Comment by gilgamesh3

>OpenBSD has had it since forever.

OpenBSD introduced mimmutable in OpenBSD 7.3, which was released 10/4/2023 (for US people, it would be 4/10/2023), so it isn't "forever".

Meanwhile Linux and FreeBSD has "memfd_create" forever while OpenBSD doesn't have anonymous files and relies on "shm_open".