I do not see any documentation for the boot parameter iso-scan/filename=. I see the parameter is handled by the script at location scripts/casper-premount/20iso_scan in Ubuntu's initrd. Here is the script.

What is the closest thing to documentation that exists for this boot parameter?

Also is there any comprehensive list of the boot parameters which are available in Ubuntu?

  • rocky's answer is a good answer. I would like to see does anybody else have thoughts or knowledge on the matter.
    – brendan
    Jul 4 '15 at 14:37
  • Well, in the grub2 install script, one may see things like linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=/boot-repair-disk-64bit.iso splash --. This means that the "linux file" cmd of grub2 is run (see manual), and the description of that is: "Load a Linux kernel image from file. The rest of the line is passed verbatim as the kernel command-line." ... so anything beyond the filename is meant for kernel argument processing, which can only be doc'd on the level of a particular linux distribution, family or version. Aug 8 '16 at 18:02

The french wikipedia article on casper says this (translated into English)

The main phases starting...

If requested by iso-scan / filename = / xxx, looking for an .iso image of CD whose name is / xxx

And the shell script code verifies that this is how it works.

As for a comprehensive list of boot parameters, there isn't likely to be one for such a broad question. That's like asking if there is a comprehensive list of documentation for shell scripts. Those parameters go to the thing that gets control of boot, and as far as I know anyone can write such a thing.

  • As a new user, if this answers the question, check the check mark and/or hit the ^ arrow. That will increase your reputation.
    – rocky
    Jul 4 '15 at 14:57
  • I pressed the up arrow but it said I can't change the public score. I'd like to see if there are other answers before I accept your answer if it's ok :) Thank you
    – brendan
    Jul 4 '15 at 15:24

The correct source for that script is from lupin-casper package in Ubuntu

Description: Add support for loop-mount installations to casper The Wubi installer provides a means for installing Ubuntu into a loop-mounted filesystem image hosted on a Windows filesystem. lupin-casper provides hooks to find an ISO image on a hard disk and to read a preseed file from a hard disk, which are used in the early part of this process.

An initramfs hook installs /scripts/casper-premount/20iso_scan inside the initramfs / initrd. If you make a custom live-build Ubuntu based ISO, you need to include that package to have Grub2 be able to live boot.

find_iso parameter was renamed to iso-scan/filename= which sets LIVEMEDIA which is queried in find_livefs in /scripts/casper

Without iso_scan script, you end up stuck in initramfs console with error message: unable to find a medium containing a live file system

Example grub configuration:

menuentry "Ubuntu Live CD" {
    set isofile="/efi/boot/ubuntu.iso"
    loopback loop (hd0,msdos1)$isofile
    linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile noprompt noeject debug
    initrd (loop)/casper/initrd.lz

Hope that helps someone... finding the source of iso_scan was rather difficult.

  • I don't see the error message without "iso_scan". Instead, I found that I can just copy all the files of the ubuntu live dvd to a hard drive partition and boot from there (no setting loopback and replacing (loop) with (hd0,msdos1)).
    – shaoyl85
    Mar 12 '18 at 5:38

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