@node fchmodat
@subsection @code{fchmodat}
@findex fchmodat

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/fchmodat.html}

Gnulib module: fchmodat
@mindex fchmodat

Portability problems fixed by Gnulib:
@itemize
@item
This function is missing on some platforms:
glibc 2.3.6, Mac OS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 3.8, Minix 3.1.8,
AIX 5.1, HP-UX 11, Solaris 10, Cygwin 1.5.x, mingw, MSVC 14.
But the replacement function is not safe to be used in libraries and is not multithread-safe.
@item
This function does not fail when the file name argument ends in a slash
and (without the slash) names a non-directory, on some platforms:
AIX 7.2.
@item
When given the @code{AT_SYMLINK_NOFOLLOW} flag,
this function fails with @code{errno} set to @code{ENOTSUP},
even when the file is not a symbolic link:
GNU/Linux with glibc 2.31, Cygwin 2.9.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
Some platforms do not allow changing the access bits on symbolic
links.

@item
If the @code{AT_SYMLINK_NOFOLLOW} flag is specified,
this function can fail with @code{errno} set to @code{EMFILE} or @code{ENFILE},
and it fails with @code{errno} set to @code{EOPNOTSUPP} if the
@file{/proc} file system is not mounted:
GNU/Linux with glibc 2.34.

@item
This function sometimes fails with @code{EACCES} when the failure is
due to lack of appropriate privileges (@code{EPERM}), not to
search permission denied on the file name prefix (@code{EACCES}):
Linux kernel 5.15 with glibc 2.35 and a CIFS v1 file system
(see @url{https://bugs.gnu.org/65599}).
@end itemize
