Opening up the Apple
- Article 14 of 16
- LinuxUser & Developer, July 2006
With Apple’s conversion to Intel chips well under way, the possibility of running standard Linux distributions on Macs is proving enticing. Rob Buckley investigates to see whether Linux on Mactel is as easy as it sounds
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The other problem EFI presents is lack of support for old BIOS interfaces. Any x86 operating system that expects to be able to make standard BIOS calls to an EFI-equipped PC would find itself not getting the right responses. While it’s possible to wrap an EFI chip with layers that support BIOS calls, this isn’t a mandatory requirement for using EFI and makes the effort required to use EFI even greater.
However, Apple and its customers had been used to the similarly advanced capabilities offered by the PowerPC equivalent of EFI, Open Firmware. To switch to a BIOS-based PC after years of Open Firmware would be a technological step backwards as well as disincentive for customers right from the outset.
With complete control of its own operating system and no other legacy operating systems to support, Apple plumped for a motherboard equipped with an EFI chip – and no BIOS wrapper.
Linux, however, didn’t suffer the same problems as Windows. Linux has been capable of booting using Elilo from an EFI-equipped PC for several years so chances of Linux being able to boot from a Mac were substantially greater. However, Apple had removed all access to standard EFI configuration tools in favour of its own simpler, user-friendly, unconfigurable booter. It wasn’t actually possible to boot from a Linux disk.
It was only a short period of time before hackers at osxbook.com were able to circumvent some of the problems. By downloading Intel’s own EFI tools and using various command line tools, it was possible to convince the iMac’s EFI chip to recognise Linux installer disks. In conjunction with a hacked version of Elilo and the Linux kernel, Knoppix and Ubuntu were soon up and running on an iMac, although only in a minimal and slightly buggy state.
There were still some problems with this. By playing with the EFI chips in this way, it was actually possible to hose the iMac completely. Various hackers actually had to return their iMacs to Apple for replacement as a result of their endeavours, making it unlikely their solution would enter into common usage among Mac users. It also requires heavy technical understanding on the part of the user.
Meanwhile, a similar project was underway at OnMac.net to get Windows XP running on the iMac. Fuelled by a potential reward of $13,000 provided by a group of Mac users, the OnMac team were eventually able to get Windows XP running on their Macs, albeit without graphics acceleration and support for other pieces of Mac hardware, such as the built-in iSight webcam.
At the start of April, however, Apple did the unexpected. It released a tool for installing Windows XP on Intel-based Macs, complete with Windows drivers for most of the Mac hardware. Bootcamp, as it’s called, consisted of several pieces of software. The first and most important was a firmware upgrade. This upgrade installed BIOS support into the Mactel’s EFI chips – at a stroke, this made Linux and Windows XP viable operating systems on the Mac and made their installer disks recognisable as boot options. The next was a dynamic repartitioning tool, included as part of OS X’s diskutil command line program, that took advantage of the switch from the PowerPC disk partition map scheme to Intel’s new GPT scheme to allow Mac users to re-partition their disks without reformatting. Since Windows XP can’t cope with GPT, requiring an old-style MBR partitioning system, Bootcamp also adds an MBR scheme for Windows’ benefit. The third was a tool for automatically burning a set of Windows XP drivers to a CD to provide graphics acceleration, wireless and wired networking and Bluetooth support.
Some hackers have been able to use Bootcamp to install Linux on Mactels without the need for installing or adding EFI support to Linux. Gentoo and Ubuntu have already been installed. A triple boot solution using the EFI support of Bootcamp has proven elusive. Other than diskutil, there is no partitioning software available that can create dual GPT/MBR partition system drives. GPT-based partitioning software wipes the MBR partition, whereas MBR partitioning software can't edit GPT.
Even worse, MBR only supports four primary partitions and GPT does not support extended partitions. Combining these two limitations means that a dual partition system disk can have a maximum of four primary partitions. In addition, Apple reserves the first primary partition for its Bootcamp bootloader. That leaves only three partitions, one for each OS. Hence, it’s not possible to have a Linux swap partition; instead a swapfile is needed. Lastly, Bootcamp expects the Windows “c:” drive to be the last partition present on the drive. If it isn't, Windows setup will crash with a “cannot find hall.dll” error after the first reboot.
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