bpo-35537: use os.posix_spawn in subprocess by nanjekyejoannah · Pull Request #11242 · python/cpython

I expect that posix_spawn() sets errno as does execv()

As I explained, this behavior is not required by POSIX, and the opposite behavior is allowed. Recent glibc- and musl-based Linux behave as you expect, but for glibc, this was added in 2017. In my test on Ubuntu 14.04, ./python -c "import subprocess; subprocess.call(['/xxx'], close_fds=False, restore_signals=False)" silently returns with zero exit code.

FreeBSD also seems not to use any synchronous notification.

Other systems where posix_spawn is a syscall (macOS?) probably behave as you expect, but I've not checked.