add a bugs section.

lib/libc/net/rcmd.3

@@ -1,4 +1,4 @@
-.\"	$NetBSD: rcmd.3,v 1.10 1997/05/28 04:01:06 mrg Exp $
+.\"	$NetBSD: rcmd.3,v 1.11 1997/06/05 16:40:16 mrg Exp $
 .\"
 .\" Copyright (c) 1983, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -239,3 +239,27 @@ The (newer)
 .Fn rcmd
 function appeared in
 .Nx 1.3 .
+.Sh BUGS
+As the
+.Nm
+function uses
+.Xr getpwent 3
+functions,
+passing in a previous value from one of this family of functions
+can result in unpredictable results.  Do not write code like the
+following:
+.Bd -literal -offset indent
+struct passwd *pw;
+
+pw = getpwuid(getuid());
+...
+if (rcmd(host, port, pw->pw_name, pw->pw_name, cmd, fd2p) < 0)
+	err(1, "rcmd");
+
+.Ed
+.Pp
+When a reentrant version of
+.Xr getpwent 3
+is available,
+.Nm
+should be changed to use this instead.