GitHub Actions exit code 137 usually means the kernel killed a step for running out of memory

Exit code 137 corresponds to signal 9 (SIGKILL), typically sent by the Linux out-of-memory killer on a CI runner rather than by a failure in the code itself. The step stops abruptly with no stack trace or error message explaining the cause, and retrying it generally fails again because the memory limit remains unchanged. The problem can appear intermittently, depending on what else ran on the machine beforehand, and a container killed for exceeding its --memory cap reports the same code. Other possible causes include a deliberate SIGKILL from a timeout wrapper or raising a heap limit above the runner's RAM. The fix is to confirm the kill through the kernel log, then reduce peak memory use or move the job to a larger runner.