A BIOS to UEFI Transformation
A BIOS to UEFI Transformation
by Rod Smith, email@example.com
Originally written: 6/24/2011; last update: 5/1/2012
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You've heard of the Extensible Firmware Interface (EFI) and the Unified EFI (UEFI), and you're curious. Perhaps you're even
desperate: You know that UEFI is the key to booting Windows on a disk larger than 2 TiB, but your computer uses the old-style Basic
Input/Output System (BIOS). Perhaps you're in-between: You're fed up with the Master Boot Record (MBR) partitioning system, but
you can't get Windows to boot from a new GUID Partition Table (GPT) disk on your BIOS-based computer. In any of these cases,
you may be interested in exploring a way to turn a BIOS-based computer into one that at least seems like it's built atop UEFI. This
article outlines how to do this, beginning with some background information, steps needed to set up the software, using the software,
and some final words about problems and possible workarounds to them.
Be aware that the tools and techniques I describe on this Web page are highly experimental. The software might not work at all; in
fact, it could endanger your data! The software works more reliably on Intel CPUs than on AMD models. If you do get it working, it's
likely to be at the cost of some hairs pulled from your head. It won't work as well as a real UEFI-based computer, so if you've got the
cash, you're better off upgrading your computer if you really need UEFI. If it sounds like I'm trying to scare you off, to a certain extent
you're right. Following the advice on this page is not for most people. If you're technically inclined, sufficiently motivated, and up for an
adventure, though, read on!
One final caveat: I'm a Linux person, and some of the preparatory tools described here are built around Linux. If you don't know Linux,
you can still proceed, either finding other ways to do things or using Linux on an optical disc or USB flash drive (I offer some specific
Bridging the Gap
UEFI is the next generation of firmware for PCs. Macs already use the related but slightly older EFI, and most motherboards and
computers introduced since mid-2011 are based on UEFI—even many that aren't advertised as such use UEFI, although they often use
a BIOS compatibility layer by default. (Some are even built with a BIOS core and use UEFI as an add-on stored in the firmware.)
If your computer is based on a true BIOS, though, how can you make it act like a UEFI-based system? The answer is to use a diskloaded UEFI implementation known as the Developer's UEFI Environment (DUET; or sometimes UEFI DUET). This software is a
real, although limited, UEFI implementation that can be booted like an OS from a computer's hard disk. Once it's in control, DUET
provides typical UEFI services to UEFI-based boot loaders and OSes. This sounds straightforward enough, but there are hurdles to be
DUET has historically been used by UEFI developers; it's not really an end-user product. Most importantly, it's available in
source code form from its Sourceforge Web page, but easy-to-install binary packages have been impossible to come by until
recently. (In fact, even today, "easy to install" may be stretching matters a bit.) Download links for the (relatively) easy-to-install
stuff appear later, in Preparing to Use DUET.
DUET currently lacks support for common optical disc filesystems (ISO-9660 and UDF). This doesn't prevent you from
installing an OS, perhaps even from such a disc; but some installers lack the necessary El Torito boot files to boot with DUET,
and some may fail to boot for unknown reasons. This is true of the Windows 7 installation disc, for instance.
A BIOS to UEFI Transformation
On some systems, DUET fails to detect optical discs, even if they contain appropriate El Torito boot files or if you've loaded an
ISO-9660 driver. This happens with the laptop computer on which I did most of my initial testing, for instance. If you run into
this problem, you'll need to copy at least the initial OS boot files to a USB flash drive or hard disk to start an OS installation.
DUET requires a series of boot loaders to boot. The software has traditionally been booted from floppy disks or USB flash
drives, but it's now possible to install it to boot from a hard disk.
Existing OS installations may not work if you try to boot them using DUET (or if you switch boot modes on a UEFI
motherboard, for that matter). Some, such as Linux, can be fairly easily set up to boot either way. Others, such as Windows,
have awkward conversion procedures.
Some computers don't work with DUET. Most importantly, it's really only useful on 64-bit x86-64 computers, especially in
binary form. In fact, it doesn't start up properly even on some x86-64 computers. In tests on five x86-64 systems, I managed to
get one or both versions working on just three computers—a pretty dismal success rate, really. It may just be coincidence, but
the two computers that worked best for me used Intel CPUs, whereas the two that worked worst and the one that worked with
version 2.1 but not version 2.3 all had AMD CPUs.
Many OSes have limited or no UEFI support. Windows can install pretty easily using UEFI, but support in Linux is spotty (but
improving). I haven't tried FreeBSD yet, but I understand it's got pretty weak UEFI support. Really, your best reason for running
DUET is to use Windows or a Windows/Linux dual-boot. (Hackintosh configurations are another matter, and another can of
worms! I don't cover them here.)
Because of these limitations, I recommend proceeding slowly with DUET. Installing the software to a USB flash drive or a spare hard
disk will enable you to test if the software will boot at all. If it doesn't, you can abandon the project without wasting too much time or
endangering your existing installations. If DUET boots, you should do a test installation or two to a spare hard disk before performing a
"real" installation. That way, if you run into problems, you'll know what they are and can either learn how to work around them or stop
before you endanger your existing OS installations.
There are several ways to configure a computer to use DUET. You can use it for some or all of your computer's OSes. For instance,
you might use DUET to boot Windows from a GPT disk, but leave Linux booting in BIOS mode, since it can boot fine from a GPT
disk even on a BIOS-based computer. You can boot DUET from a hard disk or from a USB flash drive. If you use it to boot
Windows, you should be aware that Windows must be installed to a GPT disk when you use UEFI (including DUET)—but that may
be the point of using DUET! If you have more than one disk, you can mix GPT and MBR disks.
Preparing to Use DUET
So, are you ready to proceed? You'll have to download several items. All of them are open source software, with the exception of
Windows if you decide to install it. The list is:
SYSLINUX—This is the first of the boot loaders you need to boot DUET. (You must follow a few links from the main page to
get to the download page. The download package includes both source code and binaries.) SYSLINUX resides in the MBR,
meaning that it's the first boot loader to be called. In fact, several other boot loaders can be substituted for SYSLINUX, and if
you want DUET to be just one method you use for booting from a hard disk, you might want to use another one, such as GRUB.
The "Managing the Boot Process" section briefly describes some possibilities.
BootDuet—This is the second of two boot loaders you'll need to boot DUET. BootDuet installs in a partition boot record
(PBR)—that is, at the start of a disk partition. This link is a source code package. The DUET package described next includes
compiled BootDuet binaries in its BootSector subdirectory, so you don't really need to download BootDuet separately.
DUET itself—That link is to a page with a binary build of the
package. Click the "Download master as tar.gz" link on the right
side of the page. This link also includes the BootDuet code and
various installation scripts.
A working Linux installation—The instructions I provide
here are based on Linux. If you don't know much about Linux,
you'll have a harder time proceeding, but you should be able to
Note: I know of three independent binary
builds of DUET. The one described here
sticks fairly close to the original source code.
The other two, XPC and Clover, modify the
source code for the purpose of functioning as
Hackintosh boot loaders. Although it's
conceivable that XPC or Clover might work
better on some systems than the version
A BIOS to UEFI Transformation
muddle through. You can use a Linux emergency disc, such as
described here, the installation procedure will
Parted Magic, System Rescue CD, or RIP Linux, to do the
be quite different. XPC and Clover are
Linux-specific tasks. I used version Parted Magic 6.1 as a
intended to be installed from OS X, so using
model when writing these instructions. Since then, the Parted
them on a non-Hackintosh system could be
Magic maintainers have changed to a date-based numbering
scheme. Version 2012_04_21 (the latest as I write this revision)
is virtually identical in the features that are important for purposes of this Web page. It's also possible to install DUET without
using Linux at all, but it becomes more tedious because a critical installation tool, d e - n t l , is a Linux-only script. Without
d e - n t l , you'll need to read the documentation for SYSLINUX, BootDuet, and DUET and install each package
At least one UEFI-capable OS—There's not much point in running DUET unless you've got an OS to install on it. Among the
numerous Linux distributions I've tried on DUET and "real" UEFI computers, Fedora has given me the fewest problems,
although it's still a bit rough. Windows, as noted earlier, installs pretty easily on a UEFI system. Be sure to get a 64-bit version of
your OS, though. One of the limitations of UEFI is that it's difficult, and sometimes impossible, to install a 32-bit OS on a 64-bit
CPU; and because there are few 32-bit UEFI implementations for x86, few OS vendors support UEFI installation in their 32-bit
OSes. Certainly Microsoft doesn't.
In addition to the software, you'll need some hardware items:
A 64-bit computer—Specifically, something that uses an x86-64 (aka AMD64 or EM64T) CPU. Most desktop and laptop
PCs sold since around 2007 qualify.
OS disk space—At a minimum, you'll need your computer's main hard disk. Experimenting in this way is risky, though, so I
recommend you use a spare hard disk. A USB flash drive or similar external storage can be sufficient to boot DUET, which
consumes only about 1.7 MiB, but if a preliminary test with DUET alone is successful, you'll presumably want to install an OS,
and you'll need more space for that.
USB flash drives—Although you can sometimes get by without using one, USB flash drives are very handy for holding your
initial test DUET installations and perhaps for holding copies of your OS installers. This is especially true if DUET fails to detect
discs in your optical drive or if your OS fails to boot from it. Some OS installers will fit on a 4 GB or even a 1 GB drive, but
others may require as much as 8 GB of space.
The ideal situation is to have two computers and one or two USB flash drives. You leave one computer untouched and use another
one, with no valuable data on its hard disk, for experimentation. You can use the main computer to create different DUET
configurations as OS installers on the USB flash drives, which you then use on the test computer. When you find something that works,
you can install DUET on the test computer, removing the USB flash drives from the equation. If you've got just one computer, but have
a spare hard disk, you can unplug your regular disk for safety and use a Parted Magic disc to set up the spare hard disk directly and
test its ability to boot.
If you like virtual machines, you might be tempted to use one for testing. This may work with some, but I've had no luck with DUET
and VirtualBox. This isn't so bad, really, since VirtualBox has its own UEFI implementation. It can't boot Windows, though. I don't
know how DUET fares with VMWare, QEMU, or other virtual environments.
The following instructions assume that you've got a computer with a completely blank hard disk (meaning one with no data you care
about). If this is your regular computer and you're using a spare disk for testing, you should prepare a few things before you begin:
Burn Parted Magic to a blank CD-R. (Alternatively, you can use a Linux installation on another computer, as noted above.)
Unpack the . a . zor . i file you downloaded for SYSLINUX. It should extract into its own directory. If you're using a
regular Linux installation, you can instead install its own SYSLINUX package, in which case you should use your package
system to figure out where its binary files are installed.
Unpack the DUET tarball you downloaded. It should extract into its own directory (t a o o e u f _ u t b i d incr_eide_uls
t a o o e u f _ u t i s a l ras I type; but its maintainer has changed the name in the past, so it may be something else
A BIOS to UEFI Transformation
Copy the SYSLINUX and DUET directories to a USB flash drive. (Alternatively, you can use a regular Linux installation on
another computer and use the USB flash drive as a target for the DUET installation.)
With these preliminaries out of the way, you can begin:
1. Unplug any external disk devices from your target system, including USB flash drives. They'll only confuse matters, and may be
at risk of damage should you mistakenly write data to one of them. If you want to do an initial install of DUET to a USB flash
drive, though, you should leave that one target drive plugged in.
2. Boot Parted Magic on your test system. At the boot loader menu, select the option, "Default Settings (Runs from RAM)."
3. Double-click the Partition Editor icon on the left side of the screen. This launches the GParted partitioning software. The resulting
window resembles Figure 1. Warning: See the "Troubleshooting Problems" section for an important caveat concerning
subsequent uses of GParted.
Figure 1. GParted is a flexible Linux partitioning tool
4. If your computer has more than one hard disk or if you have any removable disks plugged in, select the one you want to use for
testing from the button near the top-right corner of the screen. (It reads /dev/sda (55.89 GiB) in Figure 1.) Note the name
(/dev/sda, /dev/sdb, etc.) of the device; you'll need it later.
5. Select Device -> Create Partition Table from the GParted window. A dialog box appears.
6. Expand the Advanced item and select GPT as the partition table type, as shown in Figure 2. Heed the warning in the dialog box;
if your disk has any data you want to save, click Cancel and rethink your plan. Note that it is possible to convert a disk from
MBR to GPT form non-destructively using my GPT fdisk (g i k c d s , and s d s ) software; however, the disk will be
non-bootable immediately after the conversion. Experimenting with DUET on your hard disk is risky, so try such a conversion
only if you're desperate and if you understand that you may have to re-install your boot OS. I don't describe such conversions on
A BIOS to UEFI Transformation
Figure 2. To prepare a disk for UEFI use, it's best if it's partitioned as a GPT disk.
7. Click Apply to create a new GPT on the disk.
8. Right-click in the large unallocated space and select New from the pop-up menu. You'll see a Create New Partition dialog box,
as in Figure 3. You'll now create an ESP that will both hold your DUET software and function as the ESP for the UEFI and your
Figure 3. GParted enables you to enter new partition data in several ways.
9. Set the New Size (MiB) field to something between 100 and 500. Make it on the large side of this range if you expect to install
multiple Linux distributions and use ELILO or the kernel's EFI stub loader, since then you may need to store your Linux kernels
on the ESP. For most other purposes, something between 100 MiB and 200 MiB should be fine. If you change the value by
typing it, click in another space field to be sure they update correctly.
10. Set File System to FAT32. Note that Windows 7 requires FAT32, not FAT16, in its ESP, so be sure to get the FAT type right!
(On the other hand, Ubuntu creates a FAT16 ESP—but that's a serious flaw that argues strongly for installing Ubuntu in BIOS
mode rather than in UEFI mode.)
11. If desired, type a name into the Label field. This will show up in some tools and can help you identify your partition.
12. Click Add. Your new partition will appear in the display, but it won't actually be created.
13. Click Apply to create the partition. GParted displays a dialog box asking for confirmation; click Apply. After a moment, you
should see a notice that the operation completed. Dismiss it.
14. Note the partition name in the list (on the left of the display). It will probably be /dev/sda1. If there's a triangle with an
A BIOS to UEFI Transformation
exclamation mark in it, don't worry; GParted just can't detect the filesystem, but it will be created later.
15. Right-click the partition you just created and select Manage Flags. A dialog box like the one in Figure 4 will appear.
Figure 4. GParted identifies the ESP by the 'boot' flag.
16. Select the "boot" flag, as shown in Figure 4, and click Close. Unfortunately, GParted uses the same terminology ("boot flag") to
identify an ESP on GPT disks as it does to identify the bootable partition on an MBR disk. The two concepts aren't very closely
related, but we're stuck with the choices of the GParted developers.
17. Click Apply in the main window to write this change to disk.
18. You can optionally create partitions for your OS installation in a similar manner; however, you must be careful, since some OSes
have specific requirements. As a general rule, it's best to let the OS installer create its own partitions.
19. Select GParted -> Quit to exit from the program.
20. Click the icon of a computer monitor. This opens an LXTerminal window, as shown in Figure 5.
Figure 5. LXTerminal is Parted Magic's command prompt; it lets you type commands to do unusual or complex
A BIOS to UEFI Transformation
21. Type l / e / d in the LXTerminal window. (Note that those are forward slashes, / not backward slashes, as Windows
uses.) The result is a list of filenames associated with disk devices. If you've got just one disk, it will contain / e / d (the
whole hard disk), / e / d 1(the partition you created), and possibly / e / d 2and above if you created additional
partitions. Take note of the disks and partitions that are present.
22. Insert your USB flash drive with the DUET and SYSLINUX software and wait a few moments.
23. Type l / e / d again. You should see the entries you saw before plus one or two more. The whole-disk device
(/ e / d , probably) is your USB flash drive. If there's a partition entry, such as / e / d 1 that represents a partition on the
flash drive. If there's no partition entry, it probably means that the disk is a "superfloppy"—that is, that it's being used
24. Type m u t / e / d 1 / n / s , changing / e / d 1to your USB filesystem—change the device letter as appropriate
on dvsb mtub
and change the partition number as necessary or omit it entirely if the disk is used as a superfloppy. If you get an error message,
you may need to experiment or get help. If you're using a disk other than Parted Magic, you may need to select a different mount
point (/ n / s in this procedure) or create / n / s by typing m d r / n / s .
25. Type l / n / s to verify that the files you placed on the USB flash drive are now accessible.
26. Type c / n / s / i n c r _ e i d e _ u l s t a o o e u f _ u t i s a l r changing the pathname if the
DUET package you downloaded uses a different one. (Tip: Linux shells support command completion, so you can type a few
characters and then press the Tab key to have the shell complete a long command or filename.)
27. Type s . d e - n t l - - / n / s / y l n x
h /utisal m s mtubssiu4 5 m r / e / d 1 changing the path to the SYSLINUX
binaries (from / n / s / y l n x 4 5 and to your EFI
System Partition (from / e / d 1 as necessary. The dvsa)
option tells the script to install SYSLINUX, and - tells it
where the SYSLINUX binaries exist.
28. The installation script displays some information about what it's
installing and where it's found things such as the target disk.
Review this information and, if it seems OK, type Yat the D
y u w n t c n i u ( / ) prompt.
o at o otne YN?
Additional options to d e - n t l are
available. Type s . d e - n t l with
no options to see descriptions of all of them.
The most notable options are - d (which
installs a UEFI version 2.1 rather than the
default of 2.3), - (which creates a FAT
filesystem on the target partition), and n
n m (which assigns a name to the FAT
filesystem created by - ).
A BIOS to UEFI Transformation
If the d e - n t l script completes without complaint, chances are it's installed DUET on your hard disk. You can now remove the
optical disc from the drive and either type r b o or select Logout from the menu that pops up from the lower-left corner of the screen
to reboot the computer.
When you reboot, the computer should go through it's usual BIOS startup displays. If you installed to a USB flash drive, you may have
to press F10, F12, or some other function key to get to the boot device selection screen to boot from that drive rather than from your
hard disk. When this is done, you should see a display that reads W L O E T E I W R Dand/or a Tianocore logo. You're likely to
ECM O F OL
then see a UEFI menu, similar to the one shown in Figure 6. (I'm cheating here a bit, since this screen shot shows a VirtualBox UEFI
menu, but the DUET menu is very similar.)
Figure 6. The main DUET screen shows a number of boot and device management menus.
This menu is confusing to the uninitiated, but the most important item for the moment is the Boot Maintenance Manager. Select this item,
followed by Boot From File on the next screen, and you'll see a list of disk devices, as shown in Figure 7. Select one of these and you'll
be able to browse through your disk filesystems to locate and run EFI programs and boot loaders, which have . f filename
Figure 7. UEFI identifies disks using long codes.
A BIOS to UEFI Transformation
If all you've got is a DUET installation, you won't be able to do much, since all it comes with is a shell (command line) program and a
small number of utilities. In practice, you'll want to install an OS, and for that you'll need an OS installer. If you're lucky, DUET will
boot your OS installer when you insert its installation CD, DVD, or USB flash drive and reboot back into DUET. If you're less lucky,
you'll need to copy some or all of the installer's files to a USB flash drive or a hard disk partition.
Installing Windows Under DUET
Theoretically, Windows should install directly from its installation DVD under DUET. In practice, it hasn't worked for me. You might
want to try it, but if it fails, you'll need to copy the Windows boot files from the installation DVD to a USB flash drive or hard disk
partition. In any event, you'll need a 64-bit retail Windows installation disc (I've tested only with Windows 7). I've been unsuccessful in
getting an OEM recovery disc (the type you create by burning the ~20 GB recovery partition to DVD) to work for this purpose. This
site provides download links for various Windows 7 versions. My understanding is that downloading and using such an image is legal
provided you've got a valid Windows license key—but you must download the same version you own (for instance, Windows 7 Home
Premium 64-bit). If your computer came with Windows 7 pre-installed, the key should be on a sticker on the case or in a manual. (It's
on the bottom of my laptop, for instance.)
One important pre-installation note: Windows is fussy about the EFI System Partition. Most importantly, Windows requires that this
partition use a FAT32 filesystem. The procedure described earlier, in "Installing DUET," creates a suitable partition. If Windows
complains that partitions are not in the correct order, or that it can't find the EFI System Partition when one is clearly present, these are
symptoms that you've got a FAT16 ESP. If this happens, you may need to re-create the ESP and ensure that it's FAT32. Alternatively,
you could forego creating the ESP yourself, use DUET on a bootable USB flash drive, let Windows create the ESP, and then install
DUET to the hard disk after Windows is done installing.
With the necessary tools in hand, you should follow these steps (skipping to step #4 if you want to try booting the Windows installation
1. Using any available computer, copy all the files from the UDF side of your Windows installation disc to a USB flash drive. (The
Windows 7 installation disc has both ISO-9660 and UDF filesystems on it. Thus, you may need to adjust mount options to
access the UDF side. The ISO-9660 side holds only a text file stating that you need to have UDF support to access the disc.)
A BIOS to UEFI Transformation
2. Extract the 1 W n o s B o / F / o t g w e ifile from the S U C S i s a l w mfile on the Windows installation disc.
This file is in Windows Imaging Format, which you can extract with 7zip. (I used 7 under Linux.)
3. Place the b o m f . f file on the USB flash drive with your Windows installation files.
4. Boot the target computer into DUET.
5. Using the Boot Maintenance Manager, launch the b o m f . f file. The Windows installer should start up. You can proceed
with installation in the normal fashion; everything will be installed from the USB flash drive. I don't describe Windows installation
in detail on this page. Microsoft has a Web page on the subject. A few quirks remain, though....
6. Partway through the installation, the computer will reboot. If Windows doesn't start automatically, you must use the UEFI Boot
Maintenance Manager to select the E I M c o o t B o / o t g w e ifile from your ESP. This will launch the nearlyF/irsf/otbomf.f
complete on-disk Windows system to complete the installation.
7. On subsequent boots, you may need to select the same E I M c o o t B o / o t g w e ifile when you want to boot
Windows. (See the "Managing the Boot Process" section for information on how to select a default boot loader.) If you're lucky,
though, Windows might boot automatically.
If you've got a working Windows installation on an MBR disk and you want to convert to GPT and UEFI booting, you can do so, but
the process is a bit awkward. See this wiki entry or this thread on the InsanelyMac forum for details.
Installing Linux Under DUET
In principle, Linux installation under DUET works like Windows installation. I've had some luck booting some Linux distributions
directly from optical discs, but only on certain computers—as noted earlier, my main DUET test system has an optical drive that DUET
can't detect. Therefore, the following instructions emphasize installation from USB flash drives. You can try using an optical disc,
though. I begin with some comments common to all distributions. Notes on Fedora, OpenSUSE, and Ubuntu follow....
Common Linux Installation Notes
The libparted library, which is used by most Linux distributions as part of their partitioning procedure, has a bug that causes it to clear
GPT attribute data whenever a partition table is modified. The SYSLINUX boot loader relies on the Legacy BIOS Bootable attribute
to be set, so when the installer reboots, the computer will become unbootable, at least in DUET mode. The solution is fairly simple, but
tedious because it requires booting Parted Magic to make a very simple change:
1. Boot the computer using Parted Magic (or to another Linux distribution in BIOS mode).
2. Open an LXTerminal window.
3. Type s d s - 1 s t 2 / e / d , changing 1to the partition number of your ESP and / e / d to the disk device.
gik A :e: dvsa
Keep 2as a constant; that's the position of the Legacy BIOS Bootable bit in the attributes field. Be sure to pass an uppercase Aoption; a lowercase - won't have the desired effect.
Alternatively, you could install another MBR-resident boot loader, such as GRUB or LILO. These boot loaders don't rely on the
Legacy BIOS Bootable flag, which makes them less susceptible to libparted's damage.
Linux switches easily between BIOS and UEFI boot modes. Therefore, it may be easier to install the OS in BIOS mode and then
reconfigure it to boot in UEFI mode, if desired, rather than to install directly in UEFI mode. For some distributions, this may be your
only practical choice. The last I checked, for instance, Debian didn't support direct installation in UEFI mode on x86-64 computers.
Installing Fedora 15 under DUET
The procedure I used for installing Fedora 16 was as follows:
1. Download a Fedora 16 64-bit DVD image and burn a DVD from it. (The smaller CD image might work, too.)
A BIOS to UEFI Transformation
2. If you use DUET 2.3 on your hard disk, prepare a USB flash drive with DUET version 2.1 (by using the - d option to d e ek
i s a l as described in the sidebar by step #27 in the DUET installation procedure). This step might not always be necessary,
though. I needed to do it because I had problems with Fedora's GRUB under DUET 2.3, but that might have been a systemspecific issue.
3. Copy the E Iand i a e directories from the DVD to a FAT partition on a USB flash drive. Caution: The E Idirectory
includes a file named E I B O / O T 6 . f , which is a name that's often given to a default boot item. If you've installed
another OS, you should be sure to not use the ESP as a target partition for these files, lest you overwrite the default boot loader.
4. Boot the target computer using DUET and enter the UEFI menu.
5. Insert the Fedora 15 DVD into the drive.
6. Select the E I B O / O T 6 . f file from the USB flash drive.
If your system can boot from an optical disc, you might be able to forego step #3. When you boot DUET with the Fedora disc in the
drive, it will then start up directly into the Fedora installer. If you need to use this hybrid flash drive/DVD installation, the the kernel will
load from the flash drive, but most of the files will install from the DVD. If you omit the DVD, the installation will actually complete, but
the installer will require a network connection and will download everything from the Internet. Once launched, the installation process
procedes much as it would on a BIOS-based computer. A complication develops when the computer reboots near the end of the
process, though, because of the libparted bug described earlier, in "Common Linux Installation Notes." Restoring the Legacy BIOS
Bootable attribute fixes the problem and you can reboot DUET.
You might now need to select the e i r d a / r b e iitem in the ESP when you reboot. When you do, GRUB should appear
and boot your Fedora kernel, which will then take you to the final steps of Fedora setup. On my system, Fedora's installer did not
detect my earlier Windows installation, so I had to add it to the GRUB configuration—but this didn't work as well as I'd hoped, as
noted later, in "Managing the Boot Process."
Installing OpenSUSE 12.1 under DUET
I've done one test installation of OpenSUSE 12.1 under DUET. The procedure is a bit more tedious than is the Fedora 16 installation
procedure, but it's much better than was the procedure for OpenSUSE 11.4, which was downright painful. Nonetheless, you might
consider installing in BIOS mode and then converting to a UEFI boot. If you care to try installing directly in UEFI mode, here's how:
1. Download and burn an OpenSUSE 12.1 DVD. If DUET detects and boots your optical disc, you can boot it and skip ahead to
2. The b o / 8 _ 4 e ifile on the installation disc is actually a disk image containing EFI boot files that you must extract if your
system can't boot from the optical disc. Under Linux, m u t - l o / n / d o / o t x 6 6 / f / n / l p ywill
on o op mtcrmbo/8_4ei mtfop
do the trick, provided the disc is mounted at / n / d o and you have an empty / n / l p ymount point.
3. Mount a FAT USB flash drive and copy the contents of / n / l p yto it. The USB flash drive should now have an
e i b o directory with four files.
4. Boot your target computer into DUET's menus.
5. Insert the USB flash drive and the OpenSUSE 11.4 DVD into the target computer.
6. Using the UEFI boot manager, boot the e i b o / o t 6 . f file on the USB flash drive. The OpenSUSE installer should
start up. I won't describe every detail of the installation procedure, but there are a few wrinkles that require explanation....
7. The Suggested Partitioning screen recommends creating a new "boot volume" (aka an ESP), which is unnecessary if you've
already created one as described earlier. Therefore, you should select the Edit Partition Setup option, delete the duplicate ESP,
and reconfigure the installer to mount the existing one at / o t e i When you continue, this should result in a warning to the
effect that you're installing to a partition that's not being formatted. Tell it to proceed.
8. Unfortunately, OpenSUSE, like Fedora, clears the Legacy BIOS Bootable flag from the ESP, so you must re-instate it, as
described in the "Common Linux Installation Notes" section.
A BIOS to UEFI Transformation
9. When you reboot, you should use the UEFI boot loader to boot e i S S / l l . f This launches ELILO, which in turn
boots OpenSUSE. It will perform a few final installation tasks, then show a login screen.
Installing Ubuntu under DUET
Don't even think about installing Ubuntu 11.10 and earlier in UEFI mode. I ran into two very serious problems when I attempted to do
Ubuntu uses GRUB 2 to boot the installer from the installation medium, and I had serious problems getting this to work. It hung
before displaying a GRUB menu when I used DUET 2.3, and under 2.1, it behaved erratically—sometimes it would hang, other
times it would give me an emergency g u >prompt, and still other times it would show me a normal GRUB menu but the
installer would hang while loading. This problem might have been at least partly hardware- or BIOS-specific though; you might
have better luck. I eventually worked around it by adding ELILO to my installation flash drive, but the next problem is worse....
Unbidden, Ubuntu 11.04 and 11.10 replaced my valid FAT32 ESP with a FAT16 ESP. This erased DUET and my ability to
boot Windows and Fedora. (I hadn't yet installed OpenSUSE.) Since Windows insists on having a FAT32 ESP, installing
Ubuntu first may be a bit safer, but not all that much better—any way you slice it, you'll have to undo damage done by Ubuntu's
installer. This bug is documented here, if you care to follow it.
The second of these bugs is reportedly fixed in Ubuntu 12.04, which is due out any day now, as I write, but I haven't attempted to
install its betas on a DUET system. The GRUB issue might well also be fixed. If so, Ubuntu should install fairly cleanly if DUET can
read your optical disc or if you use a UEFI-bootable USB flash drive as an installation medium. If you download a disc image and it
doesn't boot directly, you may need to create a mixed DVD/USB flash drive solution similar to the ones described for Fedora and
Until then, or if you have problems installing Ubuntu in UEFI mode, you may want to install it in BIOS mode and then convert it to use
DUET. When you install in BIOS mode, be sure to create a BIOS Boot Partition or GRUB might not install. GRUB will also overwrite
SYSLINUX in the MBR, so you'll need to create a GRUB entry for your ESP, as described in the "Managing the Boot Process"
section. If you want to preserve SYSLINUX in the MBR, you can try installing GRUB to the Ubuntu root (/ partition or to a non)
boot disk (say, another of those USB flash drives I assume you have lying around), but I make no promises that this will work.
After installing in BIOS mode, you can install a UEFI boot loader, as described in the "Managing the Boot Process" section. Ubuntu
has packages for GRUB 2 in EFI mode (g u - f ), ELILO (e i o and rEFIt (r f t Of course, you can also install any of these
l l ),
e i ).
from non-Ubuntu sources. Note that if you install the g u - f package, it will uninstall g u - c which is required for BIOS-style
booting, so if GRUB 2 is now in charge of your MBR and you want to use GRUB 2 for UEFI-style booting, too, you should install
GRUB 2 in some other way.
Managing the Boot Process
Under UEFI, the distinction between two types of boot programs is important:
Boot managers—These programs present a menu of options or enable users to type commands to boot a particular OS. They
don't actually load an OS kernel, though; they just interact with the user and kick the process down the path a bit.
Boot loaders—These programs load an OS kernel and hand off control of the computer to that kernel.
Popular boot programs in Linux (LILO, GRUB Legacy, and GRUB 2) perform both of these tasks, so many Linux users (myself
included) haven't always clearly distinguished between these two functions. Under UEFI, though, the firmware itself includes—or can
include—a boot manager. Boot loaders can therefore be much simpler, and some of them are. Others (particularly UEFI variants of
BIOS boot loaders) incorporate both types of function.
A further twist on all this is that, although EFI implementations can include good boot managers, many of them don't. DUET's Boot
Maintenance Manager is an example of a relatively crude UEFI boot manager—but even it is really quite capable compared to some
firmware implementations' boot managers. Gigabyte's Hybrid EFI, for instance, provides no options beyond selecting a physical boot
device, like a regular BIOS does.
OS-specific boot loaders and independent boot managers typically appear in directories called E I v n o n m , where vendorname
A BIOS to UEFI Transformation
is the OS developer's name, such as M c o o tfor Microsoft or r d a for Fedora. Because the line between boot managers and
boot loaders can be a blurry one, I summarize them all in one list:
Microsoft's boot loader—This boot loader seems to be
quite simple, but there may be hidden power I don't know
My Managing EFI Boot Loaders for Linux Web
about. As far as I know, it simply boots Windows. This is
page covers most of these boot programs in
fine if Windows is your only OS, but if you multi-boot, you'll
want to use a separate boot manager to select your OS, and
have that boot manager chain-load to this one. The EasyBCD tool is a popular adjunct to the Windows boot loader; however, it
doesn't seem to understand UEFI.
The Linux kernel with EFI stub support—Beginning with version 3.3.0, the Linux kernel has included its own EFI boot
loader. In my experience, this is the most reliable EFI boot loader for Linux, but its newness means that it's not yet supported by
most distributions. (Fedora 16 now includes kernels with this feature, but the distribution doesn't support booting via this
method.) You'll need to install your kernels where the EFI can read them, which may mean a bigger ESP than your distribution
sets up by default. If you're using a kernel that includes this boot loader, though, installing the rEFInd boot manager (described
shortly) can be a good way to manage your boot process.
The EFI Linux Loader (ELILO)—This is the oldest of the Linux EFI boot loaders. In my opinion it second only to the
kernel's EFI stub support in reliability and ease of configuration. ELILO can't chainload to another EFI boot loader—that is, it's
only a boot manager among Linux kernels. Thus, if you use it and want to dual-boot with a non-Linux OS you'll need to use
another boot manager to select your OS. Also, ELILO requires that your kernel be on the ESP or another partition that the
firmware can read. This can require a larger ESP than you might like, particularly if you install several Linux distributions or like
to keep several kernels on hand.
GRUB Legacy—This older version of GRUB doesn't normally support UEFI, but Fedora ships with a heavily modified version
that does. It supports chainloading to other . f files, making this program both a boot manager and a Linux boot loader. I've
had problems getting it to reliably chainload, though, so its utility as a boot manager is questionable. It can boot a Linux kernel
from most Linux filesystems (but not from within an LVM or Linux RAID setup), so it can be used even with a small ESP.
The Grand Unified Bootloader (GRUB) 2—This boot loader is flexible and powerful, but its configuration file is complex and
trouble-prone on UEFI systems, in my experience. I've had the best luck with it under VirtualBox's UEFI implementation; on
both a real Intel UEFI system and DUET, it's flaky and unreliable. It tends to be more reliable when built from source and
installed entirely on the ESP than when installed from the binary packages that Ubuntu provides. GRUB 2 can boot a kernel from
a Linux partition, so its use doesn't add much to the space requirements of the ESP. It can also redirect the boot process to
another . f file.
rEFIt—This boot manager originated in the Mac world, and it's got a few bugs on UEFI systems. (Intel-based Macs use the
older EFI 1.x, whereas non-Mac UEFI-based PCs use the newer UEFI 2.x.) It's strictly a boot manager, not a boot loader.
Thus, it can be a good choice for choosing between Windows and Linux, particularly if you prefer ELILO as your Linux boot
loader. Beware, though: Most rEFIt binaries use a hybrid 32/64-bit format that works fine on Macs but that don't work with
DUET. Ubuntu and Debian both ship with rEFIt binaries that work on UEFI systems; and I've made a version with a couple of
patches available here. Because of display problems when used in the default GUI mode, I prefer to use rEFIt in text mode,
which you can activate by uncommenting the t x o l line in its configuration file. As I write, the last update to rEFIt was
released in March of 2010 (just over two years ago), so it appears that it's been abandoned.
rEFInd—I created this program because of the apparent abandonment of rEFIt. rEFInd is in fact a fork of rEFIt, to take up
where its development left off. Most importantly, rEFInd fixes many of rEFIt's UEFI bugs and adds features to improve its
configurability and usefulness to Linux users. It includes features that help it detect and boot Linux kernels that incorporate the
new EFI stub loader feature.
If you're using a boot loader that doesn't include its own filesystem drivers, such as ELILO or the Linux kernel's EFI stub loader, you'll
need to place that boot loader program and its support files on a partition that the EFI can read. This can increase the size requirements
of the ESP. One way around this is to use EFI drivers, which expand the range of filesystems that the EFI can read. This can be a
particularly handy trick with the Linux kernel's EFI stub loader. See the Using EFI Drivers page of the rEFInd documentation for more
details on this approach. (Both rEFIt and rEFInd can automatically load EFI drivers, although some specific builds lack this ability.)
In theory, there are various ways to select which boot manager or boot loader runs by default:
A BIOS to UEFI Transformation
You can put a boot loader in the E I b o directory and give it the name b o x 4 e i
You can write a startup script called s a t p n hand place it in the root of the ESP. A one-line script that simply launches
your desired boot loader can work well.
You can use the UEFI menu's Boot Options menu under the Boot Maintenance Manager to add, delete, and manage entries in
the UEFI's own boot manager, which you can access from the Boot Manager menu.
You can use the Linux e i o t g program to manage UEFI boot manager options, including setting a default. This doesn't
always seem to work quite right, though.
Unfortunately, the last two methods don't work with DUET in practice, although they (or their equivalents) do work with most UEFI
implementations built into motherboards. In practice, the best way to launch your chosen boot manager is generally to name it
If you want to boot both Windows and Linux on a GPT disk, you have two choices: You can boot both using DUET or you can boot
Windows using DUET and boot Linux in BIOS mode. The latter is likely to be slightly faster and is simpler in many ways. Booting
Linux via DUET offers few practical advantages. The most compelling reason might be that you can use rEFIt or rEFInd, which provide
flashier graphical boot menus than do LILO and GRUB. If you use rEFInd with 3.3.0 or later kernels, kernel management tasks can
also be simpler. Still, these advantages are unlikely to outweigh the greater complexity of the initial setup or the extra boot time it takes
to launch DUET.
With that in mind, You may want to consider creating a slightly different configuration than the one described on this page. The
instructions presented earlier, under "Installing DUET," configure the computer to always boot in UEFI mode—at least, when the
computer boots from its hard disk. If, however, you install a standard BIOS-mode Linux boot loader, such as LILO (not ELILO),
GRUB Legacy, or GRUB 2, to the disk's MBR, that boot loader will replace SYSLINUX. You can then add an entry to the MBR
boot loader to chainload to BootDuet, and therefore to DUET. The result will be an initial boot menu that gives you the option of
launching Linux in BIOS mode or DUET; if you select the latter option, you can configure it to launch Windows directly or to launch
another UEFI boot loader. In fact, it's possible to boot the same Linux distribution both ways without any reconfiguration; you just
select whichever set of boot loader options are required to boot in the desired way!
An example of a GRUB Legacy (/ o t g u / e u l tor / o t g u / r b c n entry to boot DUET from an ESP on the first
partition of the first disk is:
Note, however, that not all versions of GRUB Legacy support GPT; you need a version that's been patched with GPT support. (Most
distributions ship with such patched versions.) An equivalent configuration for GRUB 2 (in / o t g u / r b c g although
placement in / t / r b d 4 _ u t mand then regenerating g u . f is preferable) looks like this:
Note that it's possible to create multiple DUET installations and boot them independently. This might be handy if you need to use
version 2.1 for some purposes and 2.3 for others. You might also be able to install related utilities, such as DUET-based Hackintosh
boot loaders, to coexist with the version described here; however, I've never attempted such a configuration.
DUET is still very much an experimental/hobbyist tool. I don't recommend using this solution in a production environment, particularly
not if you lack the technical knowledge required to keep it working. The software might not install and work correctly, and if it does,
DUET installations can be delicate, so you must be cautious about using and reconfiguring them. Some things that can go wrong, and
possible solutions, include:
A BIOS to UEFI Transformation
As noted earlier, DUET works best on computers with Intel CPUs; it fails to run, or runs poorly, on most computers with AMD
CPUs. I don't know the root cause of this problem, and unfortunately I lack a solution.
Sometimes one DUET version works when another one doesn't work. The DUET package described on this page ships with
both 2.1 and 2.3 implementations. The d e - n t l script installs the 2.3 implementation by default. This version is faster and
more capable than the 2.1 version, so it's generally preferable; however, if it crashes your computer, you can give the 2.1 version
a try. You'll need to use d e - n t l to re-install the software, but this time pass - d along with the other options. (You
don't need to completely repartition the disk; just skip ahead to the d e - n t l stage.) Note that the 2.1 version lacks
support for AHCI hard disk mode, so you may need to disable this support in your BIOS. (I saw AHCI drivers in a Hackintosh
XPC package, but I don't have a link handy; and using such drivers would require loading them from a non-AHCI disk such as a
USB flash drive or a PATA disk.)
DUET stores its settings in a file called E i a . i in the ESP. If this file becomes corrupted, DUET may malfunction. In such
cases, deleting the file can solve the problem, at the expense of removing customizations. You may also need to delete this file if
you install DUET on a USB flash drive and intend to move it from one computer to another; the settings for one computer can
cause another to malfunction. The keyboard may be unresponsive on the second computer, for instance, until this file is deleted.
The GParted utility, used here to perform initial partitioning operations, has the unfortunate habit of zeroing out GPT attribute
fields on all partitions whenever the tool makes modifications to any partition. This is a problem because SYSLINUX relies on
one such field, the Legacy BIOS Bootable attribute, to identify which partition should be booted. Thus, if you use GParted on a
working disk, it may stop working. One fix when this problem occurs is described earlier: In a Linux installation, type s d s gik
A 1 s t 2 / e / d , changing 1to the partition number of your ESP and / e / d to the disk device. Another solution is
to replace SYSLINUX with GRUB or some other boot loader that doesn't rely on partition attribute flags. You can also avoid
the problem by using GPT fdisk (g i k c d s , and s d s ) for partitioning and text-mode tools such as m f for filesystem
maintenance rather than rely on libparted-based tools such as GParted.
If you use GParted or some other utility to move the partition to which BootDuet is installed, it may stop working. This is
because the program relies on a hard-coded value of the partition's location on the disk in the FAT filesystem data. If the
partitioning tool doesn't update this field, BootDuet will fail. You can either run d e - n t l to re-install everything (which is
easy but overkill) or adjust the settings, as described in BootDuet's own documentation.
I haven't yet tracked down the precise cause, but I've seen DUET fail to boot when a GPT disk's protective MBR isn't to its
liking. Replacing the protective MBR fixes this problem. (The g i kprogram can do this; use the noption on the experts'
This isn't a DUET issue specifically, but because Linux and Windows use the same partition type GUID to identify their
filesystem partitions, Windows will see Linux filesystem partitions as unformatted Windows partitions; they'll show up in the
Computer window and, if you click them, Windows will prompt you to format them. This is a disaster waiting to happen. I
recommend you change the type code of Linux filesystem partitions using g i k See this page for more on this issue and
solutions to it. The simplest of these solutions is to use a recent version of g i k which provides a Linux-specific partition type
My page on EFI boot loaders for Linux provides much more information on this topic.
The DUET source download page may be of interest if you want to try your hand at building DUET yourself.
My GPT fdisk (g i k c d s , and s d s ) documentation provides information on these partitioning tools, as well as on GPT
The "Windows x64 BIOS to UEFI" article describes how to switch to UEFI boot mode without reinstalling.
This forum thread discusses development of BootDuet and of DUET. (It's the original genesis of the preceding wiki article, too.)
Several additional UEFI links appear here.
Intel has a Web page that summarizes UEFI shell script commands.
A BIOS to UEFI Transformation
The Wikipedia article on UEFI provides a good introduction to what UEFI is and how it interacts with other software and
hardware on the computer.
Microsoft's Windows and GPT FAQ is focused on GPT, but often touches on UEFI's interactions with GPT. Note that it's
overly pessimistic about some topics, such as the possibility of doing MBR-to-GPT conversions without losing data, since they
don't provide tools with the functionality of GPT fdisk.
Microsoft's UEFI and Windows page provides a link to a . o xfile with basic information on UEFI and how Windows
interacts with it.
iBoot is another derivative of DUET; it's intended as a Hackintosh boot loader.
This page describes the EFI boot process.
This page describes the boot process used by Windows Vista and Windows 7, with an emphasis on the post-firmware part of
Clover is a Hackintosh boot loader for BIOS-based computers that includes, among other things, its own build of DUET and a
fork of the rEFIt boot manager. Binaries aren't available from the Clover Sourceforge page, but you can obtain them as links in
this forum thread.
Like Clover, XPC is a Hackintosh boot loader built atop DUET. It's an earlier effort, but I know less about it.
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