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Booting ISO Images in Mageia7

Years ago, I used GRUB and memdisk to boot directly from ISO images I kept in /boot/. Things like SpinRite, F4UBD, PLPBT and so on. It was pretty straightforward on 32-bit Linux using GRUB.

Then GRUB2 came along and I found it frustrating. What made it even worse was that much of what I found on the Internet was specific to Ubuntu and the non-standard way in which Ubuntu implements things. As well, for the Ubuntu crowd, solutions were presented as recipes, so copy-paste ruled the day without any explanation as to why certain settings were chosen and what options were available. In other words, it was difficult to translate these "solutions" to anything but Ubuntu Linux.

For Mageia, it is helpful to know what the distro uses as the default directories. Mageia provides the following file:

# /etc/grub-customizer/grub.cfg
# Configuration file for grub-customizer
#(not to be confused with grub.cfg for grub2)

#Command name changes for

Mageia.MKCONFIG_CMD=grub2-mkconfig

INSTALL_CMD=grub2-install

MKFONT_CMD=grub2-mkfont

# These are the default configuration file locations used by grub2 in Mageia.

CFG_DIR=/etc/grub.d

OUTPUT_DIR=/boot/grub2

OUTPUT_FILE=/boot/grub2/grub.cfg

SETTINGS_FILE=/etc/default/grub


Also note that to avoid confusion with GRUB commands, all GRUB2 commands in Mageia are prefixed with grub2-*.

Where Is the GRUB2 Bootloader Installed?

Reboot your machine and enter the GRUB2 menu and press C which brings you to the GRUB2 command prompt. For now, the only one that you need is: ls.


To discover this, the following two commands are useful.

$ sudo grub2-probe -t device /boot/grub2

which in my case, returns /dev/sdc1.

To discover the UUID of the device, 

$sudo grub2-probe -t fs_uuid /boot/grub2

which returns for me,

40906922-182b-4c6f-8cac-3267d104ade8

While the configuration file for GRUB2 is kept in /boot/grub2/grub.cfg, it is not to be edited directly. Instead, configuration files found in /etc/grub.d are accessed to build the configuration file that is ultimately used. The filename prefixes in that directory have specific meaning to GRUB2 and by default, the file 40_custom is intended to be modified by the user. The file must be executable to be included in the final configuration.

Let's create a custom GRUB2 menu entry for F4UBCD. Falcon 4's Universal Boot CD is Grub4DOS-based and provides many system utilities as well as a running Windows MiniXP . The intent is to provide tools to repair computer systems. The ISO image contains a readme.txt file with a plethora of information The information about the ISO image is:

$ sudo isoinfo -d -i /boot/F4UBCD.iso 
CD-ROM is in ISO 9660 format
System id: Win32
Volume id: F4UBCD v4.61
Volume set id: 
Publisher id: 
Data preparer id: 
Application id: MKISOFS ISO 9660/HFS FILESYSTEM BUILDER & CDRECORD CD-R/DVD CREATOR (C) 1993 E.YOUNGDALE (C) 1997 J.PEARSON/J.SCHILLING
Copyright File id: 
Abstract File id: 
Bibliographic File id: 
Volume set size is: 1
Volume set sequence number is: 1
Logical block size is: 2048
Volume size is: 357231
El Torito VD version 1 found, boot catalog is in sector 64
NO Joliet present
NO Rock Ridge present
Eltorito validation header:
    Hid 1
    Arch 0 (x86)
    ID ''
    Key 55 AA
    Eltorito defaultboot header:
        Bootid 88 (bootable)
        Boot media 0 (No Emulation Boot)
        Load segment 0
        Sys type 0
        Nsect 4
        Bootoff 42 66

But what kind of ISO image is it? Standard or Hybrid? Using fdisk -l on the image, a hybrid ISO image will look like a hard drive with partitions, a standard ISP image will look like this:
# fdisk -l  /boot/F4UBCD.iso
Disk /boot/F4UBCD.iso: 697.7 MiB, 731609088 bytes, 1428924 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

We may not need all this information, but that's how to get it if we do.

One extra component we may need is memdisk. It's part of the Syslinux package and can boot floppy images, hard disk images and some ISO images. However, Mageia7's version of syslinux does not provide memdisk.


Here's what a custom script will look like to boot a grub4dos ISP image, F4UBCD.iso.

menuentry "F4UBCD" {

This is our first line that provides the name of the menu entry to GRUB2; it always ends with a left curly bracket. The entire menu entry will end with a right curly bracket.

insmod iso9660
insmod part_msdos
insmod chain

These three lines load modules necessary for GRUB2 to look inside the image. These modules provide iso9660 support which is needed to read optical discs that use this filesystem, provide support for MS-DOS (MBR) partitions and partitioning tables and provide support for MS-DOS (MBR) partitions and partitioning tables.

chainloader (hd2,0)+1
}

This line invokes the chainloader on the hard drive discovered above.

RESOURCES
https://help-grub.gnu.narkive.com/nLb4Hafg/grub-2-how-boot-iso-with-memdisk

https://askubuntu.com/questions/1254298/boot-ubuntu-iso-pure-from-ramdisk-memdisk

http://www.ultimatebootcd.com/forums/viewtopic.php?p=9108#p9108

http://www.panticz.de/MultiBootUSB


https://www.gnu.org/software/grub/grub-documentation.html


https://pccloud9.com/Files/F4UBCD-4.61.iso

https://help.ubuntu.com/community/Grub2/CustomMenus

https://help.ubuntu.com/community/Grub2/ISOBoot

https://help.ubuntu.com/community/Grub2/ISOBoot/Examples

2

https://wiki.gentoo.org/wiki/GRUB2/Chainloading


https://unix.stackexchange.com/questions/15015/how-to-boot-from-iso-with-grub2-burg-boot-loader



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