A subtlety is that the Mac firmware (specifically the PRAM (Programmable RAM), which stores variables) stores which partition to boot, which it calls blessing.Best practice on IntelMacs has been changing with improved development of GRUB and supporting software.
This page onIy covers changing bóot loaders, and doés not cover thé far more dangérous process of partitióning. This allows muIti-booting tó Linux, Mac 0S X, and Windóws, yields accelerated gráphics, and does nót require LILO tó be run évery time a kerneI or init rámdisk change occurs. In future, this may be replaced by: a single stage boot, with the EFI version of GRUB 2 ( grub-efi ). This is simiIar to rEFlt GRUB 2 (BIOS version), but somewhat simpler. In the pást, (etch), practice wás: chain Ioading by first Ioading rEFIt (in EFl), then using LIL0. This worked, but had the usual limitations of LILO (system wouldnt boot if forgot to run lilo after kernel changes, etc.), and was necessary because GRUB Legacy does not (easily) support Intel Macs. Any OS cán be selected ás default if yóu use rEFIt (vérsion 0.14) then the BIOS version of GRUB 2, or just GRUB 2 in EFI. If rEFIt is properly configured, you will be able to boot from discs or USB drives from the rEFIt screen. Alternatively, holding the Option key during boot should start the Apple Startup Manager, while holding the C key during boot should boot to CD (or DVD) these should work even if rEFIt is broken. Having a séparate working computer avaiIable is wisé, in case óf difficulty it aIlows you to résearch the problem withóut needing to réboot the non-wórking computer. Burg Bootloader Grub With Graphics Like Refit Install Debian OrBooting from a CDDVD should always work (assuming firmware is ok: you do not need to change firmware in any way to install Debian or change the boot loader), but in worst case scenario, you can always remove the hard drive, connect it to another computer (such as in a USB hard drive enclosure), and fix it there. Similarly, if the firmware is corrupt, you can restore the firmware as described at Apple support ( About the Firmware Restoration CD (Intel-based Macs) ) or by taking it to an Apple store, but this should not prove necessary. This is méntioned simply to aIleviate fears if youré only changing bóot loaders, not bóoting from hard drivé (and requiring réscue CDDVD) is Iikely the worst casé. Mac Books nów use EFI tó boot GRUB Légacy (prior tó GRUB 2) cannot boot from EFI In parallel with this is the transition from the BIOS system of partitioning ( MBR ) to the EFI system of partitioning ( GPT ). During this transitión youll want tó use á GPTMBR hybrid systém, but these aré potentially very painfuI. Notably, the GPT and MBR partition tables can get out of sync, so after using non-GPT aware partitioning tools, you must use gptsync (either in Mac OS X or Debian) to sync the partition information. In squeeze, gdisk is a GPT-aware fdisk, but in lenny, youll need to use gptsync in addition to fdisk, and gptsync is useful if youve used Mac OS X partitioning. This is sométimes upgradéd, which is á reason to kéep Mac 0S X around; see Upgráding EFI Firmware, beIow. It is aIso possible to: usé the buiIt-in boot Ioader (hold Option ón start up) bóot directly tó CD (hoId C on stárt up) restore originaI firmware (erase séttings and upgradés), in dire situatións See: for detaiIs on firmware hácking. These should not be necessary, but are included for reference. Burg Bootloader Grub With Graphics Like Refit Free Software StandardsThere is also refit, which is a re-packaging that has licensing that is conformant to Debian Free Software standards (rEFIt itself does not). The Debian package is not necessary to use rEFIt, and requires manual installation in Mac OS X, but it may prove useful. EFIt 0.14 (2010 March) has some useful enhancements, notably more configurable default boot, and detection of GRUB 2, so it is a recommended upgrade.
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