Add pivot_root(8)

Makefile

@@ -17,6 +17,7 @@ SRC = \
 	lsmod.c             \
 	mkswap.c            \
 	mount.c             \
+	pivot_root.c        \
 	reboot.c            \
 	rmmod.c             \
 	stat.c              \

pivot_root.c

@@ -0,0 +1,28 @@
+/* See LICENSE file for copyright and license details. */
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <stdio.h>
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: %s new-root put-old\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND;
+
+	if (argc < 2)
+		usage();
+
+	if (syscall(SYS_pivot_root, argv[0], argv[1]) < 0)
+		eprintf("pivot_root:");
+
+	return 0;
+}