If you are managing number of virtual machine in XEN kernel and want to reset the root password to any virtual machine can change the password in single user mode.

We have already discussed about root password changes in local machine so just following the same steps in XEN Server.

Before that refer the XEN Commands,

Step 1 : Start your virtual machine, assume that the name of virtual machine  is testing 

#  xm create /xen/testing.cfg

Using config file "/xen/testing.cfg".
Using to parse /boot/grub/grub.conf
Started domain testing

Open console immediately by the below command  and press down or up arrow keys
# xm console testing

 Press  "ENTER" on  vmlinuz-2.6.32-71.29.1.el6.x86_64

step 2:  Choose your booting kernel " kernel /boot/vmlinuz-2.6.32-71.29.1.el6.x86_64 console=hvc0 xencons=t>"  then  Press "e" to  change kernel arguments

step3 : Virtual machine run in single user user so type a word "single" or "1" or "S" and press enter button,

step 4: Can view previous status and press "b" key  your virtual machine will booing in single user mode

Step 5 : Execute the command passwd and enter the root password twise
[root@testing /]# passwd

Changing password for user root.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.

Finally execute init 6 for reboot it.
[root@testing /]# init 6