LightDM hangs after a few seconds on my Power Mac G4 (FW800, ATI Radeon 9000 Graphics)

[Jonathan Alfonso]

Hi, I use Ubuntu 12.04 on my Power Mac G4, and it's been running great minus the lack of composition support. When upgrading to Ubuntu 14.04 and then applying the needed boot flags to Yaboot, LightDM launched but hung after a few seconds. When it did not hang, it refused to load any sessions (Unity, Gnome Session Flashback). I have since reinstalled Ubuntu 12.04, but I am willing to reinstall Ubuntu 14.04 for the sake of testing. Thanks.

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lspci output
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0000:00:0b.0 Host bridge: Apple Inc. UniNorth 2 AGP
0000:00:10.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV250 [Radeon 9000 Series]
0001:10:0b.0 Host bridge: Apple Inc. UniNorth 2 PCI
0001:10:15.0 USB controller: NEC Corporation OHCI USB Controller (rev 41)
0001:10:15.1 USB controller: NEC Corporation OHCI USB Controller (rev 41)
0001:10:15.2 USB controller: NEC Corporation uPD72010x USB 2.0 Controller (rev 02)
0001:10:16.0 Network controller: Broadcom Corporation BCM4306 802.11b/g Wireless LAN Controller (rev 03)
0001:10:17.0 Unassigned class [ff00]: Apple Inc. KeyLargo Mac I/O (rev 03)
0001:10:18.0 USB controller: Apple Inc. KeyLargo USB
0001:10:19.0 USB controller: Apple Inc. KeyLargo USB
0001:10:1b.0 USB controller: NEC Corporation OHCI USB Controller (rev 43)
0001:10:1b.1 USB controller: NEC Corporation OHCI USB Controller (rev 43)
0001:10:1b.2 USB controller: NEC Corporation uPD72010x USB 2.0 Controller (rev 04)
0002:20:0b.0 Host bridge: Apple Inc. UniNorth 2 Internal PCI
0002:20:0d.0 Unassigned class [ff00]: Apple Inc. UniNorth 2 ATA/100
0002:20:0e.0 FireWire (IEEE 1394): Apple Inc. UniNorth 2 FireWire (rev 01)
0002:20:0f.0 Ethernet controller: Apple Inc. UniNorth 2 GMAC (Sun GEM)