yeah, unfortunately, despite literally being specified in posix (hell, macos bundles it)
one of these days i will go around pestering distro release engineers to include it; after all, it's less heavyweight than any one of their homespun lightdm greeters
The set of utilities specified in POSIX is, erm, not entirely sensible[1]. Though POSIX is more helpful than most large standards I’ve seen, it still ends up mostly having partial implementations (are there any completely 2008-compliant systems, I wonder?).
Linux distros don’t follow a standard anymore, as as I can tell. And Linux was never entirely POSIX compliant.