Am I running on a VM?

This is a regular question - have I logged in to a physical linux server or is this a virtual machine?

One simple way of finding this out (if you have root access) is to check the Chassis in dmidecode. Here are a few examples:

myuser@myopennebulahost:~$ sudo dmidecode -s chassis-manufacturer
Dell Inc.
myuser@myopennebulahost:~$

myuser@buildserver:~$ sudo dmidecode -s chassis-manufacturer
HP
myuser@buildserver:~$

myuser@apacheserver:~$ sudo dmidecode -s chassis-manufacturer

QEMU

myuser@apacheserver:~$

We can see that the OpenNebula server is a Dell, and the build server is an HP. But the Apache server is QEMU, which is a common virtualization hardware emulator. Clearly the Apache server is a VM.

Edit:
I've noticed that some Red hat VMs return Red Hat, not QEMU
[root@freepbx ~]# dmidecode -s chassis-manufacturer
Red Hat

[root@freepbx ~]#