# The error `env.device`

**environment**: something the run needs is missing or different where it runs (a package, a file, a device, the network): the error names what to install, fetch or attach.

Where MIME gives it, with what its message says happened and what its action says to do (`{…}` is filled in from the experiment):

- in `mime/env/_check.py`:
  - what happened: `the run requested the CPU and JAX computes on {…}`
  - what to do: `request the GPU the run uses, or hide it from JAX (JAX_PLATFORMS=cpu)`
- in `mime/env/_check.py`:
  - what happened: `the run requested a {…} and JAX sees {…}{…}`
  - what to do: `run where JAX sees a {…}: attach the GPU, and install the cuda12 pins ('mime env check --variant cuda12')`

Reading an error and reaching its full traceback: [reading an error](../reading_errors.md). Every code: [the index](index.md).