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Timur Fayzrakhmanov
Asked: 2015-01-29 09:57:28 +0800 CST

Why I need several boot partitions (EFI and bios grub)?

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I'm trying to understand how to properly partitioning the disk for future Ubuntu installations.

The reason: after trying to install Windows 7 alongside Ubuntu, I enabled "Legacy mode" on my HP pavilon laptop's BIOS (I think it is EFI, but it looks like traditional BIOS). For now I've understand that is complicated task to use GPT and EFI on Windows 7. However at the moment it doesn't matter, because my Ubuntu doesn't start, at the startup EFI says that "no operation system have installed, please check the disk". I can successfully start Ubuntu by choosing "boot from EFI file" option and specifying boot file at startup.

Please see the screen shot below. This is how my disk looks like:

enter image description here

I've read these two very helpful topics: efi-boot-partition-and-biosgrub-partition and how-to-use-manual-partitioning-during-installation. But can't find analogical situation.

So the questions are: Can I install Ubuntu 14.10 with only 4 parts: "/", "/boot", "swap" and "/home"? What the partitions are odd here? (in the example above)

boot

2 Answers

  1. Best Answer

    Short answer: What Timur Fayzrakhmanov wrote is right, replace the /boot-partition with an EFI partition.

    What I know or found out:

    • For booting UEFI you need a FAT32 EFI partition, one for each drive is sufficient and can handle several operating systems (this depends mostly on your UEFI firmware).
    • For booting Linux in legacy mode on a GPT drive you need a BIOS-GRUB-partition without any filesystem and flagged as BIOS_GRUB.
    • For booting another legacy operating system from a GPT partition table the general advice is that you need a separate BIOS-BOOT-partition. To my experience and as far as I can remember just installing Windows 7/8 in legacy mode will create the necessary partitions (IIRC MSR, BOOT and OS).
    • The /boot-partition that is sometimes suggested for advanced setups (RAID, Full Disk Enrcyption, etc.) is really just for advanced systems. With UEFI a boot partition for Linux isn't really necessary for advanced setups either, because the EFI partition can be configured hold the kernel and initrd images as well. The gummiboot developers published a specification how they like to see it implemented and published a new version just a few days ago that would combine all the necessary files and configuration in one file.

    So for UEFI and MBR booting you would at least need an EFI partition (all EFI bootable OS) and a BIOS_GRUB partition (GRUB PC manages all legacy OS). Don't remove or reuse any existing MSR partition. You can try to install a Windows 7 EFI loader to the EFI partition with bcdboot, the Windows 8 version has some more improvements like the /f uefi option.

    Booting a /, /boot, swap and /home 4 partition layout from GPT in BIOS as well as UEFI mode is not possible, you need a partition for each mode. However with GPT there is no real limitation.

    I posted further details/instructions in Is it still possible to install Ubuntu to an external harddrive with UEFI?

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  2. To install Ubuntu on GPT drive and UEFI there is must be "EFI boot partition". The other partitions like "/home", "/boot" are optional. For me optimal are the following partitioning:

    1. EFI boot partition
    2. swap
    3. / (root)
    4. /home

    and that's all)

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