution than classic or libmamba?#

All three solvers are correct, but they do not always agree when several solutions satisfy the request. The underlying algorithms, and the order in which they consider candidates, differ. Being more explicit about what you want, for example, conda install python=3.13 numpy instead of conda install numpy, narrows the solution space and usually gets you the solution you expected. See Known limitations and differences for known differences.

Where can I report a bug or ask for help?#

Please file an issue in the conda-rattler-solver repository. For general questions, the conda Zulip is a good place to ask.