How to change boot device on vm installed on Citrix Xen Server to DVD

I guess your CentOS 6 instance is running in paravirtualized mode and such behavior is just a side effect of it. To access virtual CD/DVD drive, you need to start the instance in recovery mode. From VM menu, select Start/Shut down and Start in recovery mode. This

I had the same issue as B14D3 using the same version of Xenserver and VMs with Centos 6 and 7. I need to resize the file system using gparted, to accomplish that I need to boot from the live dvd.

I can't find the "Start in recovery mode" as referenced on the answer above. I guess it only works with Ubuntu or another OS.

I've found the solution for this problem: xenlens.com Boot a guest VM from CD or DVD in XenServer

Which is basically executing this command in any of the hosts of the pool:

xe vm-param-set HVM-boot-policy="BIOS order" uuid=[uuid of your vm]

You can find the uuid of your vm in the "VM general properties" of each VM. Find the row where it says "UUID"

After running the command you will see the boot options (I tried to include an screen shot but I don't have enough reputation)

I hope it helps.

Philippe.