Re: [gentoo-user] Re: [OT] Making a bootable USB flash drive from ISO image

[Neil Bothwick]

On Fri, 3 Oct 2014 15:19:40 +0000 (UTC), James wrote:

> > I was also wrong in stating I use isohybrid for the LXFDVDs. I used to
> > but since switching to using GRUB to boot the DVDs, there is no need
> > for it. GRUB bootable DVD ISOs can boot from USB sticks by default.

> Can you elaborate? For example how do you know a given *.iso* is grub
> bootable? It there a test?  Is there a list? Just burn it to a usbstick
> and test?

I'm not referring to booting ISOs from GRUB here, the LXFDVDs use GRUB as
their bootloader, instead of isolinux, which allows for various options
for the builder (me) that aren't available with isolinux.

As fr as booting individual ISOs with GRUB, you can boot any ISO this
way, the problem is telling the distro's init script that you have done
so and that is should look for an ISO image instead of a DVD drive to
load the rest of the files.

With some distros this is trivial, anything Ubuntu derived simply seeds
an extra kernel option to specify the location of the ISO. For others I
had to modify the initrd to get it to work while some have so far
defeated me.

Most do work, but you need to Google for the specifics for that
particular distro, there is no standard way. One Arch-derivative even
changed the names of all the variables in the init script for no apparent
reason other than to pretend it wasn't an arch script.

> Justuse a tool such as the aforementioned "isohybrid" can
> convert any *.iso* to a grub bootable?  I like the idea of one image
> (iso) being able to install via MBR or grub.

I usually put a System Rescue Cd image in /boot and have this as an
executable file in /etc/grub.d

#!/bin/sh

BOOT_PART="hd0,gpt1"

ISOS=$(ls -1r /boot/systemrescuecd-x86-*.iso)
if [[ -n "$ISOS" ]]; then
	echo -e "submenu \"System Rescue CD\" {"
	echo -e "\tset root='$BOOT_PART'"
	for i in $ISOS; do
		ISO=$(basename $i)
		VER=$(echo $ISO | sed 's/systemrescuecd-x86-\(.*\)\.iso/\1/')
		echo -e "\n\tmenuentry \"System Rescue CD $VER - Std kernel\" {"
		echo -e "\t\tloopback loop /$ISO"
		echo -e "\t\tlinux (loop)/isolinux/rescue64 rootpass=yeahright setkmap=uk isoloop=$ISO"
		echo -e "\t\tinitrd
		(loop)/isolinux/initram.igz" echo -e "\t}"

		echo -e "\n\tmenuentry \"System Rescue CD $VER - Alt kernel\" {"
		echo -e "\t\tloopback loop /$ISO"
		echo -e "\t\tlinux (loop)/isolinux/altker64 rootpass=nochance setkmap=uk isoloop=$ISO"
		echo -e "\t\tinitrd (loop)/isolinux/initram.igz"
		echo -e "\t}"
		done
	echo -e "}\n"
	echo -e "menuentry ' ' { true }\n"
	fi


-- 
Neil Bothwick

Standard: (n., adj.) a design target which manufacturers may embellish, improve
          upon, or ignore as they wish, so long as it can be used profitably
          in their advertising.