cpio is not working properly in repacking initrd.lz for live

If I unpack initrd.lz and then repack it without making any changes, then replace it with my new initrd.lz in Casper directory for live CD. It is structed. While packing of initrd I got a warning message as below:

cpio: ./usr/share/plymouth/themes/text.plymouth: Cannot stat: No such file or directory.

Finally my question is, what is the utility to pack and unpack the initrd.lz?

Thanks.

Answer

Extract the contents of the initrd:

  mkdir temp
  cd temp
  lzma -dc -S .lz /mnt/casper/initrd.lz | cpio -id

Modify and Repack them into a new initrd:

  find . | cpio --quiet --dereference -o -H newc | lzma -7 > ~/new-initrd.lz

and for the text.plymouth check if the file is present