In case if you unable to login through ssh connection or you want to reset root password, can do update in single user mode on Xen virtualization,

Once logged into your XEN main server, execute below command,

Syntax :

xm create -c domain-name.cfg
 

# xm create -c  /xen/domain-name.cfg

Will be shows output like below image,

/

Then press "e" , next choose kernel,



Again press "e" button,then type boot line requirements  "single" or "S"  press enter key,