Tuesday, 31 May 2011

VMware on Linux: Promiscuous Mode

When VMware Workstation is hosted under Linux, by default it doesn't allow VM Guests to access the network in Promiscuous mode.  There's an easy fix for this...

If you run something like Wireshark from a VM Guest, you'll see VMware display an error message.

The problem lies with the permissions on the Host.  When VMware is started without root privileges, it doesn't have the permissions necessary to access the /dev/vmnet0 device.

A quick temporary bodge is to use chgrp and chmod on the Host, to tweak the permissions on /dev/vmnet* until the next reboot (where YourGroup is a group that your user account is in - typically adm on my Ubuntu machines):
   chgrp YourGroup /dev/vmnet*
   chmod g+rw /dev/vmnet*

A more permanent fix is to edit /etc/init.d/vmware on the Host, and tweak the ownership and permissions when the device is created, by adding the lines in red:
  # Start the virtual ethernet kernel service
   vmwareStartVmnet() {
      vmwareLoadModule $vnet
      "$BINDIR"/vmware-networks --start >> $VNETLIB_LOG 2>&1
      chgrp adm  /dev/vmnet*
      chmod g+rw /dev/vmnet*

After you restart the Host's VMware daemon ...

   /etc/init.d/vmware stop
   /etc/init.d/vmware start

you'll be able to boot your Guest VM, and use Wireshark or whatever in the Guest.  Just Remember!   Your VM Guest's Network Adapter must be set to BRIDGED (connected directly to the physical network), not NAT (used to share the host's IP address).

Aside: I did think it ought be possible to achieve the same effect a little more cleanly, by creating a file in /etc/udev/rules.d to set the desired ownership and permission modes for /dev/vmnet*.  But nothing I've tried has worked.  Anyone?


  1. Hi Martin,

    I've tried to write an UDEV rule to control the ownership and mode of the created devices, and even saw that UDEV recognized my rule, but the files still got owned by root:root and mode 0600.

    Seems that "vmware-networks" force these permissions on the device files.

  2. Hi Martin,

    I bought a pair of power line adapters and wanted to configure them. The software utility to configure the adapters only works on Windows and I only had a Windows 7 instance in a VM running on Ubuntu. The software installed winpcap which required setting the card in promiscuous mode. After struggling for several hours, I came across your blog. I followed your instructions exactly and after a couple of tries it worked perfectly. Thank you very much the help.


  3. Thanks! I spent two days trying to debug this.

  4. Thanks, It have worked for me even if the guest's network, was on Host mode .

  5. Thanks for your post, you have save me a lot of time :)

  6. Why it should be set to bridget and not nat? Why it won't work for nat "vmnet8" device?

    Thanks for the great post.

  7. Hi Hesham. I wasn't sure that promiscuous mode would actually work in NAT mode, but maybe it would be OK. Generally I try to avoid NAT where it's not strictly necessary, as it can make some protocols less reliable. Also my day job is security testing, where NAT is not appropriate because it could reduce accuracy of scan results.


    - Martin


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