According to the Citrix documentation, the command to mount the XenServer tools ISO image on a Linux OS is this:

mount /dev/xvdd /mnt

But this does not work on CentOS or Ubuntu virtual machines, because these use a different naming convention for CD-ROM devices.

Mount XenServer Tools in CentOS

sudo mount /dev/cdrom1 /mnt

Mount XenServer Tools in CentOS 7

sudo mount /dev/sr0 /mnt

Mount XenServer Tools in Ubuntu

sudo mount /dev/cdrom /mnt