open.2: Say a bit more about what happens when 'mode' is wrongly omitted

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man2/open.2 b/man2/open.2
index f83326cbc3742a321cdffc913397b0bcd042f2ae..aedbe0460df12f47185cfad2880003f740c6675f 100644 (file)
--- a/man2/open.2
+++ b/man2/open.2
@@ -289,20 +289,28 @@ mount options described in
 .IP
 The
 .I mode
-argument specifies the file mode bits be applied when a new file is created.
-This argument must be supplied when
+argument specifies the file mode bits to be applied when a new file is created.
+If neither
 .B O_CREAT
-or
+nor
 .B O_TMPFILE
 is specified in
-.IR flags ;
-if neither
+.IR flags ,
+then
+.I mode
+is ignored (and can thus be specified as 0, or simply omitted).
+The
+.I mode
+argument
+.B must
+be supplied if
 .B O_CREAT
-nor
+or
 .B O_TMPFILE
-is specified, then
-.I mode
-is ignored.
+is specified in
+.IR flags ;
+if it is not supplied,
+some arbitrary bytes from the stack will be applied as the file mode.
 .IP
 The effective mode is modified by the process's
 .I umask