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Boot multiple iso from USB using SYSLINUX

Partitions and Formatting

Partitions and Formatting on usb device

Create partitions and filesystem. You can find your device using "lsblk" command. In my case it is sdb.

Create two primary partitions partitions with any program fdisk/gdisk/parted/gparted your prefer. First reasonably large one is "0b" fat32 partition for boot files and the second one is for iso files. The first partition should be active.

The partition table should be looked as below

            Disk /dev/sdb: 3.69 GiB, 3963617280 bytes, 7741440 sectors
            Units: sectors of 1 * 512 = 512 bytes
            Sector size (logical/physical): 512 bytes / 512 bytes
            I/O size (minimum/optimal): 512 bytes / 512 bytes
            Disklabel type: dos
            Disk identifier: 0xbc1ec006

            Device            Boot  Start     End Sectors  Size Id Type
            /dev/sdb1         *      2048  206847  204800  100M  b W95 FAT32
            /dev/sdb2              206848 7741439 7534592  3.6G 83 Linux

Format both partitions: first as vfat and the second one as ext2

            sudo mkfs.vfat /dev/sdb1
            sudo mkfs.ext2 /dev/sdb2

Install syslinux

            sudo dd bs=440 count=1 conv=notrunc if=/usr/share/syslinux/mbr.bin of=/dev/sdb
            sudo syslinux --directory syslinux --install /dev/sdb1

Partitions and Formatting on usb disk image file.

You can create an empty image file, say syslinuxdisk.img, with fallocate, dd, or qemu-img commands

            fallocate -l 4G syslinuxdisk.img
            dd if=/dev/zero of=syslinuxdisk.img bs=1M count=4M
            qemu-img create -f qcow2 syslinuxdisk.img 4G

I prefer to make image file which exactly fit to usb drive.

            dd if=/dev/sdb of=syslinuxdisk.img bs=1M status=progress oflag=sync

Finally, you can partition image file in similar way as real device with e.g. fdisk.

            Disk syslinuxdisk.img: 3.69 GiB, 3963617280 bytes, 7741440 sectors
            Units: sectors of 1 * 512 = 512 bytes
            Sector size (logical/physical): 512 bytes / 512 bytes
            I/O size (minimum/optimal): 512 bytes / 512 bytes
            Disklabel type: dos
            Disk identifier: 0xbc1ec006

            Device            Boot  Start     End Sectors  Size Id Type
            syslinuxdisk.img1 *      2048  206847  204800  100M  b W95 FAT32
            syslinuxdisk.img2      206848 7741439 7534592  3.6G 83 Linux

Further format partitions as vfat and ext2 and install syslinux on the first partition.

            sudo dd bs=440 count=1 conv=notrunc if=/usr/share/syslinux/mbr.bin of=syslinuxdisk.img
            sudo losetup /dev/loop2 syslinuxdisk.img -o 1048576 --sizelimit 104857088
            sudo mkfs.vfat /dev/loop2
            sudo mkdir /mnt/usb
            sudo mount /dev/loop2 /mnt/usb
            sudo syslinux --directory syslinux --install /dev/loop2
            sudo umount /mnt/usb
            sudo losetup -d /dev/loop2
            sudo losetup /dev/loop5 syslinuxdisk.img -o 105906176 --sizelimit 3962568192
            sudo mkfs.ext2 /dev/loop5
            sudo mount /dev/loop5 /mnt/usb

Copy iso files

Create a directory, e.g. ISO, on the second partition and copy iso files in the directory

            sudo mkdir /mnt/usb/ISO
            sudo rsync --info=progress2 openSUSE-Leap-15.3-KDE-Live-x86_64-Media.iso /mnt/usb/ISO/opensuse.iso
            sudo umount /mnt/usb

Syslinux configuration

I prefer to copy main syslinux files in the root directory on vfat partition, so that /dev/sdb1 partition has following structure:

            boot
            boot/syslinux/....
            boot/menu/
            boot/menu/default.cfg
            boot/menu/tools.cfg
            boot/menu/opensuse.cfg
            boot/grub
            ......
            suseboot
            suseboot/linux
            suseboot/initrd
            open
            cmd.c32
            hdt.c32
            ldlinux.c32
            ldlinux.sys
            libcom32.c32
            libgpl.c32
            liblua.c32
            libmenu.c32
            libutil.c32
            menu.c32
            suseboot
            syslinux.cfg

Main configurational file syslinux.cfg is found in the root directory whereas other cfg files are located in the directory /boot/menu

The default.cfg file contains the menu layout commands. I use a nice very simple layout:

            #default.cfg
            MENU TITLE Boot USB - Main menu
            MENU MARGIN 0
            MENU ROWS -9
            MENU TABMSG
            MENU TABMSGROW -3
            MENU CMDLINEROW -3
            MENU HELPMSGROW -4
            MENU HELPMSGENDROW -1
            MENU COLOR SCREEN 37;40
            MENU COLOR BORDER 34;40
            MENU COLOR TITLE 1;33;40
            MENU COLOR SCROLLBAR 34;46
            MENU COLOR SEL 30;47
            MENU COLOR UNSEL 36;40
            MENU COLOR CMDMARK 37;40
            MENU COLOR CMDLINE 37;40
            MENU COLOR TABMSG 37;40
            MENU COLOR DISABLED 37;40
            MENU COLOR HELP 32;40

The tools.cfg includes some useful tools:

            #tools.cfg
            MENU SEPARATOR
 
            LABEL -
                MENU LABEL BOOT TOOLS:
                MENU DISABLE
            
            LABEL hdt
                MENU LABEL Hardware Info
                COM32 hdt.c32
            
            LABEL reboot
                MENU LABEL Reboot
                COM32 /boot/syslinux/reboot.c32

The main config file, syslinux.cfg, enables boot different linux live OS as well as other loaders such as GRUB.

            UI /boot/syslinux/menu.c32
            MENU INCLUDE /boot/menu/defaults.cfg

            LABEL -
                MENU LABEL BOOT TYPES:
                MENU DISABLE
            
            LABEL Boot from Hard Drive
                MENU LABEL Windows 10 (hd0)
                KERNEL /boot/syslinux/chain.c32
                APPEND hd0
                MENU DEFAULT

            LABEL opensuse
                MENU LABEL openSUSE Live ISO 
                KERNEL /boot/syslinux/menu.c32
                APPEND /boot/menu/opensuse.cfg
            
            LABEL usbosboot
                MENU LABEL Boot OS from USB
                KERNEL /boot/syslinux/vesamenu.c32
                APPEND /boot/menu/usbosboot.cfg
            
            LABEL grub4dos
                MENU LABEL GRUB4DOS
                KERNEL /boot/grub/grub.exe
            
            LABEL grub2
                MENU LABEL GRUB2
                COM32 /boot/syslinux/chain.c32
                APPEND file=/boot/grub2/i386-pc/core.img

            MENU INCLUDE /boot/menu/tools.cfg

The only relevant part related to iso boot is under label opensuse where opensuse.cfg looks like

            #opensuse.cfg
            MENU INCLUDE /boot/menu/defaults.cfg

            LABEL -
                MENU LABEL BOOT OS:
                MENU DISABLE

            LABEL livesuse
                MENU LABEL openSUSE LiveDVD 15.3 Leap (nopersistent)
                LINUX /suseboot/linux
                APPEND root=UUID=c08caa7d-be72-4400-9930-0a46a5134bd7 rw rootwait  iso-scan/filename=/ISO/openSUSE.iso root=live:CDLABEL=openSUSE_Leap_15.3_KDE_Live loader=isolinux splash=silent quiet showopts initrd=/suseboot/initrd
            
            MENU SEPARATOR
            
            LABEL -
                MENU LABEL BOOT DEVELOPMENT (not working):
                MENU DISABLE

            LABEL suselin1
                MENU LABEL openSUSE LiveDVD 15.3 Leap - CDLABEL
                set isofile="/ISO/openSUSE.iso"
                set isolabel="openSUSE_Leap_15.3_KDE_Live"
                loopback loop $isofile
                LINUX (loop)/boot/x86_64/loader/linux boot=isolinux iso-scan/filename=$isofile root=live:CDLABEL=$isolabel ro rd.live.image rhgb
                APPEND initrd=(loop)/boot/x86_64/loader/initrd
            
            
            LABEL livesuse2
                MENU LABEL openSUSE LiveDVD 15.3 Leap 
                set isofile="/ISO/openSUSE.iso"
                set isolabel="openSUSE_Leap_15.3_KDE_Live"
                LINUX /suseboot/linux
                APPEND root=UUID=c08caa7d-be72-4400-9930-0a46a5134bd7 rw rootwait  iso-scan/filename=$isofile root=live:CDLABEL=$isolabel loader=isolinux splash=silent quiet showopts initrd=/suseboot/initrd
            
            LABEL suselin3
                MENU LABEL openSUSE LiveDVD 15.3 Leap - rd.live.image rhgb
                LINUX /suseboot/linux
                APPEND root=UUID=c08caa7d-be72-4400-9930-0a46a5134bd7 rw rootwait loop=/ISO/openSUSE.iso loader=isolinux rd.live.image rhgb initrd=/suseboot/initrd
                
            LABEL susemem2
                MENU LABEL openSUSE LiveDVD 15.3 Leap - memdisk try?
                KERNEL /boot/syslinux/memdisk
                APPEND root=UUID=c08caa7d-be72-4400-9930-0a46a5134bd7 rw rootwait initrd=/ISO/openSUSE.iso iso raw 
                
            LABEL susechain
                MENU LABEL openSUSE LiveDVD 15.3 Leap - chain
                KERNEL /boot/syslinux/chain.c32
                APPEND hd1 1 initrd=ISO/openSUSE.iso
                
            LABEL susechain2
                MENU LABEL openSUSE LiveDVD 15.3 Leap - chain disk1
                KERNEL /boot/syslinux/chain.c32
                APPEND hd1 1 boot isolinux=/opensuse/boot/x86_64/loader/isolinux.bin
                
            LABEL susechain3
                MENU LABEL openSUSE LiveDVD 15.3 Leap - chain disk0
                KERNEL /boot/syslinux/chain.c32
                APPEND hd0 1 boot isolinux=/opensuse/boot/x86_64/loader/isolinux.bin

            MENU INCLUDE /boot/menu/tools.cfg

All entries under BOOT DEVELOPMENT are non working and are given only for references.

UUID of the partition with iso files (/dev/sdb2) can be found with blkid command:

            sudo blkid /dev/sdb2
            #output:
            /dev/sdb2: UUID="c08caa7d-be72-4400-9930-0a46a5134bd7" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="bc1ec006-02"

Finally, one should put kernel and initrd files from linux distribution on FAT partition. I put the them on both partitions in the directory opensuse.

            sudo mount -o loop openSUSE-Leap-15.3-KDE-Live-x86_64-Media.iso /mnt/iso
            sudo mount /dev/sdb1 /mnt/usb
            sudo mkdir /mnt/usb/suseboot
            sudo cp /mnt/iso//boot/x86_64/loader/linux /mnt/usb/suseboot/
            sudo cp /mnt/iso//boot/x86_64/loader/initrd /mnt/usb/suseboot/
            sudo umount /mnt/usb
            sudo umount /mnt/iso

Now you can try to boot opensuse from usb.

For testing of the image or usb stick one can use qemu

            qemu-system-x86_64 -m 512 -hda syslinuxdisk.img (or /dev/sdb)

Good luck!

Boot Linux from USB. part I

Boot Linux from USB. part II

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