--- Net2/arch/i386/floppy/umount/umount.c	2018/04/24 18:04:01	1.1.1.1
+++ Net2/arch/i386/floppy/umount/umount.c	2018/04/24 18:05:27	1.1.1.2
@@ -42,6 +42,11 @@ main(argc, argv)
 	int argc;
 	char **argv;
 {
+	
+	if (argc == 1) {
+		err("usage: umount [dir ...]", 0);
+		_exit(1);
+	}
 	if (*++argv && **argv == '-') {
 		err("no options available", 0);
 		_exit(1);