UEFI Booting Fedora 12 on an Intel DX48BT2

For some time Fedora releases have supported UEFI (more commonly known as EFI) booting on X86-64 platforms. Having some experience of using EFI on IA64 platforms over the years, I decided to test out EFI booting Fedora 12 on one of my systems which is an Intel DX48BT2 (Bonetrail 2) platform that comes with built-in support for EFI booting.

What do I mean by EFI booting an operating system such as Fedora 12? A platform that supports EFI booting does not rely upon a bootstrap program stored in boot record of a hard disk. A boot manager in the platform firmware knows how to read a disk’s partition table and understands the layout of a FAT filesystem which is in a designated partition. The details of the boot manager are implementation defined, but the boot manager is required to be configurable using well-known EFI global variables. For example, the boot manager is required to inspect the BootOrder global variable for a list of boot options. A boot option is one or more EFI global variables of the form BootXXXX. where XXXX is a 4 digit number starting with 0000, that contain the device and path name of a boot loader to load and run, and possibly a set of options to pass to that boot loader. If there is no BootOrder global variable the boot manager is required to check for a default boot loader in a number of specified default locations. The actual name of the default boot loader is architecture dependant, e.g. for x86-64 it is \EFI\BOOT\BOOTX64.EFI.

To enable EFI booting on the DX48BT2 you must change some BIOS settings. The primary SATA controller must be configured to use IDE mode, i.e. the AHCI (Advanced Host Controller Interface) mode must be disabled. Apparently in AHCI mode the SATA controller firmware is part of the CSM (Compatibility Support Module) and does not support an EFI driver. Even on Intel’s latest server boards such as the S5500BC, you still have to use IDE mode if you want EFI booting! If you are using the second SATA controller which controls the Matrix software RAID, you must also disable it as SW RAID is not supported in EFI boot mode. Finally you must enable the UEFI option in the Boot option menu. I also recommend that you select the advanced boot option although it is not mandatory.

I am somewhat familiar with EFI booting a Windows Vista SP2 x86-64 DVD and was surprised to find that I was unable to EFI boot a Fedora 12 x86-64 DVD because, while it contains a /EFI/BOOT/BOOTX64.CONF file, it does not contain a corresponding EFI bootloader, i.e. /EFI/BOOT/BOOTX64.EFI. More about these two files later.

Next, I turned to figuring out the difference between efidisk.img and efiboot.img as what these images actually contain and where they are/should be used for seems to be undocumented (or at least I could not easily find the documentation.) I burned the images onto two separate DVDs and mounted them to have a look at the contents. I could just as easily have mounted the images using a command such as the following and cd’ed into the mount mount to look at the contents.

mount -o loop -efiboot.img /mnt

Here is a listing of the efiboot image.

total 20
drwxr-xr-x. 3 root root  2048 2009-11-08 19:06 .
drwxr-xr-x. 3 root root 16384 1969-12-31 19:00 ..
drwxr-xr-x. 2 root root  2048 2009-11-08 19:06 boot

total 246
drwxr-xr-x. 2 root root   2048 2009-11-08 19:06 .
drwxr-xr-x. 3 root root   2048 2009-11-08 19:06 ..
-rwxr-xr-x. 1 root root    168 2009-11-08 19:06 BOOTX64.conf
-rwxr-xr-x. 1 root root 225633 2009-11-08 19:06 bootx64.efi
-rwxr-xr-x. 1 root root  17488 2009-11-08 19:06 splash.xpm.gz

The file bootx64.efi is actually GRUB v0.97 and BOOTX64.conf is GRUB’s configuration file. It contains a single GRUB stanza, i.e.

#debug --graphics
timeout 5
title Fedora 12
	kernel /images/pxeboot/vmlinuz
	initrd /images/pxeboot/initrd.img

Since no kernel or initrd images are included in the efiboot.img I am unsure of what you can achieve by EFI booting a USB drive or DVD containing this image.

I had better luck with efidisk.img. Here is a listing of its contents:

total 23
drwxr-xr-x. 2 fpm fpm  2048 2009-11-08 19:06 .
dr-xr-xr-x. 3 fpm fpm  2048 2009-11-08 19:07 ..
-r--r--r--. 1 fpm fpm   168 2009-11-08 19:06 BOOTX64.conf
-rw-r--r--. 1 fpm fpm 17488 2009-10-01 12:08 splash.xpm.gz
-r--r--r--. 1 fpm fpm   449 2009-11-08 19:07 TRANS.TBL

total 146866
drwxr-sr-x. 3 fpm fpm      2048 2009-11-08 19:07 .
dr-xr-xr-x. 5 fpm fpm      2048 2009-11-08 19:07 ..
-rw-r--r--. 1 fpm fpm    397312 2009-11-08 19:06 efiboot.img
-rw-r--r--. 1 fpm fpm  27441152 2009-11-08 19:06 efidisk.img
-rw-r--r--. 1 fpm fpm 122544128 2009-11-08 19:07 install.img
drwxr-sr-x. 2 fpm fpm      2048 2009-11-08 19:06 pxeboot
-rw-r--r--. 1 fpm fpm       400 2009-11-08 19:04 README
-r--r--r--. 1 fpm fpm      1106 2009-11-08 19:07 TRANS.TBL

total 26339
drwxr-sr-x. 2 fpm fpm     2048 2009-11-08 19:06 .
drwxr-sr-x. 3 fpm fpm     2048 2009-11-08 19:07 ..
-rw-r--r--. 2 fpm fpm 23540852 2009-11-08 19:06 initrd.img
-rw-r--r--. 1 fpm fpm      265 2009-11-08 19:06 README
-r--r--r--. 1 fpm fpm      659 2009-11-08 19:07 TRANS.TBL
-rwxr-xr-x. 2 fpm fpm  3423296 2009-11-08 19:06 vmlinuz

total 27041
drwxr-sr-x. 2 fpm fpm     2048 2009-11-08 19:06 .
dr-xr-xr-x. 5 fpm fpm     2048 2009-11-08 19:07 ..
-r--r--r--. 1 fpm fpm     2048 2009-11-08 19:07
-rw-r--r--. 1 fpm fpm       84 2009-11-08 19:06 boot.msg
-r--r--r--. 1 fpm fpm      142 2009-11-08 19:06 grub.conf
-rw-r--r--. 2 fpm fpm 23540852 2009-11-08 19:06 initrd.img
-r--r--r--. 1 fpm fpm    14336 2009-11-08 19:06 isolinux.bin
-r--r--r--. 1 fpm fpm     1010 2009-11-08 19:06 isolinux.cfg
-r--r--r--. 1 fpm fpm   160280 2009-11-08 19:06 memtest
-r--r--r--. 1 fpm fpm   390373 2009-11-08 19:06 splash.jpg
-r--r--r--. 1 fpm fpm     2215 2009-11-08 19:07 TRANS.TBL
-r--r--r--. 1 fpm fpm   147728 2009-11-08 19:06 vesamenu.c32
-rwxr-xr-x. 2 fpm fpm  3423296 2009-11-08 19:06 vmlinuz

The contents of /EFI/BOOT/BOOTX64.conf are the same as in efiboot.img but this time the initrd and kernel images actually existed in the specified directory in the image. However there is no sign of the actual EFI bootloader, i.e BOOTX64.EFI. OK, I thought, there must be something I do not understand about how to EFI boot Fedora 12.

After configuring the BIOS to enable EFI booting as discussed above, I rebooted the DX48BT2 with the UEFI version (efidisk.iso) of Fedora 12 in the DVD drive. Unfortunately the system reported that no bootable devices were found. Fedora 12 did not even try and install as would have occurred with a legacy boot mode install. To see what was happening, I used DUET on a USB key to boot into an EFI Shell and checked the DVD filesystem layout. It was, as I expected, correct per the EFI and UEFI specifications but there was no BOOTX64.EFI on the DVD.

I also inspected a dump of the BIOS on the DX48BT2 to see if there were any text strings in the BIOS which might give me a clue as to what the problem might be. There were no relevant text strings. However I confirmed that the BIOS, or at least the parts I inspected, is EFI-based as you can see looking at this dump of the first few bytes of the binary. The first 16 bytes are the EFI capsule GUID, i.e. 3B6686BD-0D76-4030-B70E-B5519E2FC5A0. The character strings are either UTF-16 or UCS-2, i.e. 16 bit character encoding schemes defined in the Unicode specification.

0000000: bd86 663b 760d 3040 b70e b551 9e2f c5a0  ..f;v.0@...Q./..
0000010: 5000 0000 0000 0000 14a0 2600 0000 0000  P.........&.....
0000020: 0000 0000 0000 0000 0000 0000 0000 0000  ................
0000030: 0000 0000 1402 0000 5000 0000 6600 0000  ........P...f...
0000040: ca00 0000 1601 0000 8201 0000 0000 0000  ................
0000050: 2832 0863 2981 1244 1215 9514 5034 4036  (2.c)..D....P4@6
0000060: 1600 0000 0102 6500 6e00 6700 2000 4900  ......e.n.g. .I.
0000070: 6e00 7400 6500 6c00 2000 4400 6500 7300  n.t.e.l. .D.e.s.
0000080: 6b00 7400 6f00 7000 2000 4200 6f00 6100  k.t.o.p. .B.o.a.
0000090: 7200 6400 2000 4500 4600 4900 2000 4600  r.d. .E.F.I. .F.
00000a0: 6900 7200 6d00 7700 6100 7200 6500 2000  i.r.m.w.a.r.e. .
00000b0: 4500 6e00 6700 6900 6e00 6500 6500 7200  E.n.g.i.n.e.e.r.
00000c0: 6900 6e00 6700 0000 0000 6500 6e00 6700  i.n.g.....e.n.g.
00000d0: 2000 4200 5400 5800 3300 3800 3100 3000   .B.T.X.
00000e0: 4a00 2e00 3800 3600 4100 2e00 3200 3000  J...8.6.A...2.0.
00000f0: 3000 3600 2e00 3200 3000 3000 3900 2e00  0.6...
0000100: 3100 3000 3200 3300 2e00 3100 3000 3500
0000110: 3700 0000 0000 6500 6e00 6700 2000 4600  7.....e.n.g. .F.
0000120: 6900 7200 6d00 7700 6100 7200 6500 2000  i.r.m.w.a.r.e. .
0000130: 7500 7000 6400 6100 7400 6500 2000 4200  u.p.d.a.t.e. .B.
0000140: 5400 5800 3300 3800 3100 3000 4a00 2e00  T.X.
0000150: 3800 3600 4100 2e00 3200 3000 3000 3600  8.6.A...
0000160: 2e00 3200 3000 3000 3900 2e00 3100 3000  ..
0000170: 3200 3300 2e00 3100 3000 3500 3700 0000  2.3...
0000180: 0000 6500 6e00 6700 2000 4500 4600 4900  ..e.n.g. .E.F.I.
0000190: 2000 6300 6100 7000 7300 7500 6c00 6500   .c.a.p.s.u.l.e.
00001a0: 2000 6300 6f00 6e00 7400 6100 6900 6e00   .c.o.n.t.a.i.n.
00001b0: 6900 6e00 6700 2000 6d00 6f00 7400 6800  i.n.g. .m.o.t.h.
00001c0: 6500 7200 6200 6f00 6100 7200 6400 2000  e.r.b.o.a.r.d. .
00001d0: 6600 6900 7200 6d00 7700 6100 7200 6500  f.i.r.m.w.a.r.e.
00001e0: 2000 7500 7000 6400 6100 7400 6500 2000   .u.p.d.a.t.e. .
00001f0: 6600 6f00 7200 2000 4200 5400 5800 3300  f.o.r. .B.T.X.3.
0000200: 3800 3100 3000 4a00 2e00 3800 3600 4100  8.1.0.J...8.6.A.
0000210: 0000 0000 0000 0000 0000 0000 0000 0000  ................

I then decided to try booting the DVD from the F10 boot options menu just as I would with a legacy boot install. This started the Fedora 12 install. From there everything proceeded from a user’s perspective as with a legacy boot install except that most of the software packages were downloaded from the Internet rather than from the DVD. Here is how Anaconda set up my hard disk:

dev/mapper/vg_ultra-lv_root /                ext4    defaults        1 1
UUID=4d93d152-2877-4447-92e8-18d668daba01 /boot                   ext4    defaults        1 2
UUID=B75E-CB6E          /boot/efi               vfat    umask=0077,shortname=winnt 0 0
/dev/mapper/vg_ultra-lv_swap swap            swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0

The only difference between a legacy boot and an EFI boot install is that Fedora 12 partitions the disk using GPT (GUID Partition Table) rather than MBR and the first partition, i.e. the partition with a UUID of B75E-CB6E (EFI partition), was formatted as a FAT32 filesystem approximately 200mb in size. All the EFI-related code is on this partition because only type of filesystem that EFI understands is the FAT filesystem. This is the filesystem that you are using when you are in the EFI shell. It is commonly known as the EFI system partition (ESP).

This suggests that Fedora might not be able to do an EFI boot install onto a hard disk with existing MBR partitions which you want to preserve. There are ways of hacking GPT to embed an MBR in the GPT table in order to handle cases where an operating system is expecting to see an MBR but tools like parted cannot handle these hybrid partition schemes and will in many cases mangle the configuration. If you want to experiment with embedding an MBR within a GPT have a look at the gdisk utility. By the way, you do not need to have the EFI partition mounted to run Fedora 12. You could just mount it on an as needed basis if you need to access or change something relating to EFI or edit the bootloader configuration file.

The Fedora 12 installation creates the following directory structure in this partition.

# pwd
ls -al
total 236
drwx------. 2 root root   4096 2010-01-28 16:33 .
drwx------. 3 root root   4096 2010-01-28 16:09 ..
-rwx------. 1 root root    744 2010-01-28 16:33 grub.conf
-rwx------. 1 root root 226825 2009-11-16 11:16 grub.efi

By the way grub.efi is maintained by Peter Jones of Red Hat and is an EFI version of GRUB v0.97 – not GRUB2. The bootloader configuration file grub.conf contains

title Fedora (
	root (hd0,1)
	kernel /vmlinuz- ro root=/dev/mapper/vg_ultra-lv_root  LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet
	initrd /initramfs-

I tried EFI booting into Fedora 12 once the Fedora 12 installation completed. It did not work at all so I decided to use DUET to manually load the Fedora 12 bootloader and see what was going on. The EFI shell command map -r correctly mapped in the systems’s hard disk drive as fs2:. I changed to this device (just like changing drive letters in DOS) and invoked \EFI\BOOT\REDHAT\GRUB.EFI. This started the Fedora 12 EFI bootloader and I was able to get into Fedora 12.

To provide a default bootloader for the platform, I added a BOOT subdirectory under /boot/efi/EFI and copied grub.efi and grub.conf to this directory renaming the files BOOTX64.EFI and BOOTX64.CONF respectively. This time, when I rebooted, the system got as far as trying to EFI boot Fedora 12 but failed with a kernel panic early in the kernel initialization.

Because EFI booting via DUET worked without any problems, I assumed the problem lay in the difference between the DX48BT2 implementation of EFI booting and DUET’s implementation and spent many fruitless hours exploring the differences. For example, no EFI serial device is set up by the DX48BT2 whereas DUET creates one. I also tried the usual suspects, i.e. the kernel command line options noapic, acpi=off, edd=off, but to no avail.

It took me quite a while to find this problem as the DX48BT2 is a very fast system and the kernel panic was early in the kernel initialization process. Some information was displayed on the screen but it was overwritten by the kernel panic details. In fact, it looked like Dracut was the culprit from the screen ouput but this turned out not to be the case. I finally narrowed down the problem by using the kernel command line option boot_delay=100 to slow down the screen output sufficiently for me to locate where in the initialization process the kernel panic was actually occurring. It turned out that the kernel panic has something to do with the Local APIC (Advanced Programmable Interrupt Controller.) What worked for me in the end was the kernel command line option nolapic. After adding this option to the kernel command line in /boot/efi/EFI/BOOT.CONF the DX48BT2 was able to EFI boot directly into Fedora 12. Success at last!

To enable me to better explore EFI-booting on this system, I changed the boot process so that instead of booting directly into Fedora 12 via the GRUB boatloader, the system booted into an EFI shell. I replaced /efi/boot/EFI/BOOTX64.xfi with a copy of the X68-64 version of Shell.efi, deleted /boot/efi/EFI/BOOT/BOOTX64.CONF and added a startup script STARTUP.NSH to do some basic shell configuration work for me. Now when the DX48BT2 was rebooted, I ended up in an EFI shell in the root of the ESP. To boot into Fedora 12, I simply invoke grub.efi from the EFI shell.

I set up the following directory structure in the ESP:

# ls -R /boot/efi/EFI
apps  BOOT grub.conf  grub.efi  boot.nsh

Attrib.efi   Devtree.efi   edit.efi           hexedit.efi     Ls.efi      Mv.efi        sermode.efi     Type.efi
Cls.efi      diskpart.efi  efichk.efi         IfConfig.efi    mem.efi     NShell.efi    SmbiosView.efi  Unload.efi
comp.efi     dmem.efi      eficompress.efi    IpConfig.efi    memmap.efi  Openinfo.efi  stall.efi       Ver.efi
Cp.efi       dmpstore.efi  efidecompress.efi  LegacyBoot.efi  Mkdir.efi   pci.efi       TelnetMgmt.efi  Vol.efi
Date.efi     Drivers.efi   efifmt.efi         Load.efi        mm.efi      Ping.efi      Time.efi
Dblk.efi     Drvcfg.efi    err.efi            LoadFv.efi      mode.efi    Resets.efi    timezone.efi
Devices.efi  Drvdiag.efi   Guid.efi           LoadPciRom.efi  Mount.efi   Rm.efi        Touch.efi


The tools directory contains standalone versions of many of the EFI shell built-ins together with some additional utilities such as diskpart, efichk and efifmt are Microsoft utiliites.

When you EFI boot into Fedora 12, an extra subdirectory appears under /sys/firmware to contain EFI-ralted information. Here is what Fedora 12 reported in /sys/firmware/efi/systab

[root@ultra efi]# cat /sys/firmware/efi/systab

The zero values for MPS and ACPI20 are obviously wrong. I am unsure of BOOTINFO and HCDP. This indicates a problem with the EFI implementation in the DX48BT2 BIOS rather than Fedora 12. Here is what is in this file when Fedora 12 is booted from DUET.


Here is a listing of /sys/firmware/efi/vars

# ls /sys/firmware/efi/vars
main firmware-05a798ea-39ee-40fc-82c5-622582fa634b
recovery firmware-05a798ea-39ee-40fc-82c5-622582fa634b
supplemental recovery area-05a798ea-39ee-40fc-82c5-622582fa634b

The value in BootCurrent-8be4df61-93ca-11d2-aa0d-00e098032b8c is FFFF which is an obviously invalid setting. No other Boot* global variables are made available to Fedora 12 which is strange. Again this indicates a poor EFI implementation in the DX48BT2 BIOS rather than a problem with Fedora 12. All the pre-OS space EFI global variables defined by the UEFI specification are supposed to be made available to the operating system.

Here is a listing of this same directory when Fedora 12 is booted using DUET.


Note the additional Boot* global variables and the TimeOut global variable per the UEFI specification. If I had set BootNext in the DUET bootmanager it would also have been displayed here. If you come from the Microsoft Windows x86-64 world, some of these names for global variables may be unfamilar to you as Microsoft in their infinite wisdom changed the names. In Microsoft’s BCD (Boot Configuration Data), for example, BootOrder is called displayorder and BootNext is called bootsequence.

Besides those issues I have described so far in this post, I ran into a number of other problems with EFI support on the DX48BT2. The first problem is that the UEFI boot option on this platform is visable but totally undocumented and by all accounts Intel will not answer any questions about this feature because it is a desktop platform. This will have to change as 64-bit operating systems become more common in households and hard disks greater that 2 Gib become commodity items.

Another problem is that when you are in EFI boot mode and the BIOS detects an EFI bootloader such as /EFI/BOOT/BOOTX86.EFI, a menu option “[Internal Shell]” is displayed along with other bootable drives when you press the F10 key to select which “drive” to boot off. However, if you select this option the BIOS simply clears the screen and locks up the system. You have to reboot your system to recover from this. I can only assume that this option was intended to load an EFI shell or EFI boot manager but was never actually implemented. Some of the code is obviously there as it detects EFI bootloaders.

Finally, if you turn off EFI boot in the BIOS setup and thus revert to legacy boot, the boot list displayed by F10 still displays any custom EFI boot options created using efibootmgr less the [Internal Shell] boot option – except now you cannot boot any of the options in the boot list. The only way to eliminate these entries from the boot list is to EFI boot back into Fedora 12 and use efibootmgr to delete these entries.

I have read a number of postings in various forums regarding Intel’s EFI support on desktop motherboards. I generally agree with the sentiments expressed – it is quite buggy and not ready for prime time use. It does indeed boot a EFI bootloader off a GPT disk but that is about all it does. Given that Intel has over 10 years experience with EFI, this is quite surprising. At a minimum they need to provide a proper EFI boot configuration manager and a platform setup utility for creating EFI global variables.

The Fedora project should work to enable EFI Booting a x86-64 distribution DVD by providing a boot loader at \EFI\BOOT\BOOTX64.CONF. It is not sufficient in my opinion to use legacy mode to create an installation which is then capable of being EFI booted. I understand the difficulty of supporting both MBR and GPT on a single DVD but the problem is not insurmountable. If this were done, there would be no need for efiboot.img and efidisk.img.

Well, that’s about all for now on this issue. I hope this post will be of some help to others who are considering switching to EFI booting Fedora 12.

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