Rufus/Syslinux 6.04

Using Rufus, a window appears not described in documentation:

This image uses Syslinux 6.04 but this application only includes the installation files for Syslinux 6.04/pre1.

As new versions of Syslinux are not compatible with one another, and it wouldn’t be possible for Rufus to include them all, two additional files must be downloaded from the Internet (‘ldlinux.sys’ and ‘ldlinux.bss’):

  • Select ‘Yes’ to connect to the Internet and download these files
  • Select ‘No’ to cancel the operation

Note: The files will be downloaded in the current application directory and will be reused automatically if present.

Looking and getting help, issue has appeared since 2016~ using Rufus and depending on OS. Is it recommended to download the two files? ‘Yes’ must be clicked for the operation to continue for Qubes OS through Rufus. Any explanations or other solutions?

Thank you.

Make sure to select “dd” mode when using Rufus, the docs do have this line:

Be sure to select “DD image” mode ( after selecting the Qubes ISO)

I don’t think you will get that prompt if dd mode is used.

Where is that? Do not see it.

*“DD image” is to appear in window after "Start’, yet, the Syslinux 6.04 error appears. Maybe after “Yes”, “DD image” mode appears, yet, what to do about Syslinux 6.04 and two files downloaded from Internet? *And current Cluster size is “32 kilobytes (Default)”, yet in Documentation, it is “8192 kilobytes (Default)”.

Looks like the ability to select DD mode is missing from later versions of Rufus

Actually I just tested it. It does give you the option to select DD after you press start. (Rufus 3.12.1710)

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I see. Yet, what about two files from Internet for Qubes?

You can say yes to download the files if it does not allow you to go further, but those files are not used if you select DD mode.

When selecting DD mode, Rufus is doing a byte-for-byte copy of the qubes.iso file to the USB drive. Every byte starting from byte 0 of the USB drive will match your qubes.iso file. You want this, because hopefully you’ve already verified the PGP signature of the qubes.iso file, and this will ensure what is written to the disk matches what has been verified.

ISO mode does not copy byte-by-byte. It installs its own bootloader, reformats and partitions the USB drive, then copies files within the qubes.iso file to the USB drive. The files that it is asking to download are part of that process/bootloader. As the Qubes installer is signed over the whole qubes.iso file, there would be no way to verify the files that are written to the USB drive match what was in qubes.iso. On the positive side, it allows you to put other files on the USB drive, whereas DD mode makes the USB drive read-only, as it uses the ISO9660 read-only file system.


Don’t worry about downloading the files, because DD mode does not use them. But if you do not choose DD mode, you are undoing any signature verification that you previously performed and introducing a potential vector into downloading a malicious bootloader for the installer.


Thank you for your response. Helped a lot. On this quote, where do the two files “go”? Stored elsewhere? Not used at all if DD mode is selected, etc.?

I presume they get stored alongside the Rufus installation, somewhere on your hard drive that’s running Windows.

I would assume once you write an ISO in “ISO” mode, it copies those files to the write destination (USB/CD/DVD), as those files are used once booting from the USB/CD.

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