I have an ISO of customized GCompris based on Ubuntu. It is intended to be burned on a CD (iso 9660 FS Type). When I try to burn it to a USB, the pendrive "becomes" a CD and it won't boot...

The guy who made this ISO as a school project a while back, says he can't remember how he made it in the first place, but it has something to do with extracting the squashfs and re-create it using chroot.

Can any of you point me to a step by step guide on how to do it - from the top?

  • Have you tried dding it? That works for regular Ubuntu ISOs. Commented Jun 25, 2016 at 11:24
  • @AndroidDev it depends on the type filesystem embedded in the .iso.
    – Matthieu
    Commented Nov 7, 2018 at 11:48

2 Answers 2


Here is an answer using the same utilities from ipse lute's answer, but with a full procedure and more detail, as requested by the OP.

CAUTION: this procedure uses the dd command; please ensure that you know how to use it properly.


This document explains how to "hybridize" an ISO 9660 filesystem (.iso file), such that it can be booted from optical media and disk storage devices such as USB flash drives. This process is achieved using tools developed by the Syslinux Project: http://www.syslinux.org/wiki/index.php?title=The_Syslinux_Project



Initial setup: Install the required software

sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) main universe"

sudo apt-get install syslinux isolinux syslinux-utils syslinux-efi
  1. Determine if your ISO is non-hybridized, run:

    fdisk -l <your.iso>

    You will see output like (exact contents may differ):

    Disk your.iso: 709.3 MiB, 743718912 bytes, 1452576 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

    If you already have a hybridized ISO, you will see output like the following (Ubuntu Trusty Desktop used as an example; all Ubuntu ISOs are hybridized; formatting from stdout has been mangled here):

    Disk ubuntu-14.04.4-desktop-amd64.iso: 1020 MiB, 1069547520 bytes, 2088960 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: 0x1a447608
    Device                            Boot Start     End Sectors  Size Id Type
    ubuntu-14.04.4-desktop-amd64.iso1 *        0 2088959 2088960 1020M  0 Empty
    ubuntu-14.04.4-desktop-amd64.iso2      26268   30811    4544  2.2M ef EFI (FAT-12/16/32)
  2. If your ISO is already hybridized, skip to step 4. If you have a non-hybridized ISO, install the appropriate packages as follows: In a Debian Linux distro, run as root (e.g with sudo):

    apt-get install syslinux isolinux syslinux-utils syslinux-efi
  3. Hybridization: If you would like to retain your original, un-hybridized ISO, first make a new copy, which we will call your.hybrid.iso. On the new copy, Run:

    isohybrid <your.hybrid.iso>

    Note: this will overwrite the contents of the existing ISO. If you don't need the original, simply operate on it.

  4. Make a bootable disk from the ISO (e.g. USB flash drive)

    1. Determine the device file assigned to the USB drive. Open a terminal and run

      tail -f /var/log/syslog

      This will allow you to be ABSOLUTELY SURE which device file the kernel assigns to the device when it is inserted. You should see a line like:

      Aug  5 11:04:34 yourbox kernel: [2407408.163088] sd 23:0:0:0: [sdX] Attached SCSI removable disk

      This indicates that the USB drive was assigned /dev/sdX, where X is usually a lowercase alphabetic character.

      1. Insert the USB drive, and note the device file /dev/sdX by watching the output of syslog.
    2. Unmount all partitions of the flash drive, if any were automatically mounted.

    3. Dump the file to the USB drive. Use WITH EXTREME CAUTION dd to dump the ISO to the drive

      1. Make absolutely sure you replace X with the letter associated with your drive's device file in the following command, and that you make NO typos (e.g. stray whitespace) in the arguments!! If you mess up, you could destroy your whole system.

      2. Run, as root:

        dd if=<your.hybridized.iso> of=/dev/sdX bs=4M && sync
  5. Remove the USB drive, insert it into the machine to be booted, and boot from the USB drive in BIOS mode. By default, isohybrid will create a BIOS mode bootable drive, but there is an option to create a UEFI bootable drive. See man isohybrid for more information.

  6. Enjoy installing your new OS!

  • 1
    Good explanation of isohybrid and hybrid iso files. The cloning procedure will be safer if you use Disks (alias gnome-disks) or mkusb. These tools clone (using dd or an equivalent method under the hood), but provide a final checkpoint in a dialogue, which reduces the risk to overwrite valuable data. See these links, help.ubuntu.com/community/Installation/FromUSBStick, help.ubuntu.com/community/mkusb
    – sudodus
    Commented Jun 30, 2017 at 8:52
  • 1
    I wish @PenguinCSC would accept this answer.
    – Matthieu
    Commented Nov 7, 2018 at 11:48
  • 1
    In trying to follow this answer, I ran into the error "isohybrid: hybridized-ubuntu-10.04-desktop-amd64.iso: boot loader does not have an isolinux.bin hybrid signature. Note that isolinux-debug.bin does not support hybrid booting" and the .iso file was unmodified. I gave up and used an actual CD-ROM drive, which worked.
    – Julian
    Commented Mar 2, 2022 at 0:03
  • It's like isohybrid just toggles a flag for the iso. It doesn't work if the original iso doesn't support hybrid booting.
    – Humpity
    Commented Nov 9, 2023 at 19:52

Install a program called 'syslinux' by sudo apt-get install syslinux. Then create/obtain an ISO9660 file (e.g. filename.iso). In a terminal window type: isohybrid filename.iso. Now the iso file is hybrid, you can use it as CD and USB image file. The hybridization process will change the checksum of the file. Make sure to check it against the new checksum.

You can find more details here: http://www.syslinux.org/wiki/index.php?title=Isohybrid.

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