Checking If Server Is Physical Or Virtual

There are several ways to check if the server is a physical server or virtual server. Post list just two such methods.

1. Using dmidecode
Among many information listed by the dmidecode command (requires root access) one is the system-manufacturer string. If this is a physical server the command will output the vendor name, if not it will output the virtual software name.
On physical servers

# dmidecode -s system-manufacturer
Dell Inc.

# dmidecode -s system-manufacturer
IBM

On Virtual servers

# dmidecode -s system-manufacturer
VMware, Inc.

# dmidecode -s system-manufacturer
innotek GmbH

The innotek GmbH is from a VM server created with VirtualBox
There are other strings in the demidecode output that could also be used to find out which the server is physical or virtual.
Grep on Product on physical servers returns

# dmidecode | grep Product
        Product Name: PowerEdge M610
        Product Name: 02Y41P
        Product Name:

# dmidecode | grep Product
        Product Name: IBM System x3550 M4 Server -[7914ZT7]-
        Product Name: 00J6242

On virtual servers return

# dmidecode | grep Product
        Product Name: VMware Virtual Platform
        Product Name: 440BX Desktop Reference Platform

# dmidecode | grep Product
        Product Name: VirtualBox
        Product Name: VirtualBox

It's also possible to grep on the string Virtual. Output from physical servers.

# dmidecode | grep Virtual
                VME (Virtual mode extension)

# dmidecode | grep Virtual
                VME (Virtual mode extension)
                Enhanced Virtualization

Output from virtual servers

# dmidecode | grep Virtual
        Product Name: VMware Virtual Platform
                VME (Virtual mode extension)
                VME (Virtual mode extension)
                VME (Virtual mode extension)
                VME (Virtual mode extension)
        String 2: Welcome to the Virtual Machine

# dmidecode | grep Virtual
        Version: VirtualBox
        Product Name: VirtualBox
        Family: Virtual Machine
        Product Name: VirtualBox

2. Using virt-what
virt-what (included in virt-what-*.rpm, comes with RedHat and other distros) checks if the running system is a physical or virtual. This command must be run as root user.
On physical servers the command does not return anything and goes back to prompt.

[root@srv6 ~]# virt-what
[root@srv6 ~]#

On virtual servers

# virt-what
vmware

# virt-what
virtualbox