Grub2: Please explain me what does this command do?

I'm learning grub2. The following code shows a menu entry to boot an ubuntu image.

> menuentry "Ubuntu 12.04.2 ISO" {
> set isofile="/home/<username>/Downloads/ubuntu-12.04.2-desktop-amd64.iso"
> # or set isofile="/<username>/Downloads/ubuntu-12.04.2-desktop-i386.iso"
> # if you use a single partition for your $HOME
> loopback loop (hd0,5)$isofile
> linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile noprompt noeject
> initrd (loop)/casper/initrd.lz }

Can somebody explain me what does the "boot=casper" and "iso-scan/filename=$isofile" in the above code do ?

1 Answer

1.boot=casper

From its man-page

Casper is a hook for initramfs-tools used to generate an initramfs capable to boot live systems as those created by make-live. This includes the Debian-Live isos, netboot tarballs, and usb stick images and Ubuntu live cds. At boot time it will look for a (read-only) media containing a "/casper" directory where a root filesystems (often a compressed squashfs) is stored. If found, it will create a writable environment, using unionfs, for debian like systems to boot from.

2 . For the second A very good information like with examples from ubuntu grub community and menuentry details.