Bootable USB disk that lets you choose an ISO image

This is basically a newer iteration on https://mg.pov.lt/blog/booting-iso-from-usb.html

Creating a bootable USB disk that lets you boot any Ubuntu ISO image:

1. Mount a USB disk with a sufficient amount of free space. Note the device name (e.g. /dev/sdb) and the mount point (e.g. /media/mg/MG-FLASH).

2. Install GRUB:

   sudo grub-install --target=i386-pc \
                     --root-directory=/media/mg/MG-FLASH /dev/sdb
   

   (you may have to also use --force)

3. Perhaps also install an UEFI bootloader

   sudo grub-install --target=x86_64-efi --removable \
                     --root-directory=/media/mg/MG-FLASH \
                     --efi-directory=/media/mg/MG-FLASH /dev/sdb
   

   (be very careful not to forget --removable, or it'll overwrite your EFI boot variables and your host machine will fail to boot!)

4. Download Ubuntu ISO images you want

   cd /media/mg/MG-FLASH
   git clone https://github.com/mgedmin/ubuntu-images ubuntu
   cd ubuntu
   # maybe edit the Makefile to pick what Ubuntu versions and variants you want
   make verify-all
   

5. Check out this repository (this is tricky because git doesn't want to check out things into an existing non-empty directory)

   git clone https://github.com/mgedmin/bootable-iso /tmp/bootable-iso
   mv /tmp/bootable-iso/.git /media/mg/MG-FLASH/boot/grub/
   mv /tmp/bootable-iso/* /media/mg/MG-FLASH/boot/grub/
   

6. Run make -C /media/mg/MG-FLASH/boot/grub/ to build a grub.cfg that matches your Ubuntu images

7. Test that things work

Testing with KVM

1. Find the device name

   udisksctl status
   

2. Run

   sh kvmboot /dev/sdb1
   

3. Record the test results in mkgrubcfg.py

Other resources

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

• You may be interested in Ventoy, which seems a much more polished and capable solution for this kind of thing.