How you can determine a linux server is a virtual machine or not

So you logged in a linux box remotely and you don't know if it is a virtual machine or a physical machine. Additionally it can be created by using any of the virtualization vendor's platform such as Citrix XenServer, RHEV, VMware etc.

One and reliable way of determining whether the OS is vm or physical is looking lscpu command's output. lscpu command displays information about the CPU architecture. When a virtual machine is created, hypervisor vendor info should be appeared in the output.

Some examples are:

A Physical Server

# lscpu

Architecture: x86_64

CPU op-mode(s): 32-bit, 64-bit

Byte Order: Little Endian

CPU(s): 16

Thread(s) per core: 2

Core(s) per socket: 4

CPU socket(s): 2

Vendor ID: GenuineIntel

CPU family: 6

Model: 47

Stepping: 2

CPU MHz: 2394.023

BogoMIPS: 4787.84

Virtualization: VT-x

A KVM virtualization

# lscpu

Architecture: x86_64

CPU op-mode(s): 32-bit, 64-bit

Byte Order: Little Endian

CPU(s): 6

On-line CPU(s) list: 0-5

Thread(s) per core: 1

Core(s) per socket: 1

CPU socket(s): 6

Vendor ID: GenuineIntel

CPU family: 6

Model: 13

Stepping: 3

CPU MHz: 3065.518

BogoMIPS: 6131.03

Hypervisor vendor: KVM

Virtualization type: full

An Oracle VM

# lscpu

Architecture: x86_64

CPU op-mode(s): 32-bit, 64-bit

Byte Order: Little Endian

CPU(s): 4

On-line CPU(s) list: 0-3

Thread(s) per core: 4

Core(s) per socket: 1

Socket(s): 1

Vendor ID: GenuineIntel

CPU family: 6

Model: 44

Stepping: 2

CPU MHz: 2400.130

BogoMIPS: 4800.26

Hypervisor vendor: Xen

Virtualization type: para