What Is RUNNER_OS?

RUNNER_OS is the operating system of the runner executing the job - Linux, Windows, or macOS.

RUNNER_OS is essential in matrix builds that run across operating systems, letting steps choose OS-specific commands or cache paths.

Example

Pick a cache path per OS.

yaml

if: ${{ runner.os == 'Windows' }}

Cost note

macOS runners cost roughly 10x Linux and Windows about 2x. Keep cross-OS matrices lean, and run the heavy Linux legs on cheaper managed runners like Latchkey.

Key takeaways

RUNNER_OS is Linux, Windows, or macOS.
Key for cross-OS matrix builds.
macOS/Windows minutes cost far more than Linux.

Related guides

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