CentOS grub2 booting iso via loopback

Question

I've got a usb-key setup to multi-boot different Linux images. I'm trying to add CentOS, here's a post with similar entries for grub.cfg

set drive_label=multipass01
set isopath=/iso

menuentry "CentOS-6.3-x86_64-LiveCD" {

# Tried the following root designations;
# root=live:LABEL="multipass01" 
# root=live:LABEL=multipass01 
# root=live:LABEL="multipass01":$isofile
# root=live:LABEL=multipass01:$isofile
# root=live:/dev/disk/by-label/$drive_label$isofile
# root=live:UUID=3A55-12BC:$isofile
# root=live:UUID=:$isofile
# root=UUID=3A55-12BC
# root=live:$isofile
# iso-scan/filename=$isofile

    set isofile="$isopath/CentOS-6.3-x86_64-LiveCD.iso"
    loopback loop $isofile
    linux (loop)/isolinux/vmlinuz0 boot=isolinux root=live:LABEL=multipass01:$isofile rootfstype=auto ro liveimg 3 rhgb rd.luks=0 rd.md=0 rd.dm=0 splash --
    initrd (loop)/isolinux/initrd0.img
}

Heres the result of attempting to boot this entry (regardless of which root=);

edit; related fedora bug

Answer 1

I tried the same approach as you(but the liveos is Fedora 17 for me), I failed too, we can't use isofile for root=live: option. root=live:LABEL=multipass01:$isofile can't be recognized(maybe it can be recognized in future fix, but I can't wait).

So I used a different approach:

#step 1 create a blank partition that can hold the liveos.(/dev/sdb5)

#step 2 copy the liveos to the partition
dd if=/my-path-to-f17-live-iso of=/dev/sdb5

#step 3 change the grub.cfg,
#note1: don't need to use loopback, just use (hdX,Y).
#note2: "root=" becomes "root=live:/dev/sdb5"
menuentry 'F17 install' --class fedora --class gnu-linux --class gnu --class os {
    insmod part_msdos
    linux (hd1,5)/isolinux/vmlinuz0 linux root=live:/dev/sdb5 rootfstype=auto ro liveimg rd.luks=0 rd.md=0 rd.dm=0 
    initrd (hd1,5)/isolinux/initrd0.img
}

You can try this approach too, the /dev/sdb5 act as a CD/DVD-rom in this approach.

Another approach is changing the python script of the dracut to make it recognize such options, but I don't think it is worth.