diff --git a/man4/initrd.4 b/man4/initrd.4
index 512e2bd18..d4264b297 100644
--- a/man4/initrd.4
+++ b/man4/initrd.4
@@ -235,6 +235,19 @@ IP number 193.8.232.7 and named 'idefix':
 	  >/proc/sys/kernel/nfs-root-addrs
 	echo 255 >/proc/sys/kernel/real-root-dev
 .fi
+
+.BR Note :
+The use of
+.BR /proc/sys/kernel/real-root-dev
+to change the root file system is obsolete.
+See the kernel source file
+.I Documentation/initrd.txt
+as well as
+.BR pivot_root (2)
+and
+.BR pivot_root (8)
+for information on the modern method of changing the root file system. 
+.\" FIXME the manual page should describe the pivot_root mechanism.
 .\"   
 .\"   
 .\"