There are some PowerMacs that still have good support on Ubuntu and debian. And there are some models that don't work well or barely. An eMac G4 1.25 GHz hasn't worked with Ubuntu 9.04. And the iMac G4 800MHz neither with Ubuntu 10.10 nor with debian 6 (squeeze) rc1. A solution.

This is a very sad situation. Apple doesn't support those Macs with SnowLeopard or Leopard at all. There is only Linux for an descent OS. And it has some hurdles.

Xorg likes to get user-friendly. There shouldn't be a xorg.conf any more. Xorg will make it. Fine thing. Until you give Xorg those special old Apple-crippled graphic hardware. It fails.

But Xorg and the Apple hardware have worked and still work pretty well. All we have to do is to configure it. Let's do it. I will share a xorg.conf that will work with Ubuntu 10.10 and an eMac G4 1.25GHz. And one for an iMac G4 TFT 800MHz that works with debian 6. A drawback: Ubuntu installs well on the iMac G4 but after the first restart the TFT is black and won't change. It's unusable. You can't switch to a console. And one step beyond, Ubuntu doesn't have a sshd installed by default. To make it worked, you have to boot a rescue system, mount the disk and copy the xorg.conf on it.

xorg.conf for eMac G4 1.25GHz

Section "Device"
        Identifier      "Radeon9200"
        BusID           "PCI:0:16:0"
        Driver          "fbdev"
        Option          "UseFBDev"              "true"
EndSection

        # EDID version 1 revision 3
Section "Monitor"
        # Block type: 2:0 3:fd
        # Block type: 2:0 3:fc
        Identifier "iMac"
        VendorName "APP"
        ModelName "iMac"
        # Block type: 2:0 3:fd
        HorizSync 71-73
        VertRefresh 70-140
        # Max dot clock (video bandwidth) 130 MHz
        # Block type: 2:0 3:fc
        # DPMS capabilities: Active off:no  Suspend:no  Standby:no
        Option  "DPMS"

        Mode    "1024x768"      # vfreq 88.995Hz, hfreq 72.086kHz
                DotClock        99.190000
                HTimings        1024 1072 1168 1376
                VTimings        768 769 772 810
                Flags   "+HSync" "+VSync"
        EndMode
        Mode    "1280x960"      # vfreq 71.932Hz, hfreq 72.075kHz
                DotClock        122.240000
                HTimings        1280 1328 1424 1696
                VTimings        960 961 964 1002
                Flags   "+HSync" "+VSync"
        EndMode
        # Block type: 2:0 3:fd
        # Block type: 2:0 3:fc
EndSection

Section "Screen"
        Identifier "Default Screen"
        Device "Radeon9200"
        Monitor "iMac"
        DefaultDepth 24
        SubSection "Display"
                Depth 8
                Modes "1280x960" "1024x768"
        EndSubSection
        SubSection "Display"
                Depth 15
                Modes "1280x960" "1024x768"
        EndSubSection
        SubSection "Display"
                Depth 16
                Modes "1280x960" "1024x768"
        EndSubSection
        SubSection "Display"
                Depth 24
                Modes "1280x960" "1024x768"
        EndSubSection
EndSection

Section "ServerLayout"
        Identifier "Default Layout"
        Screen "Default Screen"
EndSection

xorg.conf for iMac G4 800 MHz

Section "Device"
	Identifier	"Gforce2MX"
	BusID		"PCI:0:16:0"
	Driver		"fbdev"
	Option		"UseFBDev"	"true"
EndSection

	# EDID version 1 revision 3
Section "Monitor"
	# Block type: 2:0 3:fe
	# Block type: 2:0 3:fe
	# Block type: 2:0 3:fc
	Identifier "iMacLamp"
	VendorName "APP"
	ModelName "Color LCD"
	# Block type: 2:0 3:fe
	# Block type: 2:0 3:fe
	# Block type: 2:0 3:fc
	# DPMS capabilities: Active off:yes  Suspend:no  Standby:no

	Mode 	"1024x768"	# vfreq 60.004Hz, hfreq 48.363kHz
		DotClock	65.000000
		HTimings	1024 1048 1184 1344
		VTimings	768 771 777 806
		Flags	"-HSync" "-VSync"
	EndMode
	# Block type: 2:0 3:fe
	# Block type: 2:0 3:fe
	# Block type: 2:0 3:fc
EndSection

Section "Screen"
	Identifier	"Default Screen"
	Device		"Gforce2MX"
	Monitor		"iMacLamp"
	DefaultDepth	24
	SubSection "Display"
		Depth 24
		Modes "1024x768"
	EndSubSection
EndSection

Section "ServerLayout"
	Identifier "Default Layout"
	Screen "Default Screen"
EndSection

If you need a "Monitor" Section for your special setup, you should rely on read-edid by John Fremlin on polypux.org. On a apt-system install the package read-edid. And a hint, read-edid isn't the command, use get-edid | parse-edid to get a good "Section".

And as you can see, I use the graphic device driver fbdev and not the "vendor" driver, like "ati" or "nv". The only reason: It works. There are some academic drawbacks. But don't expect to get a full blown 3D accelerated device by getting "nv" or "ati" to work.