--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/usr/ln.c	Fri May 26 23:11:05 2017 +0900
@@ -0,0 +1,15 @@
+#include "types.h"
+#include "stat.h"
+#include "user.h"
+
+int
+main(int argc, char *argv[])
+{
+    if(argc != 3){
+        printf(2, "Usage: ln old new\n");
+        exit();
+    }
+    if(link(argv[1], argv[2]) < 0)
+        printf(2, "link %s %s: failed\n", argv[1], argv[2]);
+    exit();
+}