The following guide can be used to reset an administrative root password on XenServer 7 Linux.
Enter XenServer Boot Menu
In the first step, reboot your XenServer into Grub boot menu:
Edit XenServer boot menu entry
Use arrows to locate an appropriate XenServer boot menu entry and press e. Doing so you will edditing mode.
While in the editing mode locate read-only parameter ro and replace it with rw. Furthermore, locate keyword splash and replace it with init=/bin/bash. The resulting edited menu item should look similar to the one illustrated below:
Boot into single mode
Once you changed the boot meny entry, hit F10 thus you will boot into a single mode:
Reset your root password
Once you enter into a single mode use passwd command to reset your XenServer's root password:
At this stage our XenServer root password should be updated. Reboot your system be entering the command exec /usr/sbin/init
New root password
If everyting went well you should now be able to login with your new XenServer password: