[root@localhost work]# yum -c ./yum-xen.conf --installroot=./mountloc --noplugins -y groupinstall Base
error: cannot open Packages index using db3 - No such file or directory (2)
error: cannot open Packages database in ./mountloc/var/lib/rpm
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in ?
    yummain.main(sys.argv[1:])
  File "/usr/share/yum-cli/yummain.py", line 82, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 205, in getOptionsConfig
    errorlevel=opts.errorlevel)
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 125, in doConfigSetup
    self.conf = config.readMainConfig(startupconf)
  File "/usr/lib/python2.4/site-packages/yum/config.py", line 598, in readMainConfig
    yumvars['releasever'] = _getsysver(startupconf.installroot, startupconf.distroverpkg)
  File "/usr/lib/python2.4/site-packages/yum/config.py", line 661, in _getsysver
    idx = ts.dbMatch('provides', distroverpkg)
TypeError: rpmdb open failed