Can't re-create initrd

I'm working on a local change to the initrd used by PXE for Fedora 20. The standard version works great for me. As an experiment, I ran these commands. # ls -l initrd.img -rw-r--r--. 1 root root 34631660 Dec 12 2013 initrd.img # mkdir newrd; cd newrd # unxz <../initrd.img | cpio -i # find . | cpio -o -c | xz >../initrd2.img The resulting initrd2.img has exactly the same size as the original file but the contents are not in the same sequence. That is, "cpio -t" on the two files shows the same number of files but not in the same order. I've also tried creating the new file with this command. # unxz <../initrd.img | cpio -it | cpio -o -c | xz >../initrd2.img This results in a new file with the contents in the same order as the original. But when I put initrd2.img in place of initrd.img and try to PXE boot, the boot fails with the message, "Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)". There may be more details before that message but they roll off my screen too quickly. What am I doing wrong? -- Dave Close