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