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I have a working triple boot system using Refit, that is modeled closely after the steps detailed in https://help.ubuntu.com/community/MactelSupportTeam/AppleIntelInstallation, except that I'm using OSX Lion, Ubuntu 12.04 and Windows 7.

EFI + HFS + Linux + swap (hidden from MBR) + NTFS

I am contemplating the creation of more logical partitions (by carving them out of the extended partition) so that I can potentially install newer OSes such as Windows 8 on them while keeping the current ones. I know Linux variants wouldn't have a problem on logical partitions; I'm more concerned about Mountain Lion and Windows 8 and how their presence will affect the current hybrid GPT-MBR tables.

I understand that repartitioning the extended partition in Ubuntu partitions in the working setup, would possibly break the partition tables. Would I have better luck if I were to create all the desired partitions in a fresh system with only Lion installed?

Update:

Right now it looks like I have no choice but to stuff the Windows installations onto the MBRs, and sort out the partition tables after the Macs and Linuxes have been installed. Installation of the second OSX while not a problem, actually changes the numbering of the existing partitions, so those have to be sorted out using gdisk. It was unfortunate that none of the Windows could be put into GPT on such a system, and having two Windows on MBR mean that files cannot be exchanged easily across the three OS families, since there is only one MBR slot left for either OSX or Linux, so this is really a step back from the triple boot. Maybe this is not such a good idea after all.

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The process should be simple install the 4th operating then modify the boot loader to offer the option to boot to that operating system. Just be aware there are boot limitations ( at least with Windows ) on logical partitions. –  Ramhound Mar 29 '13 at 18:07

2 Answers 2

DO NOT, UNDER ANY CIRCUMSTANCES, CREATE AN EXTENDED PARTITION ON A DISK THAT USES A HYBRID MBR!!

Hybrid MBRs are used on most Macs that dual-boot with Windows, and frequently on Macs that dual-boot with Linux. It's virtually certain that you've got a hybrid MBR. Hybrid MBRs cause a lot of pain even when used just with primary partitions on the MBR side, which is the only configuration that Apple's tools will create. If you already have a setup with an extended partition on a hybrid MBR disk, then your configuration is at risk of serious partition table corruption, and I recommend you read the entirety of the hybrid MBR page to which I've just linked, figure out what your partition layout really is, and reconfigure it to be safer. If you don't already have an extended partition on a hybrid MBR, then don't create one.

In fact, in a hybrid MBR configuration, neither Linux nor OS X uses the MBR side of the table; only Windows uses the hybrid MBR. Linux and OS X both use the GPT side of the hybrid MBR, so for their purposes, you can create as many GPT partitions as you like. If you need more partitions in Windows, you can use gdisk to create a hybrid MBR that places up to three partitions in the primary MBR positions. More than that on one disk is not possible without creating an extended partition, which as I say is inadvisable in the extreme.

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Yes you are absolutely correct. In fact my current scheme does not involve any extended partition at all (I was mistaken as I could not remember the reason why I gave up that approach a long time ago, but now I need to have more partitions again). –  prusswan Mar 30 '13 at 20:04

Turns out that I could install up to 6 operating systems (2 from each major family) on such a setup:

(EFI)
Snow Leopard
Mountain Lion
* Ubuntu 12.04
Arch 
(Linux Swap)
* Windows 7
* Windows 8

The asterisks indicate the systems that had to be placed on the MBR. The key is that while the OSX systems can boot on their own, the same cannot be said for the Arch; it relies on the grub2 bootloader on Ubuntu, which means a MBR partition can be used to boot another GPT partition that is not on the MBR! Going by this reasoning, probably more Linux systems can be installed on top of this setup.

PS: It is also a good idea to install gdisk onto the primary operating system (usually OSX, via homebrew) so that it is easily accessible for fixing up the other operating systems if needed.

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Linux doesn't need to boot in BIOS mode (via BIOS-mode GRUB) on a Mac; Linux can boot fine with an EFI-mode boot loader, which eliminates any dependence on the MBR side of the hybrid MBR. In fact, even in BIOS mode, Linux should be fine booting from the GPT side if you add a BIOS Boot Partition; however, there could be some subtle interaction between boot managers and boot loaders that would complicate your life in such a situation. Better to stick with a pure-EFI boot mode, IMHO. –  Rod Smith Apr 7 '13 at 17:58
    
maybe, but I'm not sure if the hardware support would be good enough for EFI-boot Linux (and worth the extra effort), in the case of Windows that is clearly lacking and that has proved to be the most challenging part of the setup. Anyone attempting a similar setup is most welcome to explore a way to boot the Arch through EFI, even though it doesn't look so promising from the information I found. –  prusswan Apr 7 '13 at 18:09
    
Many people, myself included, boot Linux in EFI mode on Macs with no hardware problems. That said, you're correct that there are some model-specific issues. My impression is that they're more the exception than the rule these days, but I don't know of a site with a complete and current list of such issues. If the 3-partition limit in a hybrid MBR is causing headaches, it's certainly worth the effort to try an EFI-mode boot of Linux, or to try using GRUB with a BIOS Boot Partition in place. –  Rod Smith Apr 8 '13 at 18:11

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