IMac Aluminum

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I have written the following in the hope that it may help those investigating the installation of Arch on their iMac. Parts of this guide are specifically written for the Alu' 20" & 24" iMac.

I have an aluminium 24" iMac, on which I have just (at the time of writing) installed Arch 64bit, twice! I had a serious problem logging into Gnome & anything that required the root password failed. I worked around these problems but was never happy with the setup. I think that the iMac aluminium keyboard may have caused the problem, due to it not having a num-lock key, or an LED to indicate num-lock on/off; my passwords were numerical. Of course I may be wrong. My second install was done with an MS Digital Media keyboard & I don't have the above problem, also my ctrl-alt-Fkeys work now.

Deleting OS X?

Some people seriously consider dropping OS X altogether. I personally think that there is a good reason to keep a small OS X partition, as it allows you to be able to do firmware updates. Some people use an external USB or Firewire drive with which to boot OS X for the firmware updates, & I have heard that people have been able to do it via optical drive, from experience I do not know about these other methods.

rEFIt First

In preparation of an Arch (or any other Linux/BSD based OS for that matter) install, the first thing to do is install rEFIt [1] on your OS X partition. It is also possible to edit the refit.conf file so that Arch will be the default boot OS, see here: [2] it's the very last section of the refit.conf, basically you just uncomment legacyfirst. The only other option in refit.conf that most users will want to configure is the timeout number, (which is located quite close to the start of the refit.conf file) by default it is 20 seconds, I set it to 5 seconds.

Partitioning & Filesystems

There are multiple ways to repartition the iMac drive, my favourite (probably because it is the easiest & being graphical it is most likely the safest) is to boot the Ubuntu 7.10 (or later) LiveCD & run GParted from the desktop menu. I have shrunk the OS X, HFS+ partition, created Ext3, JFS & Linux Swap partition, deleted & moved partitions on the iMac using GParted & the Ubuntu LiveCD. Great stuff! The only present limitation that GParted has with the HFS+ file system, is that it can only shrink the HFS+ file system & can not enlarge it. I'm sure it won't be too long & this limitation won't exist either.

Just a note on using GParted, or any other GUI type of partition management tool, it is generally accepted to be good safe practice to only Apply ONE process at a time. What that means for those unfamiliar with GParted (& the other applications of it's ilk) is you can give it multiple instructions which it stores up until you hit the "Apply" button, after which it goes through the instructions one after the other. If this doesn't make sense now, it very quickly will on using GParted.

My iMac partition scheme is as follows:


sda1 ........ *FAT32* ....... 200Mb .... EFI system partition - While the ESP looks like a FAT32 volume, it is actually an EFI file system, which you want to know how to replace before you delete it. This means don't delete it unless you are sure that you know what you are doing, as it may become essential to Apple firmware updates in the future. Currently the ESP is empty & the firmware boots OS X directly!? At least it is only 200Mb's wasted drive space, though more importantly it counts as one of the four partitions that can be seen by Apple's newly adopted GPT partitioning scheme. More on GPT in the following paragraph.

sda2 ......... HFS+ ........... 50Gb ..... OS X - After thinning out OS X some & keeping tools I use plus iWork, CrossOver Games & Guild Wars, I have about 25Gb of free space to play with here, & for the odd game that may arrive in the future (Guild Wars 2). :D

sda3 ......... Ext3 ............ 15Gb ...... / - Arch - there is currently 12Gb free, it is a new install though.

sda4 ......... JFS .............. 30Gb ...... /home - that should be more than enough space for me there, & I can always resize with GParted.

sda5 ......... Linux Swap .... 2Gb ..... swap - rarely if ever used, but I have the space. It is questionable as to whether this partition needs to exist at all.

Having now used Arch on the iMac with 1GB of RAM for some months I deleted the /swap partition, as for my uses it was never needed.

sda6 ......... Ext3 ............ 200Gb ...... /thevoid - storage for video's music, unsafe backup, whatever...

Accessing the Ext2/3 file system from OS X

I have been using the ExtFS for Mac from Paragon-Software, it is a commercial package that is simple to install, configure & auto mounts any Ext2/3 file system partitions in a read/write fashion when you boot up OS X, 10.4.11 or later on an Intel Mac. It has been working superbly for me, to the point that I have reformatted my 200GB partition called /thevoid from JFS to Ext3 to give me access to it from OS X. For anyone interested you can get a trial version on the Paragon-Software website.

There is also a free software application that is apparently somewhat outdated, but works with Ext2/3 & is working with OS X, 10.5, its name is ext2fsx. I have not used ext2fsx so I can't speak about it from experience.

The GPT partitioning scheme that Apple uses

[3] allows OS X to only see 4 partitions, so be sure to install your boot loader i.e. GRUB/Lilo, & any other partition that you may want OS X to see (like a shared FAT32 data drive) on sda3 & sda4, Windows must also be on sda3 or sda4. Partitions beyond Apple's imposed limit of 4 can still be created & used, e.g. Linux Swap, & other partitions, but they won't be accessible by OS X or directly bootable, though I see no reason why a boot loader like GRUB positioned on sda3 or sda4 could not boot other OS's on partitions numbered greater than sda4. This certainly does place limitations on what we can do. If you require more than this scheme will allow you, you could do away with OS X, & set up the drive on MBR only, using an external drive with OS X on it to update the firmware.

So just to sum up on all of this partitioning stuff, if you have need to use sda3 & sda4, be sure to put any swap partitions on a partition number greater than sda4. Also, it is worth considering not using a swap partition at all, as the only computers running Linux/BSD with 1 gigabyte of RAM that use their swap file are doing intensive specialized work such as video editing, sound recording/editing, 3D modeling...

When partitioning is finished you must restart the iMac & re-sync your partitions with rEFIt, which is quick & easy: You choose to start the partitioning tool in the rEFIt boot-menu & follow the very simple instructions there.

rEFIt may prefer to have partitions in numerical order on the drive, i.e. sda1, sda2, sda3, sda4, sda5, sda6 ... & not shuffled. This is unconfirmed, any feedback on the subject will be appreciated.

Then reboot & hold down the C key, or wait as I do for the rEFIt boot-menu to appear & choose to boot the Arch install CD.

Install Arch

I used both the Arch Beginners Guide [4] & the Official Install Guide [5]. I used the Core install from the CD & updated later. (The FTP install is a quicker method as it installs the latest packages directly over the internet.)

The CD install & network setup went perfectly for me. The Beginners Guide has all that was necessary for my install, though I used the Official Guide to further my understanding, as well as other pages in the Arch wiki & elsewhere.

Installing & Configuring X

When installing the Xserver, [6] I installed as though I was not going to use the proprietary ATi drivers (now called Catalyst), this allowed me to use both the vesa & the xf86-video-ati open source drivers. I only did this out of what turned out (at that time) to be a false sense of fear of the approaching fight to get ATi's Catalyst drivers to work.

Having now had a couple of years experience with Arch since I wrote the above, I have learned that Catalyst can be a real can of worms on Arch in particular. This is due to the way that Arch uses cutting edge versions of packages & the rolling release upgrade system. Which can cause there to be occasional incompatibilities between Catalyst & the version of packages that Arch uses.

This problem can be relatively easily side stepped once you know how. I recommend the "Catalyst Bar & Grill" [7] thread in the Arch forum. It is the best place to find out where things are up to currently, before you install Catalyst.

Due to its being deemed too unreliable to be kept in the [extra] repo, Catalyst must now be installed via AUR .

The good news is that the open-source driver support is as I write this, improving dramatically due to AMD having opened up the tech' info' on all of the ATi GPUs, & also of course because of the dedicated team that has been working so hard on implementing this new found knowledge for the open-source community.

I highly recommend using the xf86-vide-ati driver, as the 2D is the best you can get & the 3D is continually improving dramatically. From the stable repo's 3D is very useful right now.

Controlling the screen brightness:

Below is the C code for a little program that adjusts the brightness on many LCD Apple screens (I have been using it now for over 3 years). It is easy to compile & setup using the following instructions.

The instructions follow:

Copy & paste the C code (found below these instructions) to your /home. Save the code as a file, backlight.c

Now open a terminal in the directory where backlight.c is located.

Type the following in the Terminal:

gcc -o backlight backlight.c

You now have a program called backlight. It should adjust the brightness.

To change the brightness, you have to have direct access to video memory, which means that you have to be superuser (root).

Type su, then your root password when prompted.

Now test the program by typing ./backlight 10 in the terminal.

You can give it values from 1 to 15. Find a value you like.

Now enter the following in the Terminal:

cp backlight /usr/local/bin.

Which copies the program to the standard location for user installed programs.

Next, to run it at startup. Still as root, edit /etc/rc.local. Add a line saying /usr/local/bin/backlight N, where N is the number code you want for the brightness.

That should do it.


* Apple Macbook Pro LCD backlight control
* Copyright (C) 2006 Nicolas Boichat <nicolas>
* Copyright (C) 2006 Felipe Alfaro Solana <felipe_alfaro>
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

#include <stdio.h>
#include <sys/io.h>
#include <stdlib.h>

void init()
    if (ioperm(0xB2, 0xB3, 1) < 0)
        perror("ioperm failed (you should be root).");

int get_current_value()
    outb(0x03, 0xB3);
    outb(0xBF, 0xB2);
    char t = inb(0xB3) >> 4;
    return t;

int calculate_new_value(const char *arg)
    int val, new = atoi(arg);

    if (arg[0] == '+' || arg[0] == '-')
        val = new + get_current_value();
        val = new;

    if (val > 15)
        val = 15;
    else if (val < 1)
        val = 1;

    return val;

int main(int argc, char** argv)
    if (argc > 2)
        printf("%s : read current value\n", argv[0]);
        printf("%s value : write value [0-15]\n", argv[0]);


    if (argc < 2)
        printf("Current value : %d\n", get_current_value());

    if (argc == 2)
        int value = calculate_new_value(argv[1]);
        outb(0x04 | (value << 4), 0xB3);
        outb(0xBF, 0xB2);
        printf("new value: %d\n", value);

    return 0;

Getting sound to work in Arch for the Alu' iMac 20" & 24" models:

Add the following to /etc/modprobe.d/sound.conf

options snd-hda-intel model=imac24

The option above may produces tiny sound on imac7,1. To have OSX like rich sound on imac 7,1, add following to /etc/modprobe.d/modprobe.conf

options snd-hda-intel model=mb31

Then restart computer or the sound system.

Using the above gives a workable alsamixer. I've found that using VLC & its mixer is very helpful when watching DVD's. I have not tested the line out or mic, though I believe that they are working properly with this configuration.

A forum thread regarding installation of Arch Linux on the iMac can be found here: