10.5: Bypass the installer's system requirements check

Nov 01, '07 07:30:00AM

Contributed by: vorlonwarrior

Apple usually weeds out a few machines with new versions of OS X, but 10.5 is the first release I'm aware of that will exclude a larger number of machines from being able to run the new OS. For example, my trusty G4 fails to meet the minimum processor requirements -- it has enough RAM to run 10.5, but the installer prevents me from installing. I doubt I'll be alone here.

All is not lost, however, as it is possible to modify the file that checks the machine specs and decides if 10.5 can be installed.

We first need to restore the 10.5 DVD onto a read/write media. I typically use an external FireWire drive for this. It is as simple as attaching the drive and inserting the DVD into the machine. Then launch Disk Utility and select the drive/partition to restore the DVD onto. Drag the DVD to the source area and the drive/partition to the destination area, and start the restore.

If this was 10.4, we could simply edit the Distribution file in the mpkg file, but Apple has changed things -- they now use xar to compress the mpkg file, so we'll need to decompress the mpkg file and then edit the Distribution file.

Here is what needs to be done:

  1. Download xar (tar and gz file).
  2. Expand the tar.gz file and open terminal and cd into its directory.
  3. Issue the folowing commands, pressing Return between each one and then waiting for its completion (Developer Tools required):
    $ ./configure
    $ make
    $ sudo make install
  4. Check that the install is in the right location (/usr » local » bin » xar) by issuing which xar; it should return the aforementioned location.
  5. Copy the required mpkg to the desktop. For 10.5, the package we want is in /System » Installation » Packages/ folder on the drive with 10.5, and is called OSInstall.mpkg.
  6. Create a new folder on the desktop, eg; OSInstall. Go into Terminal and cd into this folder, then issue the following command to decompress the mpkg to the folder:
    $ xar -x -f /path/to/OSInstall.mpkg
  7. Go into the OSInstall folder, and you'll see a Distribution file and Packages folder.
  8. Open the Distribution file in a text editor, for example I use BBEdit. It's an xml script, so you can just edit it. Look for minRam and the processor speed requirments, and change these, and any other options which could prevent install on your setup. Save the changes.
  9. Issue the following command to compress the files back into xar'd mpkg file: xar -c -f OSInstall.mpkg *.
  10. The OSInstall folder should now have a new OSInstall.mpkg file in it. We then need to copy this new file into /System » Installation » Packages folder on the drive with 10.5. Firstly I'd rename the existing OSInstall.mpkg so we have a copy of it, so cd into the /System » Installation » Packages folder on the drive with 10.5, and issue the following command in Terminal:
    $ sudo mv OSInstall.mpkg OSInstall_orig.mpkg
  11. We then need to copy over the new package, so issue the following command in Terminal:

    sudo copy /path/to/OSInstall.mpkg /Volumes/name_of_105_disk/System/Installation/Packages/OSInstall.mpkg
Now that all remains is to go into the Startup Disk preference pane and select the drive we copied 10.5 to, boot from that drive, and you should then be able to install without issues.

One major thing worthy of note. Do not try and run the installer on a machine with 256MB or less of RAM, in fact, you probably want at least 384MB RAM. I did try 256MB and found the installer simply would not complete, and this was on a machine whose processor was within the the range specified by Apple.

[robg adds: I have heard from a friend who used this technique to install Leopard on a G4 Cube, and he said that it runs "just fine," though I'm not sure of the details behind that statement.]

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