Comment 13 for bug 946022

I have this problem too - it's happening on roughly half my slice builds.

It seems to be due to the grub installation failing, here's what it shows for a build that won't boot:

 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,044 DEBUG : ['chroot', '/tmp/tmpgvQfyy', 'grub', '--device-map=/tmp/vmbuilder-grub/device.map', '--batch']
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,044 DEBUG : stdin was set and it was a string: root (hd0,0)
 ** [out :: host-nwtn1.nwtn] setup (hd0)
 ** [out :: host-nwtn1.nwtn] EOT
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,197 DEBUG :
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,197 DEBUG : [ Minimal BASH-like line editing is supported. For
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,198 DEBUG : the first word, TAB lists possible command
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,198 DEBUG : completions. Anywhere else TAB lists the possible
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,198 DEBUG : completions of a device/filename. ]
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,198 DEBUG : grub> root (hd0,0)
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,198 DEBUG : grub> setup (hd0)
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,198 DEBUG : Checking if "/boot/grub/stage1" exists... no
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,199 DEBUG : Checking if "/grub/stage1" exists... no
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,199 DEBUG :
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,199 DEBUG : Error 15: File not found
 ** [out :: host-nwtn1.nwtn] 2013-03-17 10:52:33,199 DEBUG : grub> EOT

And here's what it shows for a build that does boot:

 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,423 DEBUG : ['chroot', '/tmp/tmpnUU59C', 'grub', '--device-map=/tmp/vmbuilder-grub/device.map', '--batch']
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,424 DEBUG : stdin was set and it was a string: root (hd0,0)
 ** [out :: host-nwtn1.nwtn] setup (hd0)
 ** [out :: host-nwtn1.nwtn] EOT
 ** [out :: host-nwtn1.nwtn]
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,599 DEBUG :
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,599 DEBUG : [ Minimal BASH-like line editing is supported. For
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,599 DEBUG : the first word, TAB lists possible command
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,599 DEBUG : completions. Anywhere else TAB lists the possible
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,599 DEBUG : completions of a device/filename. ]
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,599 DEBUG : grub> root (hd0,0)
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : grub> setup (hd0)
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : Checking if "/boot/grub/stage1" exists... yes
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : Checking if "/boot/grub/stage2" exists... yes
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : Running "embed /boot/grub/e2fs_stage1_5 (hd0)"... 21 sectors are embedded.
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : succeeded
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : Running "install /boot/grub/stage1 (hd0) (hd0)1+21 p (hd0,0)/boot/grub/stage2 /boot/grub/menu.lst"... succeeded
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : Done.
 ** [out :: host-nwtn1.nwtn] 2013-03-17 11:00:01,600 DEBUG : grub> EOT

There are some other errors elsewhere in the process that may or may not be significant. I've attached the full log for both the failed and successful builds.