Ubuntu不能正常登录在ubuntu登录界面，输入密码后，出现一个界面后一闪而过又返回登录界面。查看auth.log发现如下错误
May 15 15:42:19 tim-vm lightdm: pam_unix(lightdm-greeter:session): session opened for user lightdm by (uid=0)May 15 15:42:20 tim-vm lightdm: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directoryMay 15 15:42:20 tim-vm lightdm: PAM adding faulty module: pam_kwallet.soMay 15 15:42:20 tim-vm lightdm: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "tim"May 15 15:42:24 tim-vm lightdm: pam_unix(lightdm-greeter:session): session closed for user lightdm
google之后，在askubuntu发现了同样的错误http://askubuntu.com/questions/161736/ubuntu-box-just-redisplaying-login-screen-after-update。
是因为.Xauthority文件权限的问题，这个权限都变成了root.
将其更改为用户名即可