Comment 11 for bug 879710

I just wanted to bump this issue as I've been experiencing it without fail for the last two days and the posted workaround has not resolved the issue. Currently running 11.10 x64. My command line has been:

sudo vmbuilder kvm ubuntu -v --debug --suite=lucid --flavour=virtual --rootsize=4096 --swapsize=1024 --mem=388 --arch=i386 --user=system --pass=changemenow --components=main,universe,restricted --addpkg=acpid --addpkg=openssh-server -o --libvirt qemu:///system

The error noted before crashing out has consistently been:

2012-03-16 13:59:53,564 ERROR : Process (['umount', '/tmp/tmptaOMHF/dev']) returned 1. stdout: , stderr: umount: /tmp/tmptaOMHF/dev: device is busy.
        (In some cases useful info about processes that use
         the device is found by lsof(8) or fuser(1))

Traceback (most recent call last):
  File "/usr/bin/vmbuilder", line 24, in <module>
    cli.main()
  File "/usr/lib/python2.7/dist-packages/VMBuilder/contrib/cli.py", line 216, in main
    distro.build_chroot()
  File "/usr/lib/python2.7/dist-packages/VMBuilder/distro.py", line 84, in build_chroot
    self.call_hooks('configure_os')
  File "/usr/lib/python2.7/dist-packages/VMBuilder/distro.py", line 67, in call_hooks
    call_hooks(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/VMBuilder/util.py", line 165, in call_hooks
    getattr(context, func, log_no_such_method)(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/VMBuilder/plugins/ubuntu/distro.py", line 155, in configure_os
    self.suite.unmount_dev()
  File "/usr/lib/python2.7/dist-packages/VMBuilder/plugins/ubuntu/dapper.py", line 125, in unmount_dev
    run_cmd('umount', '%s/dev' % self.context.chroot_dir)
  File "/usr/lib/python2.7/dist-packages/VMBuilder/util.py", line 120, in run_cmd
    raise VMBuilderException, "Process (%s) returned %d. stdout: %s, stderr: %s" % (args.__repr__(), status, mystdout.buf, mystderr.buf)
VMBuilder.exception.VMBuilderException: Process (['umount', '/tmp/tmptaOMHF/dev']) returned 1. stdout: , stderr: umount: /tmp/tmptaOMHF/dev: device is busy.
        (In some cases useful info about processes that use
         the device is found by lsof(8) or fuser(1))

Prior to the crash, mount indicates indeed, the file (/tmp/tmptaOMHF/dev in this case) is still mounted, the file is also notable in /etc/mtab post-crash.

I've noted that in the lsof results inserted just prior to the mount call, there appear to be three cron processes still accessing /dev/null within the mounted environment (i.e. /tmp/tmptaOMHF/dev/null). I'm attaching a log which contains the results output from the inserted:
"run_cmd('lsof', '%s/dev' % self.context.chroot_dir)" line onward until vmbuilder exits, crashing.

I have successfully built several VMs on this particular machine in the past, using the exact same command, so I was a bit surprised to be running into this issue now, any ideas?