Ubuntu/Debian Linux/Unix Howto Setup Install Syslinux Bootable USB with EFI and MBR from Command Line/CLI Terminal

There aren't too many simple guides that show you how to use commands to setup your USB or other drive as a normal bootable drive where you can easily boot custom kernels or whatever OS you would like.

1. Get the tools we need:

We install "syslinux" for MBR and "syslinux-efi" for EFI and "MBR" as we need a tool that embeds the actual MBR into our USB:

sudo apt install syslinux syslinux-efi mbr

2.) Format the Drive as VFAT/FAT:

This assumes your USB is partitioned and is partition 1 on drive sdj /dev/sdj1

mkfs.vat /dev/sdj1

#you may need to mark the partition as bootable in fdisk by hitting the "b" flag

3.) Install MBR onto the drive

Install the MBR on /dev/sdj

sudo install-mbr /dev/sdj

Now install syslinux to the partition

sudo syslinux -i /dev/sdj1

Download syslinux 6.04

https://mirrors.edge.kernel.org/pub/linux/utils/boot/syslinux/Testing/6.04/syslinux-6.04-pre1.zip

Extract it.

Install the EFI syslinux:

Mount it first:

mount /dev/sdj1 /mnt/sdj1

cd /mnt/sdj1

mkdir -p EFI/BOOT

#copy the EFI32 and EFI64 binaries to EFI/BOOT directory on your USB

BOOTIA32.efi BOOTX64.efi ldlinux.e32 ldlinux.e64

#file locations from .zip file linked above

./efi64/com32/elflink/ldlinux/ldlinux.e64

./efi64/efi/syslinux.efi #rename this to BOOTX64.efi

4.) Create your syslinux.cfg:

add this to syslinux.cfg in the root:
DEFAULT realtechtalk SAY Now booting the kernel from realtechtalk.com SYSLINUX... LABEL realtechtalk KERNEL kernelfs APPEND initrd=initrd.img

#you can add extra kernel flags after initrd=initrd.img by adding a specify a flag. eg initrd=initrd.img ro quiet nosplash