here is the present source code for glibc where faccessat2 is used. What you say is true for some cases; if glibc is built for kernel versions below 0x050800 th

here is the present source code for glibc where faccessat2 is used. What you say is true for some cases; if glibc is built for kernel versions below 0x050800 then it doesn't assume faccessat2, here it falls back to faccessat for some cases - and faccessat was added in 2.6.16. But if you have flags other than AT_SYMLINK_NOFOLLOW or AT_EACCESS the call just fails without doing the fallback. See https://github.com/bminor/glibc/blob/595c22ecd8e87a27fd19270ed30fdbae9ad25426/sysdeps/unix/sysv/linux/faccessat.c#L36 https://github.com/bminor/glibc/blob/595c22ecd8e87a27fd19270... TIL that this this glibc mirror is kept in sync with the real one https://github.com/bminor/glibc https://github.com/bminor/glibc