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Using BIOS+GPT On Lunar


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#1 Guest_hollowface_*

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Posted 23 December 2014 - 07:48 PM

I decided to re-install Lunar 1.7.0 on a GPT (GUID Partition Table) instead of MBRPT (Master Boot Record Partition Table) even though the virtual machine I'm using employs BIOS not UEFI. I just wanted to gain the experience of doing it. For the purposes of this virtual machine MBRPT (aka ms-dos partition table) suits me fine. If you've never done a GRUB2 installation under such circumstances, then you may not be aware that a dedicated partition is required, I certainly wasn't. Anyways, I just thought I'd share this to aid others who might be thinking of doing it.

My understanding is that the reason a dedicated-bios-boot-partition is required by GRUB2 is that on MBRPT formatted drives there is 446 bytes of space in the MBR. This space is divided into 218 bytes for bootstrap-code, 6 bytes for the disk time-stamp, and another 222 bytes for bootstrap-code. On GPT formatted drives the protected MBR consists of just a bootstrap-code area; larger bootloaders (like GRUB2) that need both bootstrap-code areas won't fit.

Googling around, it seems 1 MiB is the recommened minimum size for the dedicated-bios-boot-partition though using one larger is highly promoted. The reason given for this is that you may outgrow the 1MiB, but this doesn't make any sense to me given that normally bootloaders only get 440 bytes of space in the MBR. To be safe I made mine larger than 1 MiB.

Steps:
1. Install as normal till you get to the drive formatting options.
2. Choose "GPT" as the partition table type.
3. Choose your desired partitioning tool; I used "cfdisk".
4. Create a 10MiB primary partition, and set (flag) type as bios-boot (if you choose a different tool it may have a slightly different name. For example in Parted its called "bios_grub".).
5. Create your normal OS partition(s) and other partitions as desired, and continue on with the installation process.

Easy enough, right?



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