Multiboot USB drive

Related articles

• GRUB
• Syslinux
• Archiso

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

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

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 --efi-directory /mnt --boot-directory=/mnt/boot --removable

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

This configuration is useful for creating an 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 (type EF02)
2. An EFI System partition (type EF00 with a FAT32 filesystem)
3. Your data partition (use a filesystem supported by GRUB)

The BIOS boot partition must be sized 1 MB, while the EFI System partition can be at least as small as 50 MB. The data partition can take up the rest of the space of your drive.

Next you must create a hybrid MBR partition table, as setting the boot flag on the protective MBR partition might not be enough.

Hybrid MBR partition table creation example using gdisk:

# gdisk /dev/sdX

Command (? for help): r
Recovery/transformation command (? for help): h
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 #2)
Enter an MBR hex code (default EF): 
Set the bootable flag? (Y/N): N

Creating entry for GPT partition #2 (MBR partition #3)
Enter an MBR hex code (default EF): 
Set the bootable flag? (Y/N): N

Creating entry for GPT partition #3 (MBR partition #4)
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

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. Then, you can install GRUB for EFI with:

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

And for BIOS with:

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

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

# grub-install --target=i386-pc --boot-directory=/DATA_MOUNTPOINT/boot --recheck /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/aguslr/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/iso/ 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)$isofile. 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 ($isopart)$isofile

Tip: For a list of kernel parameters, see https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.rst and https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt (still incomplete)

Arch Linux monthly release

Also see archiso.

menuentry '[loopback]archlinux-2017.04.01-x86_64.iso' {
	set isofile='/boot/iso/archlinux-2017.04.01-x86_64.iso'
	loopback loop $isofile
	linux (loop)/arch/boot/x86_64/vmlinuz archisodevice=/dev/loop0 img_dev=$imgdevpath img_loop=$isofile earlymodules=loop
	initrd (loop)/arch/boot/x86_64/archiso.img
}

Note: As of archiso v23 (monthly release 2015.10.01), the parameter archisodevice=/dev/loop0 is no longer necessary when boot using GRUB and loopback devices.

archboot

Also see archboot.

menuentry '[loopback]archlinux-2014.11-1-archboot' {
	set isofile='/boot/iso/archlinux-2014.11-1-archboot.iso'
	loopback loop $isofile
	linux (loop)/boot/vmlinuz_x86_64 iso_loop_dev=$imgdevpath iso_loop_path=$isofile
	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#Installation^{[broken link: invalid section]}.

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.

Caveat for 32-bit systems

When booting a 32-bit system from an image larger than 128MiB, it is necessary to increase the maximum memory usage of vmalloc. This is done by adding vmalloc=valueM to the kernel parameters, where value is larger than the size of the ISO image in MiB.[1]

For example when booting the 32-bit system from the Arch installation ISO, press the Tab key over the Boot Arch Linux (i686) entry and add vmalloc=768M at the end. Skipping this step will result in the following error during boot:

modprobe: ERROR: could not insert 'phram': Input/output error

See also

• GRUB:
  • https://help.ubuntu.com/community/Grub2/ISOBoot/Examples
  • https://help.ubuntu.com/community/Grub2/ISOBoot
• Syslinux:
  • Boot an ISO image