GitHub Actions Pipeline Failure Masked - pipefail Not Set in run:
A step reports success even though a command in a pipeline failed, because only the last command's exit status counts unless pipefail is set. Overriding the shell, or piping to tee, can drop the default safety and mask real failures.
What this error means
A run step ends green while an earlier command in a pipe (a build, a test, a generator) actually failed, because the pipeline's exit status came from the last stage (often tee or grep), not the failing command.
- run: ./run-tests.sh | tee results.log
shell: sh # custom shell drops the default bash pipefail
# tests fail, but tee exits 0, so the step passesCommon causes
A custom shell removes the default flags
GitHub runs bash steps with set -eo pipefail by default. Specifying shell: sh (or a custom shell line) replaces those defaults, so a failing piped command is no longer caught.
Last-stage exit status wins
Without pipefail, a pipeline reports the exit code of its last command. Piping a failing command to tee, grep, or sort hides the upstream failure.
How to fix it
Keep or restore pipefail
Use the default bash shell, or set the flags yourself when overriding the shell.
- run: |
set -eo pipefail
./run-tests.sh | tee results.logSet defaults at the job level
- Add defaults.run.shell: bash so steps keep pipefail without per-step overrides.
- When a step truly needs sh, add set -e and check ${PIPESTATUS[0]} or restructure to avoid masking.
- Avoid ending a pipeline with a command that always exits 0 unless you have checked the upstream status.
How to prevent it
- Keep the default bash shell so pipefail stays on.
- When overriding shell:, re-add set -eo pipefail explicitly.
- Avoid piping failing commands into tee/grep without checking PIPESTATUS.