Forwarding this bug from Ubuntu reporter jerrylamos:
With external 1280x1024 screen set on and laptop screen off in System Preferences Monitors, boot hangs showing splash screen with kernel 2.6.35-5-generic. Boots fine with kernel 2.6.34-5-generic.
ATI Technologies Inc Radeon Mobility M7 LW [Radeon Mobility 7500] IBM Thinkpad T40
Attached is Xorg.0.log, xsession-errors, dmesg obtained with ssh from another pc on the network.
Updated to 2.6.35-6, tested again, and X hangs during boot again.
fixes it, I think, booted a couple times O.K.
Tried it by hand on boot editing the linux line, then by altering /etc/default/grub to
quiet splash radeon.modeset=0
worked both times.
Do note on another of my pc's booting Maverick with intel driver I use
Maverick KMS is buggy on two of my three pc's. The one that is booting O.K. has Radeon Xpress 200. I'll check it tonight to see if KMS is in fact on.
2.6.34-5 will boot with KMS on.
Ctrl-Alt-F1 switches to text screen O.K.
Ctrl-Alt-F7 to switch back to desktop fails. Screens freeze. ssh still works.
Attached is dmesg & Xorg.0.log by ssh from another pc on the net.
Created attachment 36793 [details]
Info from ssh
Created attachment 36794 [details]
dmesg from hang
Created attachment 36795 [details]
dmesg & Xorg.0.log
Problem resolved for original report back in 2010.