Syslinux

Syslinux provides the terminal way of setting up a Multiboot usb.

Multiboot USB

      # Format USB to Fat32 using Gparted or fdisk
      $ sudo apt install Syslinux
      # find where your usb is mounted
      $ lsblk
      $ sudo syslinux -s -i /dev/sda1
      $ sudo dd conv=notrunc bs=440 count=1 if=mbr.bin of=/dev/sda 
      $ sudo parted /dev/sda set 1 boot on
      # Find the mount point
      # lsblk
      $ cd /media/$USER/
      $ ls
      # you should see the usb mounted cd to it
      $ mkdir -p boot/syslinux
      $ cp /usr/lib/syslinux/bios/*.c32 boot/syslinux/

References

    https://wiki.syslinux.org/wiki/index.php?title=HowTos#How_to_Create_a_Bootable_USB:_For_Linux