[总结] YUM错误： error: cannot open Packages database in /%{_dbpath}

给一个客户安装lnmp时遇到这个问题：
Loaded plugins: fastestmirror
error: no dbpath has been set
error: cannot open Packages database in /%{_dbpath}
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in ?
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 309, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 157, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 187, in getOptionsConfig
    self.conf
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 664, in <lambda>
    conf = property(fget=lambda self: self._getConfig(),
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 239, in _getConfig
    self._conf = config.readMainConfig(startupconf)
  File "/usr/lib/python2.4/site-packages/yum/config.py", line 804, in readMainConfig
    yumvars['releasever'] = _getsysver(startupconf.installroot, startupconf.distroverpkg)
  File "/usr/lib/python2.4/site-packages/yum/config.py", line 877, in _getsysver
    idx = ts.dbMatch('provides', distroverpkg)
TypeError: rpmdb open failed

首先找了一下网上的解决方法是：
执行：yum clean all
rm -f /var/lib/rpm/__db*
rpm --rebuilddb
yum update
不过，我用的方法更简单reboot 重启了一下问题就解决了。。。好像是rpmdb的问题。