How can I change/convert a Ubuntu MBR drive to a GPT, and make Ubuntu boot from EFI?
Table of contents:
- Terminology
- Converting
- Configuring (+ Dual boot)
Terminology
BIOS = Basic Input/Output System
(U)EFI = (Unified) Extensible Firmware Interface
MBR = Master Boot Record
GPT = GUID Partition Table
UEFI / EFI / BIOS = Firmware interface
MBR / GPT = How the computer knows (per hard disk) what partitions are on the drive and how to boot from them.
UEFI / BIOS
A firmware interface is the way that the firmware (the software inside devices) and operating system interact. It initialises the hardware then runs the operating system and ensures that the operating system drivers can operate the hardware.
The BIOS has been the usual firmware interface that has been used. The UEFI is a newer interface that has several features, such as being faster, having a GUI and being able to start the network card and get an ip address. UEFI replaces EFI. (Those developing EFI saw that there were others doing something similar and so joined them, bringing the ideas of EFI with them. This then became UEFI).
A BIOS requires the bootloader to be at the start of the disk, however a UEFI uses a partition for this and can choose among multiple boot loaders to use.
MBR / GPT + GRUB
The MBR is a section of code at the start of the disk that contains a boot loader (for the BIOS), as well as the partition map and a unique disk identifier.
To install GRUB onto a disk with a MBR, GRUB places a small program in the MBR to load the rest of GRUB from another part of the disk. (This is done because the MBR is too small to contain all of GRUB). The space that is chosen is space between the MBR and the first partition, which usually exists.
GPT is a standard for how the partitons are specified. It does have a 'protective' MBR, however this is only for allowing BIOS based computers to boot and stop tools that only know about MBR from trying to trash GPT. It can have
(How GPT is handled depends on whether it is booting using a BIOS (or UEFI system in BIOS emulation mode) or UEFI. I will focus on UEFI as it relates to the question).
Boot loaders for operating systems are stored in a partion called EFI System Partiton, that is formatted (usually) with FAT32. This is where GRUB is installed.
Converting
First...
We are playing around with the partition table, so guaranteed safety is not possible. It is a risky operation. However, the method should not lose data.
Others coming across this: Do not use on Apple Macs.
Now...
You will need to do this on a live CD (or another linux installation installed to a different disk.)
When dealing with GPT disks, we need to use a GPT aware program. 'GPT fdisk' is
a good tool to use and what I will be using. It can be called gptfdisk or
gdisk depending on distribution (Ubuntu calles it gdisk). Parted (and Gparted)
is also GPT aware, so can 'safely' be used with GPT disks.
To convert you need to:
- Resize partitions to fit GPT data and EFI system partition.
- Convert the disk and add partitions
- Install GRUB to EFI system partition.
1) Resize partition
Use parted (command line) or gparted (GUI) to resize the first and last
partition. The first partion should have about 200MiB before it, and the last
partition should have 1MiB to 2MiB (either will do) taken off the end.
2) Convert the disk
Run
gdisk /dev/sdx
changing the device you want to convert is /dev/sdx.
It should tell you that it will convert the partiton table.
GPT fdisk (gdisk) version 0.6.14
Partition table scan:
MBR: MBR only
BSD: not present
APM: not present
GPT: not present
***************************************************************
Found invalid GPT and valid MBR; converting MBR to GPT format.
THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by typing 'q' if
you don't want to convert your MBR partitions to GPT format!
***************************************************************
Command (? for help):
Now add a new partition, making it of type 'EFI system'. It should find the free space at the beginning (I suggest some low sector number like 34) and automatically use all the free space. The examples use a 4GB USB flash drive with 1 partition already on there, resized as per above.
Command (? for help): n
Partition number (2-128, default 2): 2
First sector (34-7831518, default = 34) or {+-}size{KMGTP}:
Information: Moved requested sector from 34 to 2048 in
order to align on 2048-sector boundaries.
Use 'l' on the experts' menu to adjust alignment
Last sector (2048-421887, default = 421887) or {+-}size{KMGTP}:
Current type is 'Linux/Windows data'
Hex code or GUID (L to show codes, Enter = 0700): L
0700 Linux/Windows data 0c01 Microsoft reserved 2700 Windows RE
4200 Windows LDM data 4201 Windows LDM metadata 7501 IBM GPFS
7f00 ChromeOS kernel 7f01 ChromeOS root 7f02 ChromeOS reserved
8200 Linux swap 8301 Linux reserved 8e00 Linux LVM
a500 FreeBSD disklabel a501 FreeBSD boot a502 FreeBSD swap
a503 FreeBSD UFS a504 FreeBSD ZFS a505 FreeBSD Vinum/RAID
a800 Apple UFS a901 NetBSD swap a902 NetBSD FFS
a903 NetBSD LFS a904 NetBSD concatenated a905 NetBSD encrypted
a906 NetBSD RAID ab00 Apple boot af00 Apple HFS/HFS+
af01 Apple RAID af02 Apple RAID offline af03 Apple label
af04 AppleTV recovery be00 Solaris boot bf00 Solaris root
bf01 Solaris /usr & Mac Z bf02 Solaris swap bf03 Solaris backup
bf04 Solaris /var bf05 Solaris /home bf06 Solaris alternate se
bf07 Solaris Reserved 1 bf08 Solaris Reserved 2 bf09 Solaris Reserved 3
bf0a Solaris Reserved 4 bf0b Solaris Reserved 5 c001 HP-UX data
c002 HP-UX service ef00 EFI System ef01 MBR partition scheme
ef02 BIOS boot partition fd00 Linux RAID
Hex code or GUID (L to show codes, Enter = 0700): ef00
Changed type of partition to 'EFI System'
You should now have the EFI partition.
Command (? for help): p
Disk /dev/sdd: 7831552 sectors, 3.7 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 669247F2-37F7-4797-98F9-9CE56F7EA8C8
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 7831518
Partitions will be aligned on 2048-sector boundaries
Total free space is 4029 sectors (2.0 MiB)
Number Start (sector) End (sector) Size Code Name
1 421888 7829503 3.5 GiB 0700 Linux/Windows data
2 2048 421887 205.0 MiB EF00 EFI System
Then exit gdisk
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed, possibly destroying your data? (Y/N): y
OK; writing new GUID partition table (GPT).
The operation has completed successfully.
Now use Gparted (or command-line mkfs.vfat -F 32 /dev/partition) to format the partition as FAT32.
3) Install GRUB
This comes with less assurances that the previous part as I have not tried it myself.
I am not sure about this step, so I'll guess using RAOF's instructions:
To switch to grub-efi you'd want to
- Find your EFI partition; mount it in /boot/efi. Add this to /etc/fstab¹
- Install the grub-efi package
- Switch your BIOS boot priority from UEFI and Legacy to UEFI only (or a similar option)
You should work out which version of grub-efi to install with
ioreg -l -p IODeviceTree | grep firmware-abi
If it says EFI32 install the grub-efi-ia32 package, if it says EFI64
install the grub-efi-amd64 package. You can install the packages with
sudo apt-get install <package name>
This will probably only work if you have booted in EFI mode.
If it does not work, you could try these step by step instructions
(under "Install GRUB2 in (U)EFI systems") once grub-efi is installed.
Configuring (+ Dual Boot)
If RAOK's instructions work, you should be able to add the following line to
/etc/grub.d/40_custom
menuentry "Windows 7" {
set root='(hd0,gpt1)'
chainloader /EFI/microsoft/bootmgfw.efi
}
It assumes that Windows is recognised as hd0 by GRUB. It may need to be changed
to hd1 in order to work.
Now run
update-grub
to update the config file.
References and further reading
I used several sources.
- Rod Smith's "GPT fdisk tutorial". Good for more info.
- Wikipedia pages for UEFI, BIOS, MBR and GPT.
- Ubuntu's UEFI booting wiki page. Good for more how-to if you get stuck.
- UEFI's own about page.
This answer is incomplete; I've not tested any of this. It's unlikely to eat any of your data, but you have been warned!
What I would guess is happening here is that your BIOS is preferentially booting from legacy MBR, so poor old UEFI Windows 7 is getting overlooked.
One of the nice things about UEFI is that you should no longer need to worry about Windows overwriting GRUB; they should both coexist nicely on the EFI partition. One option would therefore be to switch to grub-efi. Note: I'm unsure whether grub-efi understands MSDOS-style partitions; I think it does. If it does not, this will fail to boot, and you'll need a LiveCD to recover. In fact, have a LiveCD handy anyway!
To switch to grub-efi you'd want to
- Find your EFI partition; mount it in
/boot/efi. Add this to/etc/fstab¹ - Install the
grub-efipackage - Switch your BIOS boot priority from
UEFI and LegacytoUEFI only(or a similar option)
That should leave you with a UEFI-booting Ubuntu install. If it does not, boot up your trusty LiveCD (or Ubuntu Alternate install CD - the “Fix a broken system” option is what you're after ☺), chroot into your system, and install grub-pc again.
¹: More detail for this step: You'll need to find what the Linux kernel calls your EFI system partition. This will be something like /dev/sda2, /dev/sdb3, or such². You'll then need to make the /boot/efi directory, and add a line to /etc/fstab. If your EFI partition is /dev/sdb3, then you would add the following line:
/dev/sdb3 /boot/efi vfat defaults 0 1
Once you run sudo mount /boot/efi you should then find that /boot/efi contains a EFI directory, with a subdirectory for Windows 7.
²: Since you've got multiple hard drives it might be a good idea to find out the UUID of the partition, as that will be stable under addition/removal of harddrives whereas the /dev/sda2 name is not guaranteed not to change. This can be done after you've finished setting everything else up, though.
You can find the UUID by looking in /dev/disk/by-uuid. For example, I get:
$ ls /dev/disk/by-uuid -lah
total 0
drwxr-xr-x 2 root root 100 Dec 5 09:12 .
drwxr-xr-x 6 root root 120 Dec 5 09:12 ..
lrwxrwxrwx 1 root root 10 Dec 5 09:12 27fae347-4c7f-45cb-92d6-5f3d410599a1 -> ../../sda3
lrwxrwxrwx 1 root root 10 Dec 5 09:12 4405-64C8 -> ../../sda1
lrwxrwxrwx 1 root root 10 Dec 5 09:12 5243e250-8da5-4fea-aa63-61466022661d -> ../../dm-0
In my case, I know /dev/sda1 is my EFI system partition, so I have
UUID=4405-64C8 /boot/efi vfat defaults 0 1
in my /etc/fstab.
I have my OSs in separate drives, so that GRUB2 wont' get replaced by the Windows Bootloader and viceversa
That's ideal, so you're likely to have at least one primary partition free in the partition table.
Now my question is, How can I change/convert Ubuntu's drive so that instead of using MBR it uses GPT and allow Windows to boot?
You don't have to convert MBR to GPT to do UEFI booting, just create a primary FAT partition, install the grub-efi-amd64-bin package and follow the instructions in Add an ESP to an existing installation with MBR which should work with current releases of Ubuntu.