Booting daily-live/current cosmic-desktop-amd64.iso from Grub2 and updating it using zsync.

Today I downloaded Ubuntu 1810 Cosmic Cuttlefish Live ISO

    wget -c http://cdimage.ubuntu.com/daily-live/current/cosmic-desktop-amd64.iso


 and used it booting from Grub2 menu entry as follows:

    sudo gedit /etc/grub.d/40_custom

and added the following lines:

    menuentry "Cosmic Desktop iso" {
            set isofile="/home/user/cosmic-desktop-amd64.iso"
            loopback loop (hd0,X)$isofile
            linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile noprompt noeject
            initrd (loop)/casper/initrd
    }

then I updated grub to add the menuentry:

    sudo update-grub

I could boot from the ISO selecting Cosmic Desktop iso from menu.

Today I decided to keep the ISO updated and installed zsync and used it to update.

    sudo apt-get install zsync -y
    zsync http://cdimage.ubuntu.com/daily-live/current/cosmic-desktop-amd64.iso.zsync
    #################### 100.0% 108.2 kBps DONE  

    reading seed file wily-desktop-amd64.iso: **************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************Read wily-desktop-amd64.iso. Target 100.0% complete.   
    verifying download...checksum matches OK
    used 1257062400 local, fetched 0

Since it is less than 24 hours it says " fetched 0"

If you want to use the method please note that the ISO is on /home folder of the user. Put your username replacing user and X in (hd0,X) as your partition no X.