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Old 13th July 2014
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jggimi jggimi is offline
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Join Date: May 2008
Location: USA
Posts: 6,387

Originally Posted by cravuhaw2C View Post
Firstly, what is meant by "MBR" partition? Does it mean the same as MSDOS partition?
A Master Boot Record is a block containing a very small boot program, and contains a partition table that can define up to four primary partitions. See for further information.
There can be only one unique MBR on a single HDD or SSD with single or multiple installed OSes.
Correct. There is only a single MBR. However, the standard was later enhanced to support extended partitions. This was accomplished by chaining additional boot records to describe them. See for further information.
Secondly, what are those 5 architectures that use MBRs? I know Microsoft Windows, Linux and BSD. What are the remaining 2 architectures?
I'm referring to hardware architectures, not software. And the count is currently 6, having just checked the source code: amd64, i386, landisk, loongson, macppc, and socppc. (The cats architecure used it too, but that is no longer supported.)
Sorry but I thought partition 2 was used by Ubuntu while partition 1 was used to store Grub2.
From the table you provided above, you have four primary partitions:
  1. Partition 0, type 83 (linux files), 58,591,232 512-byte sectors, or 28,609 Megabytes.
  2. Partition 1, type 83 (linux files), 87,889,920 512-byte sectors, or 42,915 Megabytes.
  3. Partition 2 - empty
  4. Partition 3 - empty
Would you like to write a short wiki on how to prepare partition 3 with 45 GB for OpenBSD that includes system files, /root, /home, /temp, /var, /usr?

I would appreciate your help in this very much and you can even make it into an FAQ on the official OpenBSD website.
Thanks for your advice. The SSD I'm using is a spare one, used primarily for testing out Linux distros. I'm using it to learn about OpenBSD for now.
My recommendation is not to multiboot. You need to learn to crawl before you walk, and walk before you run. You're asking for flying lessons.
Originally Posted by cravuhaw2C View Post
Thank you for your help and patience all this while but I'm technically challenged.

It would be good if you could write a short wiki on how to install OpenBSD in a multi-boot environment with the following parameters:
  • the first partition is already taken up by a Linux distro
  • the partition for OpenBSD installation will contain all the system files, /root, /temp, /home/, /usr/, /var
No texts I have written has ended up in the FAQ, nor do I expect them to. (I have submitted patches to correct FAQ errors, but that is different.)

Herewith, your flying lesson. It starts with a preflight check at step 1.
  1. Back up your Ubuntu system. You are likely to lose it, or overwrite a critical component rendering it unusable without deep technical skills at best.
  2. Boot the OpenBSD installation media. This is the RAMDISK kernel, which has a very limited set of tools for installation or rescue built-in, and requires no external drives to function.
  3. Run the installation script, from the prompt you receive at boot.
  4. When prompted, edit the MBR. This will put you into the fdisk(8) program.
  5. Having previously done some calculations, begin your OpenBSD MBR partition at sector 146496735, which happens to be the first sector (if I've done the math right, and I may not have) of Cylinder 9119: the address Cylinder 9119 / Head 0 / Sector 1 for the "geometry" indicated by your MBR. These geometries have been virtual, and meaningless for everything except BIOS programs, for decades. But generally, MBR partitions should begin on Cylinder boundaries to prevent BIOS boot issues.
  6. Edit partition 2 or 3. Set it to type A6. Set the size of the MBR partition however you like. Flag the partition active. Then, exit the fdisk program and return to the script, either by w/q or q and answering the prompt to write positively.
  7. You can use the automatic sizing of individual disklabel partitions as offered by the disklabel program, called next by the script. Or, you can configure the OpenBSD disklabel partitions however you wish.

    Note: Depending on the BIOS of your hardware, you may not be able to boot OpenBSD at all. See FAQ 14.8 regarding BIOS boot limitations.
  8. Assuming you are successful, you can then set up a multiboot bootloader, either from within Ubuntu, or within OpenBSD. I used to use GAG, but that has not been supported in years, so now I use grub, which I install as an OpenBSD package.

Last edited by jggimi; 13th July 2014 at 07:23 PM. Reason: typo. again. this time just a misplaced comma and a misspelling of ubuntu.
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