Example /boot/grub/custom.cfg For Multiple ISOs

menuentry "Kali OS ISO" {
    set root=(hd0,4)
    set iso="/ISO/kali-linux-xfce-2019.2-amd64.iso"
    set bootoptions="findiso=$iso boot=live noconfig=sudo username=root hostname=kali quiet splash"
    search --set -f $iso
    loopback loop (hd0,4)$iso
    linux (loop)/live/vmlinuz $bootoptions
    initrd (loop)/live/initrd.img
}

menuentry "Manjaro Gnome ISO" {
    set isofile="/ISO/manjaro-gnome-18.0.4-stable-x86_64.iso"
    set dri="free"
    search --no-floppy -f --set=root $isofile
    probe -u $root --set=abc
    set pqr="/dev/disk/by-uuid/$abc"
    loopback loop $isofile
    linux  (loop)/boot/vmlinuz-x86_64  img_dev=$pqr img_loop=$isofile driver=$dri tz=utc lang=en_us keytable=us
    initrd  (loop)/boot/intel_ucode.img (loop)/boot/initramfs-x86_64.img
}

menuentry "Manjaro KDE ISO" {
    set isofile="/ISO/manjaro-KDE-18.1.0-stable-x86_64.iso"
    set dri="free"
    search --no-floppy -f --set=root $isofile
    probe -u $root --set=abc
    set pqr="/dev/disk/by-uuid/$abc"
    loopback loop $isofile
    linux  (loop)/boot/vmlinuz-x86_64  img_dev=$pqr img_loop=$isofile driver=$dri tz=utc lang=en_us keytable=us
    initrd  (loop)/boot/intel_ucode.img (loop)/boot/initramfs-x86_64.img
}