Question

A workflow on the ubuntu-latest GitHub-hosted runner uses actions/setup-python to select Python 3.12. The build previously completed in about 30 seconds during setup, but after a recent runner image update the setup step now takes several minutes and logs show it is downloading and building the interpreter instead of reading from the local cache. The team wants setup to return to using the fast preinstalled interpreter without changing which minor version they target. What is the most likely cause and appropriate fix?

Accepted Answer

The requested version is no longer present in the runner's toolcache for that image; pin to a Python version that the image release notes list as preinstalled (or accept the runtime download).

Answer

The setup-python action version is out of date; upgrading the action major version will force it to always read from the toolcache regardless of image contents.

Answer

Caching is disabled by default; adding actions/cache keyed on the Python version will make setup-python restore the interpreter from the toolcache.

Answer

The runner ran out of disk space, so the toolcache was evicted; adding a cleanup step to free space will restore the preinstalled interpreter.