Update: You may be interested in the perl module implementing these tricks.

Frequently, our customers want to install our software in a virtual machine. This can be OK, but frequently they hit a CPU, memory, or IO limit caused by running in a constrained virtual environment. When this happens, we really like to know if they're running under virtualization when we try to support them. Here's some tricks to detect, from a shell, if the system is virtualized.

The first thing to check is dmesg. On a recently-booted system, checking the 'dmesg' command output may be sufficient. Otherwise, try "cat /var/log/dmesg" instead of "dmesg"

• VMWare:

   # dmesg | grep -i virtual
   VMware vmxnet virtual NIC driver
     Vendor: VMware    Model: Virtual disk      Rev: 1.0 
   hda: VMware Virtual IDE CDROM Drive, ATAPI CD/DVD-ROM drive
  

• QEmu or KVM:

  If the "-cpu host" option has not been used, QEmu and KVM will identify themselves as:

   # dmesg | grep -i virtual
   CPU: AMD QEMU Virtual CPU version 0.9.1 stepping 03
  

  otherwise, the host's CPU information will be used both in dmesg, or in /proc/cpuinfo.

  However, you should see something like:

   $ dmesg | grep -i virtual
   [    0.000000] Booting paravirtualized kernel on KVM
  

  on newer kernels that understand that they're running under paravirtualization. (Thanks to René Pfeiffer for pointing this out)

• Microsoft VirtualPC:

   # dmesg | grep -i virtual
   hda: Virtual HD, ATA DISK drive
   hdc: Virtual CD, ATAPI CD/DVD-ROM drive
  

• Xen (thanks, wardi and others)

  # dmesg | grep -i xen
  Xen virtual console successfully installed as tty1
  

• Virtuozzo

  # dmesg
  (returns no output)
  
  # cat /var/log/dmesg
  (returns no output)
  
  # ls -al /proc/vz
  veinfo  veinfo_redir  veredir  vestat  vzaquota  vzdata
  

On longer-running systems, you may need to grep /var/log/dmesg instead.

If that doesn't produce anything useful, try using dmidecode to look at the BIOS information. Frequently, there will be at least one component identifying itself as virtualized:

• VMWare:

   # dmidecode | egrep -i 'manufacturer|product'
   Manufacturer: VMware, Inc.
   Product Name: VMware Virtual Platform
  

• Microsoft VirtualPC:

   # dmidecode | egrep -i 'manufacturer|product'
   Manufacturer: Microsoft Corporation
   Product Name: Virtual Machine
  

• QEMU or KVM:

   # dmidecode | egrep -i 'vendor'
   Vendor: QEMU
  

• Virtuozzo:

   # dmidecode
   /dev/mem: Permission denied
  

• Xen:

   # dmidecode | grep -i domU
         Product Name: HVM domU
  

You should just examine the output of dmidecode directly rather than trying to grep as above, in case the output changes. QEMU, for example, doesn't report the vendor in all versions.

Next, check disk devices for identification as virtualized:

• VMWare:

  # cat /proc/ide/hd*/model
  VMware Virtual IDE CDROM Drive
  # cat /proc/scsi/scsi
  Attached devices:
  Host: scsi0 Channel: 00 Id: 00 Lun: 00
    Vendor: VMware   Model: Virtual disk     Rev: 1.0 
    Type:   Direct-Access                    ANSI SCSI revision: 02
  

• Microsoft VirtualPC:

  # cat /proc/ide/hd*/model
  Virtual HD
  Virtual CD
  

• QEMU, KVM, or Xen:

  # cat /proc/ide/hd*/model
  QEMU HARDDISK
  QEMU DVD-ROM
  

• Virtuozzo:

  # ls -al /dev/vzfs
  b-----x--- 1 root root 0, 19 2009-04-06 15:04 /dev/vzfs
  

If you've got tips for other virtualized environments, let me know and I'll add them to the list.