Answer:

To list all active guest domains in Xen, you can use the xm list command.

# xm list

Name                                ID  Mem(MiB)   VCPUs      State      Time(s)
Domain-0                            0     768       2         r-----     1029.3
Web-server                         12     256       1         -b----       13.7

Answer:

In order to convert a VM image (file based) running in Xen and to use in the Virtual Box, you can use the following tricks.

# VBoxManage convertfromraw -format VDI filename.img filename.vdi

That is it.

Answer:

In Xen, the clocks of all VMs are controlled by dom0, in order to make ntp work independently, you can edit the file "/etc/sysctl.conf"

xen.independent_wallclock = 1

Restart your server to take effects.