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Re: Grub Troubleshooting

From: hoan
Subject: Re: Grub Troubleshooting
Date: Sat, 7 May 2016 10:41:42 +0000
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moreover,if I understand your initial intention to boot live debian from isoimage sitting on usb_stick ,then your menu_grub.cfg is far from your desire .Once grub hands over to kernel ,the kernel is missing lots of things,in particular rootfs stuffs....
I suggest you do as
menuentry "
debian-8.0.0-amd64-DVD-1.iso" {
       set isoloop=/iso/
       search -f -s $isoloop
       loopback loop $isoloop
       linux (loop)/live/vmlinuz findiso=$isoloop rootfstype=iso9660 boot=live components
       initrd (loop)/live/initrd.img
the kernel options allows to find where is sitting your isoimage,the partiton's filesystem,and use "live" as script_init
components is proper_debian_init_protocol to know what to setup at this stage.(I expect your liveiso is behind /iso/
directory of usbstick.)
To play safe,create /boot/grub/grub.cfg to this usbstick.where grub.cfg contains the previous menuentry.

boot with any grub you have,then in grub_console type
configfile (hd_usbstick)/boot/grub/grub.cfg

On 05/06/2016 10:56 AM, wangji wrote:
John Lewis <address@hidden> writes:

Is there a more efficient way to troubleshoot GRUB issues. Right now I
am in a nearly blind, change grub.cfg and boot. If there is an issue
with the initramfs  I am completely blind to how to fix that. Here is a
thread of me trying to resolve a a problem with booting a Debian DVD
with GRUB
from this debianforum link,you wrote:
set imgdevpath="/dev/disk/by-label/multiboot"

Code: Select all
   menuentry 'Debian Jessie amd64' {
           set isofile='/iso/debian-8.0.0-amd64-DVD-1.iso'
           loopback loop $isofile
           linux (loop)/install.amd/vmlinuz
           initrd (loop)/install.amd/initrd.gz
grub environment is totally independent of linux's
env-kernel_initramfs_world- all you can do is to hand over 
some parameters['s locations].
On real machine once grub gets into your grub's menu it needs to have the
right $root (eventually $prefix).

The imgdevpath is in nix's world,so your emulator can get grasp of it,but
not grub !!!!

On bare metal your grub's menu needs surely something of the kinds  
"search -f -s $isofile"          before the loopback line. 

As demo of multiboot of linuxaio-fedora23-amd64.iso which only boots in
legacy CSM mode.A correct grub.cfg is enough to make it boot on uefi_pc
using any current grub2-efi stick .
see: Put a
tiger grub on it/

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