isatty.3: Most non-tty files nowadays result in the error ENOTTY

Historically, at least FIFOs and pipes yielded the error EINVAL.

Reported-by: Jakub Wilk <jwilk@jwilk.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man3/isatty.3 b/man3/isatty.3
index 60639c617b50673510dbd7e6470d3d013f1b3595..ffb0ff24cb676d4eb9bf56a6727069a6064b35ac 100644 (file)
--- a/man3/isatty.3
+++ b/man3/isatty.3
@@ -52,13 +52,15 @@ is set to indicate the error.
 .I fd
 is not a valid file descriptor.
 .TP
-.B EINVAL
+.B ENOTTY
 .I fd
 refers to a file other than a terminal.
-POSIX.1 specifies the error
-.BR ENOTTY
-.\" FIXME . File a bug for this?
-for this case.
+On some older kernels, some types of files
+.\" e.g., FIFOs and pipes on 2.6.32)
+resulted in the error
+.B EINVAL
+in this case (which is a violation of POSIX, which specifies the error
+.BR ENOTTY ).
 .SH ATTRIBUTES
 For an explanation of the terms used in this section, see
 .BR attributes (7).