Multiboot USB drive

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A multiboot USB flash drive allows booting multiple ISO files from a single device. The ISO files can be copied to the device and booted directly without unpacking them first. There are multiple methods available, but they may not work for all ISO images.

Using GRUB and loopback devices

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Advantages:

  • only a single partition required
  • all ISO files are found in one directory
  • adding and removing ISO files is simple

Disadvantages:

  • not all ISO images are compatible
  • the original boot menu for the ISO file is not shown
  • it can be difficult to find a working boot entry

Preparation

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Reason: How much extra space is needed for the bootloader? (Discuss in Talk:Multiboot USB drive)

Create at least one partition and a filesystem supported by GRUB on the USB drive. See Partitioning and File systems#Create a file system. Choose the size based on the total size of the ISO files that you want to store on the drive, and plan for extra space for the bootloader.

Installing GRUB

Simple installation

Mount the filesystem located on the USB drive: 

# mount /dev/sdXY /mnt

Create the directory /boot: 

# mkdir /mnt/boot

Install GRUB on the USB drive: 

# grub-install --target=i386-pc --recheck --boot-directory=/mnt/boot /dev/sdX

In case you want to boot ISOs in UEFI mode, you have to install grub for the UEFI target: 

# grub-install --target=x86_64-efi --removable --boot-directory=/mnt/boot --efi-directory=/mnt

For UEFI, the partition has to be the first one in an MBR partition table and formatted with FAT32.

Hybrid UEFI GPT + BIOS GPT/MBR boot

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Reason: There is no reason to suggest the abominable hybrid MBR when other workarounds for BIOS/GPT booting exist. (Discuss in Talk:Multiboot USB drive)

This configuration is useful for creating a universal USB key, bootable everywhere. First of all you must create a GPT partition table on your device. You need at least 3 partitions:

  1. A BIOS boot partition (gdisk type code EF02). This partition must be 1 MiB in size
  2. An EFI system partition (gdisk type code EF00 with a FAT32 filesystem). This partition can be as small as 50 MiB.
  3. Your data partition (use a filesystem supported by GRUB). This partition can take up the rest of the space of your drive.

Next you must create a hybrid MBR partition table. Without it, a BIOS MBR based system will not boot. It will not find the partitions it expects to find.

Hybrid MBR partition table creation example using gdisk: 

# gdisk /dev/sdX
Command (? for help): r
Recovery/transformation command (? for help): h

WARNING! Hybrid MBRs are flaky and dangerous! If you decide not to use one,
just hit the Enter key at the below prompt and your MBR partition table will
be untouched.

Type from one to three GPT partition numbers, separated by spaces, to be added to the hybrid MBR, in sequence: 1 2 3
Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): N

Creating entry for GPT partition #1 (MBR partition #1)
Enter an MBR hex code (default EF):
Set the bootable flag? (Y/N): N

Creating entry for GPT partition #2 (MBR partition #2)
Enter an MBR hex code (default EF):
Set the bootable flag? (Y/N): N

Creating entry for GPT partition #3 (MBR partition #3)
Enter an MBR hex code (default 83):
Set the bootable flag? (Y/N): Y

Recovery/transformation command (? for help): x
Expert command (? for help): h
Expert command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): Y

Do not forget to format the partitions: 

# mkfs.fat -F32 /dev/sdX2
# mkfs.ext4 /dev/sdX3

You can now install GRUB to support both EFI + GPT and BIOS + GPT/MBR. The GRUB configuration (--boot-directory) can be kept in the same place.

First, you need to mount the EFI system partition and the data partition of your USB drive.

An example of this would be as follows: 

# mount /dev/sdX3 /mnt
# mkdir /mnt/boot /mnt/efi
# mount /dev/sdX2 /mnt/efi

Then, you can install GRUB for UEFI with:

In most cases EFI_MOUNTPOINT will correspond to the /mnt/efi directory on your mounted USB disk. DATA_MOUNTPOINT is where your data partition is mounted. In this example it would be the mount point of sdX3, /mnt. 

# grub-install --target=x86_64-efi --recheck --removable --efi-directory=/EFI_MOUNTPOINT --boot-directory=/DATA_MOUNTPOINT/boot

And for BIOS with: 

# grub-install --target=i386-pc --recheck --boot-directory=/DATA_MOUNTPOINT/boot /dev/sdX

As an additional fallback, you can also install GRUB on your MBR-bootable data partition: 

# grub-install --target=i386-pc --recheck --boot-directory=/DATA_MOUNTPOINT/boot /dev/sdX3

Configuring GRUB

Using a template

There are some git projects which provide some pre-existing GRUB configuration files, and a nice generic grub.cfg which can be used to load the other boot entries on demand, showing them only if the specified ISO files - or folders containing them - are present on the drive.

Multiboot USB: https://github.com/hackerncoder/multibootusb

GLIM (GRUB2 Live ISO Multiboot): https://github.com/thias/glim

Manual configuration

For the purpose of multiboot USB drive it is easier to edit grub.cfg by hand instead of generating it. Alternatively, make the following changes in /etc/grub.d/40_custom or /mnt/boot/grub/custom.cfg and generate /mnt/boot/grub/grub.cfg using grub-mkconfig.

As it is recommend to use a persistent name instead of /dev/sdxY to identify the partition on the USB drive where the image files are located, define a variable for convenience to hold the value. If the ISO images are on the same partition as GRUB, use the following to read the UUID at boot time: 

/mnt/boot/grub/grub.cfg
# path to the partition holding ISO images (using UUID)
probe -u $root --set=rootuuid
set imgdevpath="/dev/disk/by-uuid/$rootuuid"

Or specify the UUID explicitly: 

/mnt/boot/grub/grub.cfg
# path to the partition holding ISO images (using UUID)
set imgdevpath="/dev/disk/by-uuid/UUID_value"

Alternatively, use the device label instead of UUID: 

/mnt/boot/grub/grub.cfg
# path to the partition holding ISO images (using labels)
set imgdevpath="/dev/disk/by-label/label_value"

The necessary UUID or label can be found using lsblk -f. Do not use the same label as the Arch ISO for the USB device, otherwise the boot process will fail.

To complete the configuration, a boot entry for each ISO image has to be added below this header, see the next section for examples.

Boot entries

It is assumed that the ISO images are stored in the /boot-isos directory on the same filesystem where GRUB is installed. Otherwise it would be necessary to prefix the path to ISO file with device identification when using the loopback command, for example loopback loop (hd1,2)$iso_path. As this identification of devices is not persistent, it is not used in the examples in this section.

One can use persistent block device naming like so. Replace the UUID according to your ISO filesystem UUID. 

# define globally (i.e outside any menuentry)
insmod search_fs_uuid
search --no-floppy --set=isopart --fs-uuid 123-456
# later use inside each menuentry instead
loopback loop ($isopart)$iso_path
Tip: For a list of kernel parameters, see the kernel's command-line parameter documentation. For more examples of boot entries, see the GRUB upstream documentation or the documentation for the distribution you wish to boot.

Arch Linux monthly release

The ISO provides loopback.cfg. 

menuentry '[loopback]archlinux-2023.10.14-x86_64.iso' {
	set iso_path='/boot-isos/archlinux-2023.10.14-x86_64.iso'
	export iso_path
	search --set=root --file "$iso_path"
	loopback loop "$iso_path"
	root=(loop)
	configfile /boot/grub/loopback.cfg
	loopback --delete loop
}

Also see archiso.

MemTest86+

MemTest86+ is included in the monthly ISO. 

menuentry '[loopback]archlinux-2023.03.01-x86_64.iso MemTest86+' {
	set iso_path='/boot-isos/archlinux-2023.03.01-x86_64.iso'
	loopback loop $iso_path
	linux (loop)/boot/memtest86+/memtest.efi
}

Archboot

See Archboot Homepage. 

menuentry '[loopback]archlinux-2014.11-1-archboot' {
	set iso_path='/boot-isos/archlinux-2014.11-1-archboot.iso'
	loopback loop $iso_path
	linux (loop)/boot/vmlinuz_x86_64 iso_loop_dev=$imgdevpath iso_loop_path=$iso_path
	initrd (loop)/boot/initramfs_x86_64.img
}

Using Syslinux and memdisk

Using the memdisk module, the ISO image is loaded into memory, and its bootloader is loaded. Make sure that the system that will boot this USB drive has sufficient amount of memory for the image file and running operating system.

Preparation

Make sure that the USB drive is properly partitioned and that there is a partition with file system supported by Syslinux, for example fat32 or ext4. Then install Syslinux to this partition, see Syslinux#BIOS systems.

Install the memdisk module

The memdisk module was not installed during Syslinux installation, it has to be installed manually. Mount the partition where Syslinux is installed to /mnt/ and copy the memdisk module to the same directory where Syslinux is installed: 

# cp /usr/lib/syslinux/bios/memdisk /mnt/boot/syslinux/

Configuration

After copying the ISO files on the USB drive, edit the Syslinux configuration file and create menu entries for the ISO images. The basic entry looks like this: 

boot/syslinux/syslinux.cfg
LABEL some_label
    LINUX memdisk
    INITRD /path/to/image.iso
    APPEND iso

See memdisk on Syslinux wiki for more configuration options.

Automated tools

  • GRUB2 Live ISO Multiboot (GLIM) — A set of GRUB configuration files to turn a VFAT formatted USB memory stick with GNU/Linux distribution ISO images into a multiboot USB drive.
https://github.com/thias/glim || not packaged? search in AUR
  • liveusb-builder — A script suite to create multiboot USB stick for GNU/Linux distributions
https://github.com/mytbk/liveusb-builder || liveusb-builder-gitAUR
  • MultiBootUSB — A cross platform Python software with CLI and GUI interfaces which allows you to install and remove multiple live Linux images on a USB stick.
https://github.com/mbusb/multibootusb || multibootusbAUR
  • Ventoy — An open source tool to create bootable USB drive for ISO/WIM/IMG/VHD(x)/EFI files. You do not need to format the disk over and over, you just need to copy the files to the USB drive and boot them directly.
https://www.ventoy.net/ || ventoy-binAUR

See also