Unable to install 64-bit VM using KVM

Question

I'm trying to install a 64-bit VM on a 64-bit host Ubuntu 11.04 server. I am using the 64-bit iso (ubuntu-11.10-desktop-amd64.iso) and I set the architecture to x86_64 but when I install the VM it installs the 32 bit kernel. The CPU in the VM reports supporting 64-bit but the kernel but uname -m reports i686.

Answer 1

Okay, My answer consist of two sections:

1. Short Answer : You can't run a 64bit VM on a 32-bit processor. However, you can run a 64bit VM if you have a 64bit processor but have installed a 32bit host OS and your processor supports the right extensions.

2. Long Answer :

Make sure your processor supports virtualization extensions. Both AMD and Intel have processors that support this technology. You can check it from the /proc/cpuinfo file. Look at the flags section for one of two values, vmx or svm.

vmx - (Intel)

svm - (AMD)

Issue this command, egrep '(vmx|svm)' /proc/cpuinfo. If your system supports VT, then you will see vmx or svm in the list of flags. An example output would be,

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr lahf_lm

NOTE : These flags say that your processor supports VT technology. However, VT technology can still be disabled in your computer’s BIOS. So make sure it has enabled from BIOS.

Optionally, you can use one of these tools, Processor Check for 64-Bit Compatibility from VMWare or Intel® Processor Identification Utility

According to this document from VMWare,

64-bit guest operating system support: 64-bit guest operating systems will run on 64-bit hardware independent of the type of host operating system. 64-bit guest operating systems offer direct access to more memory than 32-bit systems ...

Therefore, if your processor supports 64bit architecture and has VT extensions, you can run 64bit VMs.

Assume this info will help you :)