problem when using livecd-iso-to-pxeboot

[Jiang Jim]

I want to pxe a official CentOS-6.3-x86_64-LiveCD.iso to other servers.
I face to some problem, I use livecd-iso-to-pxeboot to build a tftpboot/.

I can get vmlinuxz0 and initrd0.img

This is my pxelinux.cfg/default

DEFAULT pxeboot
TIMEOUT 20
PROMPT 0
LABEL pxeboot
        KERNEL livecd/vmlinuz0
        APPEND rootflags=loop initrd=livecd/initrd0.img
root=live:/CentOS-6.3-x86_64-LiveCD.iso rootfstype=auto ro liveimg
nodiskmount nolvmmount  rhgb vga=791 rd.luks=0 rd.md=0 rd.dm=0
rd.live.check
ONERROR LOCALBOOT 0


But someting wrong in root section

cannot open root device "live:/CentOS-6.3-x86_64-LiveCD.iso"


I want to find out where CentOS-6.3-x86_64-LiveCD.iso It put into initrd0.img

I extract the content of initrd0.img, but when I extract coip img,
700mb content become 21m

I can't find where the   CentOS-6.3-x86_64-LiveCD.iso is.

Then I found the code of livecd-iso-to-pxeboot

( cd "$ISODIRNAME" && echo "$ISOBASENAME" | cpio -H newc -L -o
) |
  gzip -9 |
  cat $CDMNT/isolinux/initrd0.img - > tftpboot/initrd0.img

I can't understand why this commend is using cat to put two file,
initrd and iso together.